chapter ii-a: solubility modulation of bicalutamide using...

Chapter II-a: Solubility Modulation of Bicalutamide Using Porous Silica Introduction

Release Modification Designs for Poorly Water Soluble Drugs - 80 -

Approximately 40% of the new drugs fall into category of poorly water soluble drugs (Dong-qin

et al., 2007). The poor solubility in turn affects bioavailability of the drug. Thus a formulator

always faces a challenge in modulation of solubility for these drugs. Various approaches have

been reported in the literature for solubility enhancement ranging from tailoring the active

pharmaceutical ingredient (salt formation) to change in route of administration which includes

Cosolvency (Kapsi and Ayres 2001), hydro tropes (Maheshwari and Jagwani 2011), inclusion

complexes (Lv and Zhang 2012), particle size reduction (Meer et al., 2011), self emulsifying

system (Mura et al., 2012), solid solutions (Srinarong et al., 2011), liquisolid compacts (Tayel et

al., 2008) and hot melt extrusion (Kalivoda et al., 2012). However, most of the approaches faces

demerit of scale up issues or economic challenge.

In the present study bicalutamide (BCL) was used as drug candidate, which is nonsteroidal anti

androgenic and indicated for the treatment of prostate cancer with or without castration. The

drug was approved by USFDA in the year 1995 for the treatment of prostate cancer. BCL

belongs to biopharmaceutics classification system (BCS) class II having poor water solubility

and high permeability (Meer et al., 2011). Several efforts have been made to address this issue

such as bottom up submicronic particulate preparation (Meer et al., 2011), poly (ethylene oxide)-

bicalutamide solid dispersion (Abu-Diak et al., 2012), nanodispersions (Li et al., 2011) and

bicalutamide–β cyclodextrin inclusion complexation (Patil et al., 2008).

Silica is one of the most widely studied excipient. It exists in amorphous to highly ordered

crystalline states. Silica is generally regarded as safe (GRAS). The amorphous silica has lot of

application in pharmaceutics and drug delivery such as glidant (flow promoter), carrier, thickener

and viscosity modifier, adsorbent and preservative. Various reports are available in literature

implementing its use in solubility enhancement by preparing its solid solution/dispersion with the

drug. The examples include Carvedilol (Kovacˇicˇ et al., 2011) drug delivery using Sylysia 350

and spirinolinolactone (Uchino et al., 2007) formulation using Sylysia 730. In the present study,

AEROPERL® 300 Pharma was used as a carrier and adsorbent to formulate drug delivery

system for BCL. Aeroperl®300 Pharma, is an inert amorphous material consisting of colloidal

silicon dioxide with a significantly high pore volume of 1.6 mL/g and consistent spherical shape.

It also has excellent flow and compressibility properties. Aeroperl®300 Pharma in the solid



dispersion can potentially resolve the formulation issues associated with solid dispersions. Also,

Aeroperl®300 Pharma is less likely to promote the reversion of the amorphous drug to

crystalline state on storage of the solid dispersion due to its non crystalline nature. (Gupta et al.,

2001, 2002a, b). Following is the briefing about Aeroper®300 Pharma:

Aeroperl®300 Pharma the excipient developed by Evonik insutries, Germany. Chemically

Aeroperl®300 Pharma is same as of silicon dioxide. Since colloidal silicon dioxide is used as a

raw material whose slurry is prepared and further dried through a process of spray drying. This

results into a high density, porous and spherical particles.

Aeroperl®300 Pharma is dust free, high purity colloidal silicon dioxide. Unlike highly disperse

aerosol products, Aeroperl®300 Pharma consists of bead like mesoporous granules with a

particle size on average of 30 – 40 µ. The high specific surface area of 300 m2/g, coupled with

mesopore volume of 1.6 mL/g means that Aeroperl®300 Pharma is a versatile and highly

absorptive carrier that may be used to incorporate liquids into solid pharmaceutical dosage form.

Advantages of Aeroperl ®300 Pharma include:

High tapped density and nearly spherical shape: Aeroperl®300 Pharma is easy to handle,

even when loaded with more than its weight in liquid.

Hydrophilic nature: Aeroperl®300 Pharma is an efficient desiccant. For example

Aeroperl®300 Pharma may be used in cost effective moisture assisted dry granulation

(MADG) processes to assist in absorbing and distributin the small amount of water used.

High absorption capacity and high surface area: Aeroperl®300 Pharma may help to avoid

costly and time consuming API crystallization.

Solid dispersion prepared using hydrophilic and water soluble excipients often face softness and

tackiness issues. These when mixed with other tableting excipient causes improper mixing and

flow problems. To troubleshoot such issues use of large amount of excipients is reported (Kaur

1980; Sjo¨kvist and Nystro¨m 1991; Owutsu-Ababio 1998). The use of such excipient results

into large tablet weights which often remains impractical. In such circumstances silica often

found to be useful to act as multipurpose but yet single excipient for adsorption, dilution, free

flow and lubrication.



Our idea was to combine the advantageous effects of silica (as reported in literature) with the

hydrophilic liquid for the solubility enhancement of BCL.

Chapter II-a: Solubility Modulation of Bicalutamide Using Porous Silica Rational and Objective


The objective of the present work was to explore solubility enhancement potential of Aeroperl®

300 Pharma for bicalutamide (an anticancer agent). Since Aeroperl® 300 Pharma has a high

surface area, high volume, high purity, dust free and spherical structure it poses itself as a

promising carrier candidate to achieve the target. Therefore, in the present study the objectives

were:

To load drug on Aeroperl® 300 Pharma through a process of slow solvent evaporation

To study the effect of loading in the presence of hydrophilic moieties

To characterize the developed system

To conduct stability studies

Chapter II-a: Solubility Modulation of Bicalutamide Using Porous Silica Experimental


A. FORMULATION DEVELOPMENT

Drug loading efficiency

In a glass test tube with stopper 500 mg of Aeroperl®300 Pharma (AP) was suspended in a 5 mL

acetone solution containing 20 mg/mL of BCL. The system is subjected to isothermal shaking at

25 °C and 75 rpm for the period of 72 h. The solid is then centrifuged at 10,0009g rpm, separated

and dried. The drug loaded AP particles were then subjected to assay analysis. 10 mg of dried

BCL loaded AP particles suspended in 10 ml of acetone prior to sonication and then filtered

using 0.45 l filter. The filtrate is diluted suitably and analyzed spectrophotometrically at 273 nm.

Preparation of BCL-AP

50 mg of polyethylene glycol (average molecular weight of 400) was dissolved in 5 mL of

acetone under stirring. 284 mg of AP was added. After complete homogenization 50 mg of BCL

added. The stirring was continued till complete evaporation of acetone. The solid was then dried

overnight at 60 °C. The powder so obtained was free flowing solid and termed as BCL-AP.

B. CHARACTERIZATION

Fourier transform infra red (FTIR) analysis

The samples were analyzed for their functional groups using IR spectrophotometric analysis

performed using attenuated total reflectance Fourier transform IR (ATR-FTIR)

spectrophotometer (Spectrum 100, Perkin Elmer, USA). A total of 32 scans were performed with

a resolution of 4 cm-1

in triplicates. The samples were mixed with KBr in 1:100 ratio using

mortar and pestle.

Differential scanning colorimetry (DSC) analysis

Thermal behavior was accessed using differential scanning calorimeter (Pyris 6 DSC, Perkin

Elmer, USA). Approximately 5 mg of sample was placed in aluminum pan and crimped using a

press. An empty aluminum pan was used as a blank. DSC studies were performed in the range of

40–250 °C and the heating rate was set to 10 °C/ min.



Powder X-ray diffraction (PXRD) analysis

X-ray diffraction studies were done to determine whether the sample is in crystalline,

paracrystalline or amorphous state. These studies were performed on Rigaku (Miniflex, Japan)

powder X-ray diffractometer using Cu Ka radiation. The PXRD is performed in the most

informative range i.e. 2h values ranging from 10° to 70°. The step scan mode was performed

with a step size of 0.02° at a rate of 2° min-1

.

Scanning electron microscopy (SEM)

To learn the particulate morphologies of the sample scanning electron micrographic studies were

performed on Joel (SEM; JSM-6380LA, Jeol Ltd., Japan). The sample was first coated with gold

in a vacuum sputter for 5 min then mounted on copper stubs provided with double sided carbon

tape. Microscopic images were taken by applying electron current under a voltage difference of

15 kV.

Particle size distribution and specific surface area analysis

Particle size distribution and specific surface area was analysed using dynamic light

scatteringmethod. The samples were analysed in triplicate with laser diffractometer (Malvern

mastersizer 2000, Malvern Instruments, UK).

Dissolution kinetics studies

Dissolution studies were performed using USP type II apparatus (Electrolab, India) operated at

50 rpm. 1,000 ml 1 % sodium lauryl sulphate was used as a dissolution media at 37 ± 0.5 °C. 10

ml of aliquot was drawn at 10, 20, 30 and 60 min time intervals and filtered through 0.45 µ

PTFE filters. Sink condition was maintained throughout the study. The samples were diluted

suitably and quantified for the drug content using UV spectrophotometric method at 273 nm.

These studies were performed in triplicate.

Mathematical modeling of release kinetics (Ahuja et. al., 2007)



The in vitro drug release data was fitted into various kinetic models. Such as Higuchi, first order,

zero order, Hixson–Crowell cube root and Korsmeyer–Peppas models employing the following

set of equation:

First order model:

ln(M0/Mt)= K1t ---------------------------------------(2.1)

Zero order kinetic model:

M0 - Mt = k0t ------------------------------------------(2.2)

Higuchi model:

Mt = K(t)1/2

---------------------------------------------(2.3)

Hixson–Crowell cube root model:

(Wo)1/3

- (Wt)1/3

=k1/3t -------------------------------(2.4)

Koresmeyer–Peppas model:

Mt/M∞ = ktn -------------------------------------------(2.5)

where, M0, Mt and M∞ correspond to the initial amount of drug, amount of drug dissolved at a

particular time, t, and at infinite time, respectively. The terms W0 and Wt refer to the weight of

the drug taken initially and weight of drug dissolved at time t, respectively. Various other terms

like k, ko, k1, k1/3 and K refer to the release kinetic constants obtained from the linear curves of

Korsmeyer–Peppas, zero-order, first-order, Hixson–Crowell cube root law and Higuchi model,

respectively.

C. STABILITY STUDIES

To carry out these studies, the formulation was subjected to 25°C/60% relative humidity

(R.H), 30°C/65% R.H and 40°C/75% R.H as per the stability protocol (table 2.1). Samples were

charged in stability chambers (Thermolab, India) with humidity and temperature control. They

were drawn at specified intervals for analysis over a period of 6 months. Drug content of the

capsules was analyzed using previously developed and validated stability indicating HPLC

method.



Table 2.1. Stability Protocol for BCL-AP

PRODUCT NAME: BICALUTAMIDE CAPSULES 50mg

BATCH NO. BCL-AP T1

APPEARANCE Hard gelatin capsules

TOTAL NO SAMPLE (INCLUDING INITIAL) 400 Capsules

QUANTITY FOR PHYSICAL/ CHEMICAL ANALYSIS 90 capsules

DATE OF STABILITY STARTED 03/2012

REGION FOR TESTING - 6 months (stability testing as per ICH guidelines)

Chapter II-a: Solubility Modulation of Bicalutamide Using Porous Silica Results and Discussion


A. FORMULATION DEVELOPMENT

Drug loading efficiency

The effective uptake of BCL by AP can be significantly monitored by UV spectrophotometric

analysis. The loading efficiency for BCL on AP was found to be 18 % w/w. In order to keep safe

margin from reverse crystallization of BCL, a value of 15 % w/w loading of BCL on AP was

selected for further studies.

B. CHARACTERIZATION

Fourier transform infra red spectroscopy (FTIR)

Figure 2.1 shows FTIR spectra of neat BCL which is characterized by sulphate (1,517 cm-1),

hydroxyl group (3,581 cm-1), carbonyl (1,689 cm-1), amide (3,338 cm-1) and nitrile (2,230 cm-

1). Hydrogen bonding and steric hindrance are often used as a tool to describe the interaction of

drug and carrier (Dinunzio et al. 2008) and carbonyl group remains a powerful hydrogen bond

acceptor (Li et al. 2011) which can form a hydrogen bond with the hydrogen of siloxane present

on silica as evident from the decreased peak intensity of carbonyl group and C–H peak

broadening in BCL-AP system.

(a)

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0

11.2

15

20

25

30

35

40

45

50

55

60

65

69.3

cm-1

%R



(b)

(c)

Fig. 2.1. FTIR spectra of a: AP, b: neat BCL and c: BCL-AP

Differential scanning calorimetry (DSC) studies

Neat BCL (Fig. 2.2) melting can be observed from the sharp endothermic peak at 196 °C. The

physical mixture showing melting of amorphous BCL present within at around 120 °C (Gavin et

al. 2010) and then melting of form II BCL at 195 °C. A slight melting point depression of BCL is

observed in physical mixture when compared with the neat BCL signifying that there is some

interaction between AP and BCL. This trend is also observed by Sanganwar and Gupta (2008)

and Wang et. al. (2006). AP remains almost unaffected to temperature, whereas BCL-AP shows

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0

44.2

50

55

60

65

70

75

80

85

90

95

99.7

cm-1

%R

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0

14.1

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

105

110

115.9

cm-1

%R



a very subtle peak around 200 °C which has masked the melting endothermic peak observed in

neat BCL denoting presence of amorphous phase of BCL in BCL-AP system.

Fig. 2.2. DSC thermogram of a: Physical mixture of AP, PEG and BCL, b: neat BCL, c: neat

AP, d: BCL-AP

Powder X-ray diffraction studies

PXRD of BCL (Fig. 2.3) exhibits presence of peaks at 2h values with very narrow crystal size as

indicated by low peak width. The background bump in the XRD pattern corresponding to

amorphousness of the compound is gradually increasing from neat BCL, physical mixture of

BCL-AP to BCL-AP system. The amorphous systems contains more free energy which often

serves as a driving potential for solubility therefore these systems are more soluble as compared

to that of their crystalline counterpart (Corrigan and Holohan 1984).



Fig. 2.3. XRD of a: neat AP, b: physical mixture of AP and BCL, c: BCL-AP system and d: neat

BCL

Scanning electron microscopy (SEM)

SEM images of neat AP, BCL-AP and neat BCL are shown in Fig. 2.4. Neat AP appear uniform

and spherical carrying porous structures within, while the neat BCL appears needle like with

regularly shaped crystals of several microns in size in aggregated state. By and large in BCLAP

systems the drug was found to be uniformly adsorbed within the pores of AP, acquiring more

surface area as compared to neat BCL thereby achieving rapid dissolution profile.

a b c

Fig. 2.4. Scanning electron micrograph of a: neat AP, b: BCL-AP and c: neat BCL particles

Particle size distribution and specific surface area analysis



Table 2.2 shows the particle size distribution of neat BCL, AP and BCL-AP system. BCL is a

hydrophobic moiety with a large particle size and small surface area. These features caused

dissolution retardation of neat BCL. BCLAP system was also found to have decreased particle

size and surface area. However, the hydrophilicity of BCL-AP system dominated the reduced

surface area and played a pivotal role in achieving improved dissolution.

Table 2.2. Mean particle size and specific surface area of drug, carrier and BCL-AP particles.

Sample Mean particle size

(µm)

Spana Specific surface area (cm

2/g)

Neat bicalutamide 143.26 5.440 0.802 AEROPERL® 300 Pharma 119.82 1.408 1.52 BCL-AP 113.33 2.02 0.216

a Span = (d90-d10)/d50

Dissolution kinetics studies

Figure 2.5 shows dissolution profile of neat BCL, BCL AP physical mixture and BCL-AP

system.

Fig. 2.5. Dissolution profile of bicalutamide from different systems

BCL AP physical mixture demonstrated improved dissolution profile when compared with neat

crystalline BCL. This may be due to an increase of BCL wettability because of AP

hydrophilicity. Significantly improved release profile from BCL-AP was found as compared to

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Dru

g R

ele

ase

d (

%)

Time (min)

BCL-AP

BCL-AP physical mixture

Neat BCL



neat BCL. Approximately 15 times higher solubility of BCL from BCL-AP is achieved in

comparison to neat BCL. This may be due to amorphous content of BCL, and good wetting

properties of AP with hydrophilic environment induced by PEG. The release of BCL found to be

in an anomalous fashion and supported by the Korsmeyer–Peppas model indicating that the drug

released in a non-Fickian manner. Mathematical modeling of release kinetics Table 2 shows the

regression parameters obtained after fitting various release kinetic models to the in vitro

dissolution data. The goodness of fit for various models investigated for BCL-AP ranked in the

order of zero order ˃ Hixson–Crowell cube root law ˃ Korsmeyer– Peppas ˃ Higuchi ˃ first-

order.

Table 2.3. Mathematical model for bicalutamide release

Sr.

No. Formulation

Mathematical models for drug release kinetics

Zero order Hixson crowell

cube root First order Higuchi Korsmeyer-Peppas

Slope r2 Slope r2 Slope r2 Slope r2 Slope r2

1

Neat BCL

-0.037

0.690

-0.004

0.659

-0.006

0.645

0.444

0.798

0.231

0.865

2

Physical

mixture of

BCL and AP

-0.235

0.897

-0.009

0.870

-0.009

0.855

2.714

0.958

0.287

0.980

3

BCL loaded on

AP (BCL-AP)

-1.207

0.998 -0.026

0.990

-0.021

0.975 13.33

0.976

0.616

0.984

The value of slope (n) in Koresemeyer–Peppas model for the systems such as neat BCL, BCL &

AP physical mixture and BCL-AP was found to be 0.865, 0.980 and 0.984 respectively, clearly

indicating a slight non-Fickian drug release behavior. Drug release for the systems having value

of ‘n’ above 0.45 declared as non-Fickian (Ahuja et al. 2007).

C. STABILITY STUDIES

The dissolution pattern of the formulation was also found to be stable during the stability studies

and shown in fig. 2.6.

The developed formulation was subjected to stability studies which upon storage revealed no

significant change in drug content as follows:



(a)

(b)

(c)

Fig.2.6. Dissolution profile of bicalutamide from BCL-AP T1 capsules stored at a: 25 oC/ 60%

RH, b: 30 oC/ 65% RH, and c: 40

oC/ 75% RH

0

20

40

60

80

100

120

0 10 20 30 40 50 60

Dru

g R

ele

ase

d (

%)

Time (Min)

Intitial

1 Month

2 Months

3 months

6 months

0

20

40

60

80

100

120

0 20 40 60 80

Dru

g R

ele

ase

d (

%)

Time (Min)

Intitial

1 Month

2 Months

3 months

6 months

0

20

40

60

80

100

120

0 20 40 60

Dru

g R

ele

ase

d (

%)

Time (Min)

Intitial

1 Month

2 Months

3 Months

6 Months



Table 2.4. Bicalutamide content in BCL-AP T1 capsules during stability testing

Storage condition Time (months) Bicalutamide Assay (%)

Initial 0 103

25 oC/ 60% RH 1 101

25 oC/ 60% RH 2 100

25 oC/ 60% RH 3 102

25 oC/ 60% RH 6 102

30 oC/ 65% RH 1 101

30 oC/ 65% RH 2 101

30 oC/ 65% RH 3 100

30 oC/ 65% RH 6 99

40 oC/ 75% RH 1 100

40 oC/ 75% RH 2 99

40 oC/ 75% RH 3 101

40 oC/ 75% RH 6 99

Chapter II-a: Solubility Modulation of Bicalutamide Using Porous Silica Conclusion


Conclusion

In the present study, solubility enhancement potential of silica for bicalutamide is successfully

demonstrated. The dissolution rate of bicalutamide is enhanced because of amorphous nature of

bicalutamide and good wetting properties induced by AP in combination with PEG. The

proposed system was characterized using various analytical techniques. This strategy can

successfully be extrapolated to number of other drug candidates in a cost effective way for

preparation of immediate release formulations.

Chapter II-a: Solubility Modulation of Bicalutamide Using Porous Silica References


References

Abu-Diak, O. A.; Jones, D. S.; Andrews, G. P. Understanding the performance of melt-extruded

poly(ethylene oxide)-bicalutamide solid dispersions: characterization of microstructural

properties using thermal, spectroscopic and drug release methods. Journal of Pharmaceutical

Sciences 2012, 101, 200–213.

Ahuja, N.; Katare, O. P.; Singh, B. Studies on dissolution enhancement and mathematical

modeling of drug release of a poorly water-soluble drug using water-soluble carriers. European

Journal of Pharmaceutics and Biopharmaceutics 2007, 65, 26–38.

Corrigan, O. I.; Holohan, E. M. Amorphous spray dried hydro flumethiazide - polyvinyl

pyrrolidone systems: physicochemical properties. Journal of Pharmacy and Pharmacology 1984,

36, 217–221.

Dinunzio, J. C.; Miller, D. A.; Yang, W.; Mcginity, G. W.; Williams, R. O. Amorphous

compositions using concentration enhancing polymers for improved bioavailability of

itraconazole. Molecular Pharmaceutics 2008, 5, 968–980.

Dong-qin, Q.; Gui-xia, X.; Xiang-gen, W. Studies on preparation and absolute bioavailability of

a self-emulsifying system containing puerarin. Chemical and Pharmaceutical Bulletin 2007, 55,

800–803.

Gavin, P. A.; Osama, A. A.; David, S. J. Physicochemical characterization of hot melt extruded

bicalutamide-polyvinylpyrrolidone solid dispersions. Journal of Pharmaceutical Sciences 2010,

99, 1322–1325.

Gupta, M. K.; Goldman, D.; Bogner, R. H.; Tseng, Y. C. Enhanced drug dissolution and bulk

properties of solid dispersions granulated with a surface adsorbent. Pharmaceutical Development

and Technology 2001, 6, 563–572.



Gupta, M. K.; Bogner, R. H.; Goldman, D.; Tseng, Y. C. Mechanism for further enhancement in

drug dissolution from solid-dispersion granules upon storage. Pharmaceutical Development and

Technology 2002a, 7, 103–112.

Gupta, M. K.; Tseng, Y. C.; Goldman, D.; Bogner, R. H. Hydrogen bonding with adsorbent

during storage governs drug dissolution from solid-dispersion granules. Pharmaceutical

Research 2002b, 19, 1663–1672.

Kalivoda, A.; Fischbach, M.; Kleinebudde, P. Application of mixtures of polymeric carriers for

dissolution enhancement of oxeglitazar using hot-melt extrusion. International Journal of

Pharmaceutics 2012, 439, 145–156.

Kapsi, S. G.; Ayres, J. W. Processing factors in development of solid solution formulation of

itraconazole for enhancement of drug dissolution and bioavailability. International Journal of

Pharmaceutics 2001, 229, 193–203.

Kaur, R.; Grant, D. J. W.; Eaves, T. Comparison of poly(ethylene glycol) and poly oxyethylene

stearate as excipients for solid dispersion systems of griseofulvin and tolbutamide II: dissolution

and solubility studies. Journal of Pharmaceutical Sciences 1980, 69, 132–1326.

Kovačič, B.; Vrečer, F.; Planinšek, O. Solid dispersions of carvedilol with porous silica.

Chemical and Pharmaceutical Bulletin 2011, 59, 427–433.

Li, C.; Li, C.; Le, Y.; Chen, J. F. Formation of bicalutamide nanodispersion for dissolution rate

enhancement. International Journal of Pharmaceutics 2011a, 404, 257–263.

Lv, H. X.; Zhang, Z. H.; Hui, J.; Waddad, A. Y.; Zhou, J. P. Preparation, physicochemical

characteristics and bioavailability studies of an atorvastatin hydroxypropyl-beta-cyclodextrin

complex. Pharmazie 2012, 67, 46–53.



Maheshwari, R. K.; Jagwani, Y. Mixed hydrotropy: novel science of solubility enhancement.

Journal of Pharmaceutical Sciences 2011, 73, 179–183.

Meer, T. S.; Sawant, K. P.; Amin, P. D. Liquid antisolvent precipitation process for solubility

modulation of bicalutamide. Acta Pharmaceutica 2011, 61, 435–445.

Mura, P.; Valleri, M.; Cirri, M.; Mennini, N. New solid selfmicroemulsifying systems to enhance

dissolution rate of poorly water soluble drugs. Pharmaceutical Development and Technology

2012, 17, 277–284.

Owutsu-Ababio, G.; Ebube, N. K.; Reams, R.; Habib, M. Comparative dissolution studies for

mefanamic acid- poly(ethylene glycol) solid dispersion systems and tablets. Pharmaceutical

Development and Technology 1998, 3, 405–412.

Patil, A. L.; Pore, Y. V.; Kuchekar, B. S.; Late, S. G. Solid-state characterization and dissolution

properties of bicalutamide-betacyclodextrin inclusion complex. Pharmazie 2008, 63, 282–285.

Sanganwar, G. P.; Gupta, R. B. Dissolution-rate enhancement of fenofibrate by adsorption onto

silica using supercritical carbon dioxide. International Journal of Pharmaceutics 2008, 360,

213–218.

Sjökvist, E.; Nyström, C. Physicochemical aspects of drug release IX. Tableting properties of

solid dispersions using xylitol as carrier material. International Journal of Pharmaceutics 1991,

67, 130–153.

Srinarong, P.; Hämäläinen, S.; Visser, M. R.; Hinrichs, W. L.; Ketolainen, J.; Frijlink, H. W.

Surface-active derivative of inulin (Inutec_ SP1) is a superior carrier for solid dispersions with a

high drug load. Journal of Pharmaceutical Sciences 2011, 100, 2333–2342.



Tayel, S.; Soliman, I.; Louis, D. Improvement of dissolution properties of Carbamazepine

through application of the liquisolid tablet technique. European Journal of Pharmaceutics and

Biopharmaceutics 2008, 69, 342–347.

Uchino, T.; Yasuno, N.; Yanagihara, Y.; Suzuki, H. Solid dispersion of spironolactone with

porous silica prepared by the solvent method. Pharmazie 2007, 62, 599–603.

Wang, L.; Cui, F. D.; Sunada, H. Preparation and evaluation of solid dispersions of nitrendipine

prepared with fine silica particles using melt mixing method. Chemical and Pharmaceutical

Bulletin 2006, 54, 37–43.

Chapter II-b: Mesoporous Silica: a Novel Carrier Introduction


Introduction to mesoporous materials

Development of micro and nanotechnology during the previous decades has influenced the

current research of biomedical applications. Controlled-release nanoparticles, quantum dots,

targeted delivery and cancer nanotechnology are all studied in detail, and the results of their

biomedical applications are very encouraging. However, many of these applications of

nanotechnology are still far away from practical use, although the speed of the progress raises

hopes of achieving completely new biomedical applications even in the near future (Salonen et

al., 2008). Mainly these developments are into areas like imaging and sensor technology, and in

the case of drug delivery applications, improved cancer therapy and more efficient and patient

compliant administration of other active pharmaceutical ingredients (APIs). Pharmaceutical

industry has faced problems associated with the development of new drug molecules as

commercial products. Many potential molecules cannot be delivered in oral form due to their

poor and erratic dissolution and/or pharmacokinetic properties, typically poor solubility and

dissolution in the intestinal lumen, poor permeation properties in the GI tract, as well as high

intestinal or hepatic first pass metabolism.

Mesoporous materials own unique and advantageous properties considering drug delivery

applications. Small size of the pores (2–50 nm) confines the space of a drug and engages the

effects of surface interactions of the drug molecules and the pore wall. Depending on the size

and the surface chemistry of the pores, increased dissolution rate or sustained release of drugs

can be obtained (Horcajada et al., 2004, Vallet-Regi 2006). Since the first paper by Vallet- Regi

in 2001 (ibuprofen loaded into mesoporous silica material MCM-41), numerous articles have

been published on these materials with modified pore size (Salonen et al., 2000) and chemical

modifications of the surfaces (Munoz et al., 2003; Schwartz et al., 2005), in vitro studies,

including calcification (Canham 1995; Canham et al., 1996a), cell adhesion and culturing

(Bayliss et al., 1999; Chin et al., 2001; Low et al., 2006), neural networks (Sapelkin et al., 2006),

protein adsorption (Collins et al., 2002; Karlsson et al., 2003), and biodegradability studies

(Canham et al., 1999; Anderson et al., 2003). Also some in vivo assessments of tissue

compatibility have been carried out (Bowditch et al., 1999, Rosengren et al., 2000). While the

highly porous silica with porosity of more than 70% dissolves readily in simulated body fluids

(except in the simulated gastric fluid), silica with porosity of < 70% is bioactive and slowly

biodegradable. The very low porosity Si and macroporous Si are quite bioinert materials similar



to Silica. In addition to the porosity, the bioactivity of silica depends also on the pore size

(Canham et al., 1996b). As the costs of raw materials play an important role with regards to

production profits, also within pharmaceutical industry, Table 2.5 presents some characteristic

numbers for different silicon grades that can be used to produce porous silica.

Table 2.5. Industrial attributes of different Si grades

Grade of Silicon Industrial Use Purity (%) Cost ($/kg) Global Production

(tones/year)

Wafer Electronics 99.99999 1000 5000

Electronic Si Crystals 99.999 10-100 19000

Solar Solar cells 99.99 10-50 26000

Chemical Silicones 99.9 10 675000

Metallurgical Steel 97-99 1-5 1000000

Frequently in laboratory tests, when no large or pilot scale production has been realized, the

grade utilized is the one with the highest purity and cost (wafers). When scaling-up is performed,

the grade typically used for solar cells can be used without compromising the quality of the

pharmaceutical/ medical silica product. Furthermore, silicon ingots can be directly (without

making wafers from them) used for etching silica, which further reduces the production costs.

In the present introduction we focus on fabrication and (bio) pharmaceutical characterisation of

various mesoporous silicon (PSi) materials. The PSi materials are regarded “top-down” materials

on the contrary to the synthesized mesoporous molecular sieves, like “bottom-up” silica

materials, which refers to the self-assembly of silicon oxide by means of polymeric templates

determining the structure obtained. Porous silicon has some advantages compared to the silica-

based materials, but also some disadvantages, like a wider pore size distribution, which will be

described and discussed here. In addition, some new data considering drug loading, drug

dissolution/release enhancement and drug-PSi biocompatibility (cell viability, cell toxicity)

issues is compiled.

Fabrication of the various mesoporous silicon particles

The fabrication of mesoporous silicon (PSi) for drug delivery purposes can be divided in two

phases. First, the pores are produced in the silicon wafers or particles by electrochemical or stain

etching. The technique denotes the systems as ‘top-down’ nanomaterials contrary to mesoporous



molecular sieves, which are ‘bottom-up’ materials synthesized via the self-assembly of silicon

oxide by means of polymeric templates determining the structure obtained.

Top-down approach

The etching process determines the pore architecture/morphology, whereas the type of the

surface modification determines the interactions of the material with surrounding environment.

The surface modification can comprise the functionalization of the surface, e.g. for enhanced,

prolonged or targeted drug delivery purposes. However, for oral drug delivery the most

important functionalities of the surfaces are to provide high drug or therapeutic agent payloads

and to control the release of the molecules in a desired way by enhancing (or prolonging) the

dissolution behavior. The surface chemistry plays also a key role in the toxicity of the PSi

particles, since, as such, PSi degrades mainly into monomeric orthosilicic acid (Si(OH)4), which

is the natural form of Si in environment and vital for normal bone and connective tissue

homeostasis (Anderson et al., 2003). The most frequently used method to fabricate PSi is

electrochemical anodization of Si in hydrofluoric acid (HF) solutions. Anodization is controlled

either by anodic current density or voltage; the constant current method is preferred as it allows

better control of the porosity and thickness, and better reproducibility. In the simplest setup to

anodize PSi, a strip of Si and a cathode material are dipped into HF solution and an etching

current is applied between these two electrodes (Fig. 2.6). The porous layer is formed on the

surfaces of the Si strip (positive anode), typically platinum is used as the cathode, and the

fabrication cell is made of HF-resistant material. Dilute HF solutions are generally used as

electrolytes where ethanol or another surface tension reducing agent is added to reduce the

formation of hydrogen bubbles and to improve electrolyte penetration in the pores. The resultant

uniform PSi layer warrants typically also for illumination during the etching (Halimaoui 1995).

Different fabrication methods have been developed for optimized PSi fabrication (Salonen and

Lehto 2008; Kolasinski 2005; Foll et al., 2002; Splinter et al., 2001). The properties of PSi, such

as porous layer thickness, porosity, pore size, pore volume and pore shape are strongly

dependent on the fabrication conditions.



Fig 2.7. Setup scheme for electrochemical anodization to produce porous layer on Si

In the case of anodization, these conditions include HF concentration, chemical composition of

the electrolyte, current density, wafer type and resistivity, its crystallographic orientation,

temperature, etching time, electrolyte stirring, illumination intensity and wavelength, etc. The

complete control of the fabrication is complicated, but also provides a great potential to produce

different types of porous material suitable for various applications. The dopant type affects the

pore diameter so that normally with n-type Si larger and straighter pores are obtained than with

p-type Si (Levy-Clement1995). However, the dopant concentration of Si and the current density

have also major effects on the pore morphology for the p-type Si wafer. The resistivity of the

wafer decreases as the dopant concentration increases resulting in increased average pore size

and decreased specific surface area. In the highly doped substrates, like in n+- and p+ -type PSi,

the average pore size is 6–20 nm and the specific surface area 100–300 m2/g. The pores are

orientated perpendicular to the initial surface of the wafer and, in many cases; the pores are

cylindrical with smooth pore walls that are not interconnected. However, depending on the

current density and the composition of the electrolyte, branched, fir tree-type pore structures can

be produced on the highly doped wafers. Decreasing the HF concentration usually increases the

diameters of the pores formed, and the pores become smoother and straighter. Generally,

increasing the current density (i.e., anodization potential) has the same type of effect on the pores

(Halimaoui 1997; Zhang 2001; Salonen et al., 2000).

In oral drug delivery, powdered materials are normally used. After etching, the porous layer is

detached from the wafer by abruptly increasing the current density and free standing, as-

anodized porous films are obtained. The porous film can be converted into porous powder with

specific particle sizes by milling and subsequent sieving. If the average pore size of the

powdered material is to be increased, this can be realized at this stage by thermal annealing in

inert atmosphere, which causes the coarsening of the PSi structure (Björkqvist et al., 2006). The

Pt Cathode

Electrolyte

Si Anode



material must be functionalized after the comminution (or annealing), since new surfaces are

produced during milling, and the new surfaces have to be also chemically modified to obtain

homogenous material. The as-anodized PSi is hydrogen terminated consisting of Si—H, Si—H2

and Si—H3 hydrides. The simplest way to stabilize the as-anodized PSi is the partial oxidation

performed at quite mild environment (300°C, normal air condition) for a few hours. The

treatment causes a so called back-bond oxidation of PSi, where oxygen atoms selectively attack

the back-bonds of the surface Si atoms instead of replacing hydrogen atoms (Kato et al., 1988;

Salonen et al., 1997). Due to the oxidation, the surface turns from hydrophobic to hydrophilic.

Performing the oxidation above 600°C, a drastic drop in the specific surface area has been

observed (Herino et al., 1984) due to the structural expansion caused by oxidation. Several other

oxidation techniques have been reported (see references in Salonen and Lehto 2008).

Bottom up approach

This approach involves a preparation of mesoporous silica (e.g. MCM-41, SBA-15 and TUD-1)

from a silica precursor (in most cases it is TEOS: tetraethyl orthosilicate). This silica precursor is

often hydrolyzed in presence of acid or base to produce silica. In order to imprint a structure on

this silica, researchers used certain self assembled structure directing units. When these structure

directing agents are present in mesophases during the hydrolysis of TEOS the silica molecules

gets condensed around the structures and exhibits the same structure.

Table 2.6. List of various drugs tried along with different mesoporous silica

Drug Silica Pore

Volume

(cm3/g)

Pore

diameter

(nm)

Surface

area

(m2/g)

Reference

Flurbiprofen FSM-16 -- 3.98 1260 Chem. Pharm. Bull. 53(8)

974-977 (2005)

Indomethacin TOPSi 0.542 8.8 321 Molecular Pharmaceutics

7 (2009) 227-236

Telmisartan amine

functionalized

MCM41

1.54 12.9 694 Journal of Controlled

Release 145 (2010) 257-

263

Piroxicam SBA15 0.97 8.4 610 Applied Surface Science

256 (2010) 6963-6968



Piroxicam MCM41 0.65 3.21 803 Eur. J. Pharm. Sci. 32

(2007) 216-222

Itraconazole SBA15 0.77 7.9 461 Chem. Commun. 13

(2007) 1375-1377

Ibuprofen TUD1 0.556 4.9 453 Int. J. Pharm. 331 (2007)

133-138

Carbamazepine MCM41 0.66 3.3 830 Microporous and

Mesoporous Materials 113

(2008) 445-452

Drug loading of the particles

When a (therapeutic) solid material has been confined in a restricted nano-sized space (pores), its

physicochemical properties differ dramatically from the properties of the corresponding bulk

material. The space can be so narrow that any ordering of the atoms/molecules is prevented and,

thus, no lattice energy is involved. If the material is crystallized, the surface of the material forms

a major part of the confined material. In both cases, the interface of the material loaded in the

pores and the pore walls play pronounced roles with regards to the interaction of the material

with the surroundings, e.g., during drug dissolution. By alternating the pore size and the surface

chemistry towards the molecule to be loaded in the pores, the properties of the drug delivery

material can be controlled. Typically, especially at a larger scale, the loading of PSi is performed

by immersing the surface treated or functionalized microparticles into a loading solution

(Salonen et al., 2008). An advantage of this method is that the loading can be performed at room

temperature and the drug to be loaded is not exposed to harsh chemical conditions during the

loading. In the cases of protein and peptide delivery, these features might be essential. After

loading, the microparticles are filtered out from the solution and dried to obtain dry powder.

There are several factors affecting the loading process (Fig. 2.7), e.g., solvent, pH of the solution,

concentration of the solution, time scale and temperature of the loading process, the surface

termination of the pore surfaces, and the drug molecule itself.



Fig. 2.8 Three principal components of loading process affecting the obtained drug loading

degree

As it is normally desired that all the drug molecules loaded in the mesoporous carrier are located

inside the pores, it is essential to choose the loading parameters in such a way that no drug

material is crystallized on the external surface of the particles. Choosing the wrong loading

parameters, e.g. the solvent, can also cause chemical degradation of the drug during the loading

process. Fourier transform infra-red (FTIR) spectroscopy can be utilized as a fast screening

method for the degradation, but more reliable method is high performance liquid

chromatography (HPLC) that has been utilized to quantify both the loading degree and chemical

purity of the loaded porous particles. As the HPLC analyses are performed for the extracted

samples, it is essential to use solvents which dissolve all the drug material from the porous

carrier without causing any extra degradation. This is not always a trivial task and, thus, it is

beneficial to use several parallel analytical methods like nitrogen adsorption, density

measurement and thermal analysis (Salonen et al., 2005a and 2005b; Lehto et al., 2005).

Calculation of the loading degree by means of nitrogen adsorption is based on the difference in

pore volumes of the sample before and after the drug loading. This gives the estimation of the

volume of the drug in the pores, which can be turned into the mass fraction by using the density

value of the drug. By measuring the density of the drug loaded sample and comparing the value

to the corresponding values of the pure porous sample and the pure drug, the loading degree can

also be calculated. Both nitrogen adsorption and density measurements give erroneous results if

the drug blocks the pore openings preventing gas penetration into the pores. Also, both the

methods need the density value of the drug loaded in the pores, which certainly differs from to

the corresponding values of the pure porous sample and the pure drug, the loading degree can

also be calculated. If the decomposition product reacts with the surface of the carrier, erroneous

results can be obtained. To distinguish the drug material adsorbed on the external surface (in

crystalline form) from that located inside the pores, differential scanning calorimetry (DSC) can

Solvent

Drug molecule

Mesoporous silica



be employed. If there is any crystalline material present in the sample, the melting endotherm

can be observed at the same temperature as for the bulk material, and the accompanying energy

is related to the amount of the crystalline material. By subtracting the amount of the crystalline

material (DSC) from the total drug content (TG), an estimate for the drug material located inside

the pores is obtained. If this material is in amorphous form, no melting endotherm(s) can be

detected in the DSC thermograms, but if the material forms nanocrystals, a broad melting

endotherm can be detected at depressed temperatures. Typically these crystals are so small that

they cannot be detected with X-ray powder diffraction (XRPD).

Enhancement of drug dissolution and permeability

As suggested above, utilization of the mesoporous microparticles to increase the solubility and

the dissolution rate is based on the fact that the formation of crystalline material is restricted by

the confined space of the pores, which are only a few times larger than the drug molecule, thus

retaining the drug in its amorphous/noncrystalline, disordered form (Salonen et al., 2005b). In

their disordered state the compounds exhibit higher dissolution rates than their crystalline

counterparts, especially when solubility is limited by high lattice energies (Yu 2001; Huang et

al., 2004). The dissolution rates from the porous materials will also be improved by the high

surface area (up to several hundreds of m2/g) characteristic for these carrier materials. Further

benefits for the improved dissolution are obtained through improved wetting properties of the

particles (Salonen et al., 2005b). The mesoporous materials have also been shown to improve the

permeability of large, hydrophilic drug molecules in combination with oral permeation enhancers

(Foraker et al., 2003), and to provide sustained/ controlled release (Andersson et al.,

2004;Cavallaro et al., 2004; Vallet-Regi et al., 2004). In the case of controlled release carrier

function, nano-sized mesoporous particles may serve as aids to enhance the circulatory

persistence of drugs and to target the drugs to specific cells (Aston et al., 2005).

In a study conducted by Salonen et al. (Salonen et al., 2005b), mesoporous silicon (PSi)

microparticles were produced using thermal carbonization (TCPSi) or thermal oxidation (TOPSi)

to obtain surfaces suitable for oral drug administration applications. Loadings of five model

drugs (antipyrine, ibuprofen, griseofulvin, ranitidine and furosemide) into the microparticles and

their subsequent dissolution/release behaviour were studied. The loading of the drugs into TCPSi

and TOPSi microparticles showed that, in addition to the effects of stability of the particles in the



presence of aqueous or organic solvents, the surface properties of the particles determined the

compound affinity towards the mesoporous particles.

Table 2.7. Time (min) to obtain 80% of drug release at various pH.

Drug pH 7.4 pH 6.8 pH 5.5

Free Loaded Free Loaded Free Loaded

Antipyrine 45 75 -- -- -- --

Ranitidine 24 59 16 97 33 90

Ibuprofen 60 35 60 48 260 65

Griseofulvin ** 33* 364* 123* 267* 94*

Furosemide 83 41 67 65 294 69

*: time (min) to abtain 20% drug release

**: not reached during experiment

Besides the surface properties, also the chemical nature of the drug and the loading solution were

critical to the loading process. This was reflected in the obtained loading efficiencies, which

varied between 9% and 45% with TCPSi particles (Salonen et al., 2005b). The release rates of

the loaded drugs from the TCPSi microparticles were also found to depend on the characteristic

dissolution behavior of the drug substance in question. When the dissolution rate of the free/

unloaded drug was high, the microparticles caused a delayed release. However, with poorly

dissolving drugs, the loading into the mesoporous microparticles clearly improved and

accelerated dissolution (Table 2.7). Moreover, pH dependency of the dissolution was reduced

when the drug substance was loaded into the microparticles. Combined release and permeation

enhancement behavior was also recently shown for poorly soluble and poorly permeable

furosemide loaded into thermally carbonized mesoporous silicon (TCPSi) microparticles

(Kaukonen et al., 2007).

Permeation was studied across Caco-2 monolayers at pH-values of 5.5, 6.8 and 7.4, from drug

solutions and TCPSi particles (Kaukonen et al., 2007). Furosemide loaded in the TCPSi

exhibited improved dissolution from the microparticles with greatly diminished pH dependence.

At pH 5.5 (the lowest furosemide solubility), the flux of TCPSi-loaded furosemide across the

Caco-2 monolayers was over 5-fold higher compared to the pre-dissolved furosemide. The

highest furosemide permeability was observed at pH 5.5 with the Papp value from the TCPSi

microparticles 18.0 ± 1.3 × 10-6

cm/s. Also at pH 6.8 and pH 7.4 higher flux- and mesoporous



TCPSi and SBA-15, showed that in addition to the effects regarding particle stability, also the

surface properties affect significantly the compound affinity towards the particles and to drug

release (Salonen et al., 2005b). This observation presents an important potential to tailor the

surface properties accordingly to suite the compound in question.

Professor Peter Swaan’s group has studied the use of porous silicon particles in combination with

permeability enhancers in order to deliver insulin across the intestinal Caco-2 cells (Foraker et

al., 2003). A major disadvantage of permeation enhancers is the lack of specificity, which may

open up a route for food-borne pathogens and toxins to migrate along with the therapeutic

compounds. To minimize this risk, the group developed a system called OralMEDDS (Oral

Micro-Engineered Delivery Devices) that consists of novel porous silicon particles that can be

used as oral drug-delivery vehicles. Once prepared, the particles could be loaded with liquid drug

formulation through simple capillary action. Interstitial air is removed by vacuum aspiration, and

the formulation is dried using vacuum drying or freeze-drying. OralMEDDS particles are

designed to target into the intestinal epithelial cells, adhere to the apical cell surface, and deliver

the drug formulation containing a coadministered permeation enhancer that will open up the

local tight junctions of the paracellular transport pathway (Foraker et al., 2003). Absorption of

macromolecules (e.g. insulin) and hydrophilic drugs, which are unable to undergo transcellular

transport across lipid membranes like the intestinal wall, is largely restricted to the paracellular

route. Thus, the intestinal absorption of orally administered water-soluble drugs can be enhanced

through the utilization of OralMEDDs particles; the drug transport efficiency could be

augmented at least 10-fold when the drug formulations were delivered in porous silicon particles

when compared to liquid formulations, and up to 100-fold when compared to formulations

without the permeation enhancers. Further targeting and specificity could be obtained by

attaching cytoadhesive lectins specifically bound to the intestinal mucosa, as previously

demonstrated in vitro with similar microdevices by the research group of Desai (Ahmed et al.,

2002).



Carbamazepine – A Drug Profile (Sweetman, 2002)

Fig 2.9. Molecular structure of Carbamzepine

Chemical name: 5 H- Dibenz [ b,f ] azepine-5 - carboxamide (Merck, 2001)

Molecular formula: C15H12N2O

Molecular weight: 236.27

Carbamazepine was approved in the United States for use as an anti – seizure drug in 1974. It

has been employed since 1960s for the treatment of trigeminal neuralgia. It is now considered as

the primary drug for the treatment of partial and tonic – clonic seizures. Carbamazepine is a

derivative of iminostilbene with a carbamyl group at 5 position, this moiety is essential for potent

antiseizure activity.

Carbamazepine is official in IP (Indian Pharmacopoeia, 1996) and USP (The United States

Pharmacopoeia, 2007). It occurs as a white to off-white powder, practically insoluble in water

and soluble in alcohol and in acetone.

Mechanism of Action

Carbamazepine (Tripathi, 1995) limits the repetitive firing of action potential evoked by a

sustained depolarization of mouse spinal cord or cortical neurons in an in – vitro release study.

This appears to be mediated by slowing of the rate of recovery of voltage activated sodium

channels from inactivation. The effects of Carbamazepine are evident at concentrations in the

range of therapeutic drug levels in CSF in human beings. The Carbamazepine metabolite 10, 11

– epoxide also limits sustained repetitive firing at therapeutically relevant concentrations

suggesting that this metabolite may contribute to anti – seizure efficacy of Carbamazepine.



Pharmacokinetics

Carbamazepine is absorbed slowly and erratically after oral administration. Peak concentrations

are observed 4 to 8 hours after oral ingestion. Therapeutic plasma concentrations are reported to

be 4 – 12 µg/mL though considerable variations occur. The drug distributes rapidly into all the

tissues. Binding to plasma proteins occurs to the extent of 75% and the concentration in the CSF

appear to correspond to the concentration of the free drug in the plasma. It is extensively

metabolized in the liver. The predominant pathway of metabolism in humans involves the

conversion to 10, 11 – epoxide. This metabolite is as active as the parent compound in various

animals and its concentration in plasma and brain may reach 50% of those of Carbamazepine,

especially during the concurrent administration of phenytoin or Phenobarbital. The 10, 11 –

epoxide is metabolized further to inactive compounds, which are excreted in the urine principally

as glucoronides. Carbamazepine also is inactivated by conjugation and hydroxylation. Less than

3% of the drug is recovered in the urine as parent compound or as epoxide. During long term

therapy, the half – life of Carbamazepine averages between 10 and 20 hours. Because of

induction of drug metabolism enzymes, the half life is much longer in individuals who have

received a single dose. In patients, who are receiving Phenobarbital or Phenytoin, the half life is

reduced to 9 to 10 hours. Carbamazepine crosses the placental barrier and is distributed in the

breast milk.

Adverse effects

Common side effects during the initial stages of therapy include dizziness, drowsiness and

ataxia. Drowsiness and disturbances of cerebellar and oculo – motor function with ataxia,

diplopia are the symptoms of excessive plasma concentrations of Carbamazepine and may

disappear with concomitant treatment at reduced dosage. Gastro – intestinal symptoms are

reported to be less common and include dry mouth, abdominal pain, nausea, vomiting, anorexia,

diarrhea etc. Photosensitivity reactions, urticaria, exfoliative dermatitis, Stevens – Johnsons

syndrome and systemic lupus erythematosus have been reported. Occasional reports of blood

disorders include agranulocytosis, aplastic anemia, eosinophilia, persistent leucopenia and

thrombocytopenia. Other adverse effects include hyponatremia, headache, arrythmias and heart

block, heart failure, impotence, male infertility, gynaecomastia, galactorrhoea etc. Overdosage

may be manifested by many of the adverse effects listed above and may result in stupor, coma,



convulsions, respiratory depression and death. Congenital malformations have been reported to

exacerbate seizures in patients suffering from mixed type epilepsy. Congenital malformations

have been reported in infants born to women who have received Carbamazepine during therapy.

Overdosage

In case of Carbamazepine poisoning, supportive measures such as management of airways,

ventilation and monitoring of cardioavascular function and electrolyte balance are most

important. Gastric lavage may be most useful as the antimuscarinic effects of the drug delay

gastric emptying.

Precautions

Carbamazepine should be avoided in patients with atrioventricular conduction abnormalities. It

should not be given to patients with a history of bone marrow depression. Carbamazepine should

be given with caution to patients with a history of blood disorders or hematological reactions to

other drugs or of cardiac, hepatic or renal disease. Since Carbamazepine has mild anti –

muscarinic properties, caution should be observed in patients with glaucoma or raised intra-

ocular pressure etc. It should be used with care in patients on MAO Inhibitors or oral anti –

coagulants, change of treatment from Carbamazepine to other anti – epileptic drugs.

Interactions

Carbamazepine is a hepatic enzyme inducer and induces its own metabolism as well as that of a

number of other drugs including antibacterials such as doxycycline, anticoagulants and sex

hormones. Carbamazepine and Phenytoin may mutually enhance one another’s metabolism. The

metabolism of Carbamazepine is enhanced by enzyme inducers such as Phenobarbital. Alcohol

may exacerbate CNS side effects of Carbamazepine. Antidepressants may antagonize the anti –

epileptic activity of Carbamazepine by lowering the convulsive threshold. Dextropropoxyphene

has been reported to cause substantial elevation of serum Carbamazepine concentrations and

Carbamazepine toxicity probably due to inhibition of Carbamazepine metabolism.

Carbamazepine lowers both the plasma concentration and therapeutic effect of Haloperidol. It

produces neurotoxic reactions when combined with lithium. It increases risk of acetaminophen



hepatotoxicity. Azithromycin increases serum concentration of carbamazepine (Pfizer labs,

2001). Rifampicin increases carbamazepine levels and toxicity. It decreases theophylline

effectiveness by increasing metabolism by hepatic enzymes.

The bioavailability and plasma concentration of Carbamazepine have been reported to be

increased by grape fruit juice.

Therapeutic uses

FDA approved indications for Carbamazepine are: 1) It is useful in patients with generalized

tonic – clonic and both simple and complex partial seizures and 2) It reduces or abolishes pain in

trigeminal neuralgia. Non – FDA approved indications are: 1) Diabetes insipidus, central or

partial 2) Psychotic disorders.

Contraindication

Carbamazepine is contraindicated in

1. Concomitant use of monoamine oxidase inhibitors

2. Hypersensitivity to carbamazepine or tricyclic compounds

3. Patients with a history of previous bone marrow depression

Dosage and Administration

Therapy for epilepsy is usually started at a dosage of 200 mg taken twice daily to minimize side

effects. Dosage is gradually increased to 600 mg to 1200 mg per day for adults and 20 mg/kg to

30 mg/kg for children. Therapy for trigeminal neuralgia is generally started at a dose of 200

mg/day, the dose may be increased gradually as the need be to a level of 1200 mg/day, if this is

tolerated.

Chapter II-b: Mesoporous Silica: a Novel Carrier Rational and Objectives


Literature reports disclosed preparation of mesoporous silica using various structure-directing or

templating agent. Here, in the proposed study, the objective was to prepare mesoporous silica

(MS) using hydroxyl propyl-β-cyclodextrin (HPBCD) as a template. CDs were used to form

inorganic–organic mesophases via self assembly process. CDs are cyclic oligosaccharides

comprised of six to eight D-glucose units joined together by α-1,4 linkage (α-CD=6 units, β-

CD=7 units, γ-CD=8 units) CD rings are amphiphilic with broad rim displaying two and three –

OH groups and the slender rim exhibiting six –OH groups on its supple arm (Saenger et al.,

1998). These hydrophilic groups remain on the external surface of the hydrophobic molecular

cavity that is lined with ether-like anomeric oxygen atoms, thus, CD can be easily modified by

functionalization of these reactive hydroxyl groups (Croft and Bartsch, 1983). Moreover, these

relatively large number of hydroxyl group per unit area and small molecular size (1.4 to 1.7 nm)

should ideally reconcile compatibility with siloxane-based matrix precursors (with reactive Si–

OH groups) via hydrogen bonding (Yim etl al., 2003). There are several reports showing use of

CDs as alternative to classical amphiphiles as structure-directing templates for the production of

disordered porous silica materials having “worm-like” pore structures using the nano cast

method (Polarz et al., 2001).

Since the developed MS carrier exhibited a large pore volume and greater surface area we

thought to evaluate this material for solubility enhancement potential of various poorly water

soluble drugs.

Chapter II-b: Mesoporous Silica: a Novel Carrier Experimental


A. Synthesis and optimization of MS

Optimization of components

In order to select suitable quantities of water and HCl for the hydrolysis of TEOS we have carried

out blank runs. Briefly as follows:

Table 2.8. Reaction composition for TEOS hydrolysis

Reaction number Quantity of TEOS Quantity of water Quantity of HCl

R1 0.5 5 10

R2 0.5 10 10

R3 0.5 15 10

R4 0.5 5 20

R5 0.5 10 20

R6 0.5 15 20

R7 0.5 5 30

R8 0.5 10 30

R9 0.5 15 30

All the quantities are expressed in g.

These reactions were carried out in order to understand the time require for the conversion of

solution state of reaction component to form a gel state (data shown in table 2.8). This time was

observed along with the heat of reaction (in tentative manner).

Optimization of concentration of HPBCD

Table 2.9 Concentration of HPBCD in different reaction runs

Reaction number Quantity of

TEOS

Quantity of water Quantity of HCl Quantity of

HPBCD

R10 0.5 15 30 0.5

R11 0.5 15 30 1

R12 0.5 15 30 1.5

R13 0.5 15 30 2



Synthesis of MS

Two g of HPBCD was dissolved in 30 mL of distilled water; 60 mL of HCl was added and

stirring was continued to get single phase solution. To this solution, 1 g of TEOS was added. The

system was homogenized using a magnetic stirrer. Ethanol formed during the reaction was

removed under the application of reduced pressure. The stirring was continued till a thick light-

brown gel is formed. The gel was aged for 3 days in an open round-bottomed flask. HPBCD was

removed from the product by calcination at 600 °C for 6 h. The white powder was then recovered

and ground in a mortar and pestle. This material is termed as cyclodextrin imprinted MS.

B. Standardization of carbamazepine

Carbamazepine was procured from Amoli Organics, and is official in USP 2007. Various tests

were carried out to ascertain the compliance of the drug sample with pharmacopoeial and non –

pharmacopoeial standards.

Description

Organoleptic evaluation of the sample of Carbamazepine was carried out to determine the

colour, odour and the appearance.

Identification

pH of the solution

A 1% w/v solution of Carbamazepine was prepared in purified water and the pH of the

solution was recorded using a Equiptronics pH meter Model No. EQ610.

Ultraviolet/ Visible Spectrum

UV spectrum of the Carbamazepine sample was determined on a UV Spectrophotometer,

Shimadzu (UV – 1650).

Solubility studies

Excess of drug was placed in 10 mL of each USP buffer (pH 1.2, pH 4.5, pH 6.8, pH 7.4, pH

10), in duplicates. The suspensions were placed in a mechanical shaker for 48 h at 37 ± 0.5 ºC

for saturation. The suspensions were cyclomixed intermittently and were filtered after 48 h

and the amount of Carbamazepine dissolved was calculated by UV Spectrophotometry.

Particle size determination



The mean particle diameter of the sample of Carbamazepine was determined on a particle size

analyzer Malvern 2000 (Malvern, UK) working on the principle of dynamic laser light

scattering.

Density

The sample was weighed accurately (W) and introduced into a graduated glass cylinder and

leveled carefully without compacting. The unsettled apparent volume was read as Vo to the

nearest graduated unit. The bulk density was calculated in g/ml by the following formula

Bulk density = (W/Vo) ------------------------------------------------------------------------(2.6)

The cylinder was then placed on a Veego Bulk Density Testing Apparatus (USP 1) and tapped

500 times. The tapped volume was then was read as Va to the nearest graduated unit. The

tapped density was calculated in g/ml by the following formula

Tapped density = (W/Va)----------------------------------------------------------------------(2.7)

Carr’s Index

Carr’s Index or % Compressibility was calculated by the following formula:

Carr’s index or % compressibility = (Tap density - Bulk density) x 100--------------(2.8)

Tap density

Carr’s Index is indicative of the flow properties of the material. An index of 5 – 15 indicates

excellent flow properties while an index of 12 – 21 is indicative of the need of a glidant to

improve the flow. An index of 23 – 40 indicates a poor flow of the material

Hausner’s ratio

Hausner’s ratio was calculated by the following formula:

Hausner’s ratio = Tap density -------------------------------------------------------------(2.9)

Bulk density

Hausner’s ratio is indicative of the flow properties of the material. A value of between 1.25 –

1.5 is indicative of the need of a glidant to improve the flow. Values greater than 1.25

indicates poor flow (33% Carr’s) while values less than 1.25 indicates good flow (33%

Carr’s).



Acidity or alkalinity

To 1.0 g, add 20 mL of carbon dioxide-free water and shake for 15 min and filter. To 10 mL

of the filtrate add 0.05 mL of phenolphthalein solution and 0.5 mL of 0.01M sodium

hydroxide; the solution is red. Add 1.0 mL of 0.01M hydrochloric acid; the solution is

colorless. Add 0.15 mL of methyl red solution; the solution is red.

Chlorides Maximum 140 ppm.

Suspend 0.715 g in 20 mL of water and boil for 10 min. Cool and dilute to 20 mL with water.

Filter through a membrane filter (nominal pore size: 0.8 µm). Dilute 10 mL of the filtrate to

15 mL with water. This solution complies with the limit test for chlorides.

Heavy metals Maximum 20 ppm.

1.0 g complies with limit test C. Prepare the standard using 2 mL of lead standard solution

(10ppm Pb).

Loss on drying Determined on 1.000 g by drying in an oven at 100 -105 °C for 2 h.

Sulphated ash Maximum 0.1%, determined on 1.0 g.

C. Analytical method development for carbamazepine

UV Spectroscopy

Calibration curves of bicalutamide were prepared in distilled water, methanol and 1% SLS

solution. An accurately weighed amount of bicalutamide (10 mg) was transferred to 100 ml

volumetric flask. The drug was dissolved in respective media and volume was made up with the

same solvent. This stock solution was diluted to give concentrations in the linear range.

Absorbance of these solutions was measured against respective media as blank. A series of such

calibration curves were constructed and the linearity range was determined. The above

experiments were repeated in triplicate. This UV-Spectrophotometric method was used for drug

content analysis and in vitro drug release studies.

High Performance Liquid Chromatography (HPLC)



A stability indicating HPLC method was developed and validated for the determination of

drug content during stability studies. The chromatographic conditions followed were as follows:

HPLC unit : Agilent 12000 series

Pump : Agilent Quadra HPLC pump

Detector : Agilent UV detector

Column : Zorbax Eclipse® XDB – 18 (5 µm) (4.6 mm x 250 mm)

Mobile phase : Acetonitrile: methanol: water (10:60:40 v/v/v)

Flow rate : 1 ml/min

Detection : 230nm

Loop size : 20 L

Degradation studies

The drug was subjected to forced degradation under acidic conditions (1N HCl), basic

conditions (1N NaOH) and oxidation (30% H2O2) by heating at 90oC for 4 hrs. A 100 g/ml

aqueous solution was prepared and accordingly treated. These solutions were further neutralized,

diluted to final concentrations of 10g/ml with the mobile phase and injected.

Method validation

The developed HPLC method was validated for linearity, precision, recovery, limit of

detection, limit of quantification and stability of analyte.

Linearity

It is a measure of how well a calibration plot of response versus concentration

approximates a straight line.

Carbamazepine (50 mg) was accurately weighed and transferred to a 50 ml volumetric

flask. Volume was made up with methanol to obtain the primary stock. This stock was suitably

diluted with same solvent to obtain concentrations in the range of 1µg/ml to 20µg/ml. These

individual solutions were then injected into the HPLC system. The peak areas were calculated and

plotted against respective concentrations. A series of such calibration curves were constructed and



the linearity range was determined. The coefficient of correlation was also computed. The above

experiments were repeated in triplicate.

Precision

Instrumental precision (repeatability)

Sequential, repetitive injections (n=3) of the same sample of 10 µg/mL concentration was

carried out followed by averaging the peak areas and determination of % C.V. of all injections.

Intra assay precision

Solutions with 5 µg/mL concentrations from 3 different weighing were injected. Relative

standard deviation of the data gave a measure of accuracy of the method.

Inter day precision

Duplicate analysis of 5 µg/ml samples on 2 different days was carried out and %C.V. was

determined.

Ruggedness

A solution of 5 g/ml was analyzed at intervals of 0, 8, and 24 hours, storing the samples

at room temperature. The samples were checked for, whether there is any peak corresponding to

the degradation products.

Limit of detection (LOD)

LOD was determined by first examining the noise of the instrument by injecting the

mobile phase in triplicates and finding values with the highest and lowest peak areas at a range

covering the retention time of the drug, 6 -10 mins. The difference in the areas gave the noise of

the instrument. Peak area having three times the noise gave an estimate of the LOD.

Limit of quantification (LOQ)

It is the smallest concentration of analyte, which gives a response that can be accurately

quantified. Noise of the instrument was determined as given above and the peak area having ten

times the value of noise gave an estimate of the LOQ.



Assay

To determine the content of carbamazepine from the tablets, 20 tablets were weighed and

crushed. The mix powder equivalent to 10 mg of carbamazepine was weighed accurately and

transferred to a 100 ml of volumetric flask. Methanol was used for extraction. To ensure complete

extraction of drug, solution was sonicated to 20 minutes and the volume was made up to 100ml.

The resulting solution was centrifuged and the supernatant was diluted with the mobile phase and

injected. The analysis was repeated in triplicate. The assay was reported under results and

discussion of stability studies.

Drug loading on MS

Carbamazaepine was used as a drug candidate for loading on MS in various ratios as shown in

table 2.10. The drug was dissolved in acetone (10 mL) followed addition of predefined quantity of

MS was then added to the solution. The system was stirred till the complete evaporation of

acetone. The solid material left was collected, sifted, and dried overnight at 60 °C. These CBZ-

MS particles were used for further physicochemical evaluation and tablet formulation.

Table 2.10. Batch composition of CBZ and MS

Drug loaded on MS batch number Quantity of CBZ (mg) Quantity of MS (mg)

CBZ-MS 1 50 100

CBZ-MS 2 100 100

CBZ-MS 3 150 100

CBZ- MS 4 200 100

Dissolution studies of these samples were carried out in 900 mL 1% SLS solution in USP type II

dissolution test apparatus operated at 75 rpm and maintained at 37 °C. Sink condition was

maintained throughout the study. Ten milliliters of sample was collected at each time point and

analyzed after suitable dilution with dissolution medium using UV spectrophotometer at 287 nm.

D. Characterization

Fourier-transform infrared analysis



Fourier-transform infrared analysis (FTIR) studies were performed using Spectrum 100 (Perkin

Elmer, USA) to determine the presence of functional groups and evaluation of chemical entities.

Attenuated total reflectance method was used. Samples were mixed with KBr in ratio of 1:100.

Thirty-two scans were performed with a resolution of 4 cm−1.

Scanning electron microscopy

The morphology of MS and CBZ-MS was examined by scanning electron microscopy (JSM-

6380LA, Jeol, Japan). The samples were sputtered with gold and palladium using a vacuum

evaporator and examined at 15 kV accelerating voltage.

Transmission electron microscopy

High-resolution transmission electron microscopy (TEM) images were generated for MS and

CBZ-MS using Philips CM200 (Philips, UK) at 200 kV. The samples were initially dispersed in

water and then placed on a porous carbon film on copper grid. The sample was then air-dried

before proceeding for TEM analysis.

Thermal analysis

The physical state of neat CBZ and CBZ-MS was characterized by differential scanning

calorimetry (DSC). These measurements were carried out in a DSC (Pyris 6 DSC, Perkin Elmer,

USA). A sample equivalent to 5 mg of CBZ was accurately weighed and sealed in aluminum pan.

The measurements were performed under nitrogen purge over (20 mL/min) at 30– 220 °C at a

heating rate of 10 °C/min. An empty pan was used as reference and for calibration prior to each

experiment.


Neat CBZ and CBZ-MS were evaluated using Rigaku diffractometer (Miniflex, Japan) Cu-Kα

radiation. The samples were run over the most informative range from 0° to 60° of 2θ. The step

scan mode was performed with a step size of 0.02° at a rate of 2°/min.

Nitrogen sorption analysis



BET (Brunauer–Emmett–Teller) surface area, pore volume and pore diameter of MS was

measured using ASAP2020 (Micromeritics, USA). Before initiation of the study, the sample was

degassed in a degas port for 6 h` at 200 °C. The nitrogen adsorption isotherm was recorded at

−196 °C under liquid nitrogen temperature. The estimation of pore volume and diameter was done

by BJH (Barrett–Joyner– Halenda) model.

Tablet formulation

CBZ-MS tablets were prepared (with the composition as shown in table 2.11) by direct

compression method on a single punch compression machine. 8 mm circular, standard concave

punches were used for compression. The crushing strength of tablets was maintained within 6–8

kg/cm2.

Table 2.11. Composition of CBZ-MS tablets

Content mg/tab

CBZ-MS 200

Microcrystalline cellulose (MCC 102) 82

Sodium starch glycolate (Glycolys) 15

Colloidal silica (Aerosil 200) 3

Total 300

In vitro dissolution studies

CBZ-MS tablets, Tegrital® and neat CBZ were subjected to dissolution studies. The dissolution

test was carried out using USP type II dissolution test apparatus, with 900 mL of 1 % SLS

solution as dissolution medium, at 37 °C. The paddle speed was maintained at 75 rpm (USP 28,

2005). Sink condition was maintained throughout the study. Ten milliliters of sample was

collected at each time point and analyzed after suitable dilution with dissolution medium using

UV spectrophotometer at 287 nm.

In vivo studies

In vivo studies were carried out in mice. Proper 12-h dark/light cycle was maintained throughout

their housing period. Use of these animals for the study was approved by the Animal Ethics

Committee of the Institute of Chemical Technology, Mumbai. The mice were fasted overnight

prior to the study. Animals were divided into four groups, each group contained six mice. All

doses were administered through oral route. Group A received 0.5 mL of vehicle (0.25 % sodium



carboxy methyl cellulose), group B received Tegrital® equivalent to CBZ of 35 mg/kg of body

weight suspended in 0.5 mL of vehicle, group C got neat CBZ 35 mg/kg of body weight in 0.5

mL vehicle and group D is administered with CBZ-MS formulation equivalent to 35 mg/kg body

weight (Tayel et al., 2008), suspended in 0.5 mL of vehicle. Maximal electroshock method was

used to induce hind limb extensor phase. The animals were restrained by hand and an electric

current was applied post 1 h dosing, by placing electrodes on their ears. A current of 15 mA of

frequency 50 Hz is applied for 0.2 s. The animals were observed for the presence of hind limb

extension. The animals were designated as protected if they fail to show hind limb extensor phase.

The overall activity of the groups was expressed as percent protection.

E. Stability studies

The purpose of stability studies is to provide evidence on how the quality of a drug

substance varies with time under the influence of a variety of environmental factors such as

temperature, humidity and light and enables recommended storage conditions and shelf life to be

established.

To carry out these studies, the formulation was subjected to 25°C/60% relative humidity

(R.H), 30°C/65% R.H and 40°C/75% R.H as per the stability protocol (table 2.12). Samples were

charged in stability chambers (Thermolab, India) with humidity and temperature control. They

were drawn at specified intervals for analysis over a period of 6 months. Drug content of the

tablets was analyzed using previously developed and validated stability indicating HPLC method.

Table 2.12. Stability Protocol for CBZ-MS tablets

PRODUCT NAME: CARBAMAZEPINE TABLETS

BATCH NO. CBZ-MS 1:1 Tablet

APPEARANCE white tablets

TOTAL NO SAMPLE (INCLUDING INITIAL) 400 tablets

QUANTITY FOR PHYSICAL/ CHEMICAL ANALYSIS 90 tablets

DATE OF STABILITY STARTED 06/2011

REGION FOR TESTING - 6 months (stability testing as per ICH guidelines)



F. Further trials with other drug candidates

The developed mesoporous silica was also evaluated for different drug candidates, through a

process of solvent loading and checked for, whether there is any significant improvement in drug

release or not.

Chapter II-b: Mesoporous Silica: a Novel Carrier Results and Discussion


A. Synthesis and optimization of MS

Optimization of components

The preparation of mesoporous silica in ‘bottom up’ synthesis approach is preferably done

through liquid silica precursor (silica source). In the present work we have used TEOS as silica

precursor. The silica is obtained from the liquid source through a process of acidic or basic

hydrolysis. Therefore, we have utilized combination of HCl and water as hydrolyzing machinery

for the reaction system, and of course HPCD played a role of structure director for the

mesoporosity in the resultant product.

Optimization of water and acid for hydrolysis

Table 2.13. Effect of water-acid mixture on reaction time and exothermic behavior

Reaction number Time required for sol-gel conversion (min) Heat of the reaction mixture

R1 120 +++

R2 180 ++

R3 250 +

R4 90 ++++

R5 120 +++

R6 140 ++

R7 30 +++++

R8 40 ++++

R9 60 ++

From the blank reactions runs it was easy to conclude that smaller quantities of HCl require more

time for the sol to gel conversion of silica precursor TEOS. The least possible time was observed

in R9 run. Therefore we have finalized R9 as our reaction condition. Mixing of acid with water

always results in evolution of heat. This could possibly be a cause of concern for safety aspects

when there is no provision of cooling systems or one wants to carry the reaction at room

temperature. Therefore a tentative evaluation of reactions run for exothermic behavior showed an

acceptable heat tolerance with respect to R9 with least possible reaction time.

Optimization of concentration of HPBCD



The hydrolysis of silica precursor was supposed to be carried out in presence of HPBCD.

Therefore, we thought to evaluate the maximum quantity of HPCD that could be dissolved easily

in the given reaction composition in order to achieve maximum mesoporosity.

Table 2.14. System observation with respect to different concentration of HPBCD in reaction

mixture

Reaction number Observation

R10 Clear system, HPBCD dissolved completely

R11 Clear system

R12 Certain fraction remains undissolved, requires sonication for complete

dissolution

R13 Not clear

Fabrication through a sol–gel process using HPBCD as a template is expected to give non-

ordered porous material in which every pore is expected to demonstrate geometry of HPBCD.

Depending upon the concentration, mesoporosity would be gained by a molecular percolation

process at equivalent volume fractions of template to water but still a non-ordered pore system

would be obtained. In general, it is accepted that increase in surface area lead to enhanced mass

transfer during the process of dissolution (Li et al., 2011). Hydrogen bonding and steric

hindrance are more often used to explain the stabilizing performance (Dinuzio et al., 2008).

Molecular structure of CBZ has carbonyl group as strong hydrogen bond acceptor and silanol

group of silica acts as hydrogen bond donor (Se-Hyun et al., 2011) resulting in steric hindrance

thereby preventing further aggregation and particle size growth.

B. Standardisation of Carbamazepine

Table 2.15. Showed the stardization parameters for carbamazepine drug.

Table 2.15. Standardization parameters for carbamazepine

Test Results Limits

1. Description White colored powder,

odorless and tasteless

White colored powder,

odorless and tasteless

2. Identification



Melting point

IR Absorption

193°C*

Complies*

189 – 193°C

IR of the sample is

concordant with that

Carbamazepine RS

3. pH of 1% w/w solution 7.11 – 7.12 Not reported

4. Ultraviolet/ Visible

Spectrum

10 µg/mL (Methanol)

λmax at 284 nm

Not reported

5. Solubility pH 1.2 – 0.222 mg/mL

pH 4.5 – 0.218 mg/mL

pH 6.8 – 0.202 mg/mL

pH 7.4 – 0.208 mg/mL

Water – 0.256 mg/mL

Not reported

6. Particle size

Determination

Mean particle diameter

267 microns

Not reported

7. Density

Bulk density

Tap density

0.607 g/cm3

0.759 g/cm3

Not reported

8. Carr’s Index 20.02 % Not reported

9. Hausner’s Ratio 1.26 Not reported

10. Acidity or Alkalinity Complies* To comply

11. Chlorides Passes* Not more than 140

ppm

12. Related substances

10,11 Dihydrocarbamazepine

Iminodibenzyl

Single Max unknown impurity

Total impurity

0.02 %*

Nil*

0.04 %*

0.05 %*

Not more than 0.1%

Not more than 0.1%

Not more than 0.1%

Not more than 0.5%

13. Sulphated ash 0.032 %* Not more than 0.1%

14. Heavy metals Passes* Not more than 20 ppm



15. Loss on Drying 0.27 %* Not more than 0.5%

16. Intrinsic Dissolution in

Dissolution media

256 mg dissolved at the

end of 24 hours

Not reported

17. Assay 99.88 % of

C15H12N2O on dried

basis*

98 % to 102% on dried

basis

* - Results from the certificate of analysis

C. Analytical method development for carbamazepine

UV spectroscopy

For routine analysis a UV spectrophotometric method was developed with following parameters.

Table 2.16. UV spectrophotometric analytical parameters for carbamazepine

UV method Purified water 1% w/v sodium lauryl sulphate

solution

Methanol

Linearity 0 µg/mL to 20

µg/mL 0 µg/mL to 20 µg/mL

0 µg/mL to 20

µg/mL

Wavelength 284 nm 287 nm 284 nm

Slope 0.0513 0.0502 0.0503

Correlation

coefficient 0.9999 0.9998 0.9999

y - Intercept 0.00008 ± 0.0005 0.0042 - 0.0005

High Performance Liquid Chromatography (HPLC)

Degradation studies

The chromatographic conditions were optimized in order to obtain a good separation

between drug and its degradation products. The chromatograms confirmed that carbamazepine

degrades in extreme conditions of pH, oxidation and heat.



(a)

(b)

(c)



(d)

(e)

(f)

Fig. 2.10. HPLC chromatogram of a: standard carbamazepine, b: acid degraded, c: base

degraded, d: heat degraded, e: light degraded, and f: oxidated carbamazepine



Method validation

The developed HPLC method was validated for linearity, precision, limit of detection,

limit of quantification and stability of analyte, as shown in following table.

Table 2.17. Validation Parameters for HPLC analysis of carbamazepine

Linearity

Linearity range: 1 to 20 ppm

Line equation: y = 74.519x + 34.512

Correlation Coefficient: 0.9992

Instrumental precision

(Repeatability)

Mean AUC±SD: 782±8

%RSD:1.023

Intraday precision Mean AUC±SD: 782.66±5.686

%RSD:0.726

Inter-day precision Mean AUC±SD: 778.33±4.274

%RSD: 0.549

Ruggedness

0 hour Mean AUC±SD: 782±3

%RSD:0.384

8 hours Mean AUC±SD: 776±7.549

%RSD: 0.973

24 hours Mean AUC±SD: 776±9.644

%RSD:1.243

LOD 189.24 ng/mL

LOQ 0.631 µg/mL

Drug loading on MS

It was clear from the fig.2.11 that increase in carrier quantity would lead to rapid release of CBZ

as there would be more surface area provided by the carrier to the drug which would positively

be used for the interaction with the dissolution medium. However CBZ: MS in a proportion of

1:1 would seem to be enough to impart a significant improvement of the dissolution of CBZ.

Therefore for further development CBZ-MS2 was finalized.



Fig. 2.11 Dissolution profile of CBZ from various particulate systems.

D. Characterization

Fourier-transform infrared spectroscopy

Neat CBZ FTIR spectrum (Fig. 2.12a) showed its characteristic peaks at 1129 cm−1 (C–N

stretching), 1605 cm−1 (N–H, primary amide bending), 1677 cm−1 (C=O carbonyl stretching),

and 1600 (C=C stretching) 725 cm−1, 765 cm−1, 800 cm−1 and 870 cm−1 (C–H bending with

ring puckering). The presence of a peak at 3161 cm−1 signifies that CBZ is in its polymorphic

form III (Grzesiak et al., 2003]. FTIR spectrum (fig. 2.12b) showed peaks for MS 970 cm−1 for

Si–OH stretch (Bae et al., 2006). The presence of an 810 cm−1 peak also supports the same. Si–

O–Si siloxane exhibited by 1,092 cm−1 absorption band (Anderson, 1974). In case of CBZ-MS

(fig. 2.12c), two important observations were: (1) absorption peak intensities were found to be

low as compared to neat CBZ and (2) the C– H absorption values also changed from 765 to 767

cm−1 and from 800 to 795 cm−1 indicating that there may be interaction between two moieties.

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70

Dru

g R

ele

ase

d (

%)

Time (Min)

CBZ-MS1

CBZ-MS2

CBZ-MS3

CBZ-MS4



Fig. 2.12 FTIR spectrum of a: neat CBZ, b: MS and c: CBZ-MS

Scanning electron microscopy

Neat CBZ showed shiny surface as seen in Fig. 2.13a. The crystalline particles of CBZ found to

be conglomerated. This may be to achieve lesser surface energy and higher stability (Mokkapati

et al., 2006). MS (Fig. 2.13b) particles exhibited no agglomeration. They found to have larger

surface area for interaction. The physical mixture (Fig. 2.13c) showed a blend of CBZ and MS

particle where some of the CBZ particles adhered to the surface of MS particles. CBZ-MS (Fig.

2.13d) showed completely masked appearance of CBZ crystals indicating that the CBZ is either

at the surface of MS or within the pores of MS.



Fig. 2.13. Scanning electron microscopy images of a: neat CBZ, b: MS, c: physical mixture of

CBZ and MS, and d: CBZ-MS

Transmission electron microscopy

TEM was performed to investigate pore structures within MS particles. The sample was initially

dispersed and well mixed in water and followed by placement on TEM grid. A good quality of

contrast between the non-ordered but uniform worm-like mesoporous channels and silica matrix

is observed for MS particles as seen from fig. 2.14a. Images of CBZ-MS (fig. 2.14b) revealed the

presence of CBZ within the pores of MS, as indicated by darker dots.

(a) (b)

Fig. 2.14. Transmission electron microscopic images of a: MS and b: CBZ-MS

Thermal studies

DSC is often used to investigate crystal types and their transition with temperature. Physical

mixture of CBZ and MS (fig. 2.15a) showed that CBZ remained in crystalline state as CBZ

showed an observable endothermic peak. A broadened melting point for Tegrital® (fig. 2.15b)



was observed. Neat CBZ (fig. 2.15c) showed melting at 175 °C and recrystallization to “form I”

followed by another melting of “form I” at 193 °C. This thermal behavior is well in agreement

with literature and concluded to be CBZ crystalline “form III” (Grzesiak et al., 2003). Melting

endotherm of CBZ vanished in CBZ-MS (fig. 2.15d) system, signifying loss of crystalline state

of CBZ. MS showed inert thermal behavior and remained almost unaffected to the temperature

change. Very subtle peak observed for MS from 80 to 100 °C pointing towards moisture loss.

Fig 2.15 . DSC thermogram of a: physical mixture of CBZ and MS, b: Tegrital®, c: neat CBZ,

d: CBZ-MS, and e: MS


X-ray diffraction pattern of neat CBZ and MS loaded with CBZ are shown in Fig. 2.17. MS (fig.

2.16a) was proved to be in amorphous state as indicated by the presence of a background bump

in powder X-ray diffraction (PXRD). Background bump is often indicative of non-crystalline

composition of material whereas peak position describes the phases present in the sample. XRD

of CBZ (fig. 2.16e) displayed peaks at 2θ values of 13.14, 13.71, 15.03, 15.36, 15.93, 17.17,

18.69, 19.56, 20.56, 22.07, 23.45, 25.00, 26.40, 27.47, 29.44, and 30.08 signifying presence of

polymorphic form III of CBZ which is in good agreement with literature values (Grzesiak et al.,

2003). Neat CBZ showed very narrow crystal size as indicated by low peak width. The

background bump in the XRD pattern corresponding to noncrystalline nature of the compound

was found to be progressively increasing from neat CBZ, physical mixture of CBZ and MS (fig.

2.16c) to CBZ-MS system (Fig. 2.16b). The amorphous systems are in relatively high energetic



state which plays an important role for higher solubility as compared to their corresponding

crystalline counterpart (Corrigan et al., 1984).

Fig 2.16 . PXRD of a: MS, b: CBZ-MS, c: Physical mixture of CBZ and MS, d: Tegrital® and e:

neat CBZ

Nitrogen sorption studies

Nitrogen adsorption and desorption behavior of MS is shown in fig. 2.17a along with pore size

distribution plot (fig. 2.17b). Specific surface area calculated from BET method was found to be

480.37 m2/g. Pore diameter of MS calculated by desorption branch from BJH method (DBJH)

was found to be 5.8 nm. Total pore volume of all the pores was found to be 0.8041 cm3/g as

calculated from single point adsorption method at partial pressure of 0.974. A typical type IV

sorption isotherm is displayed when MS is subjected to nitrogen sorption studies. The curve also

showed nitrogen condensation step which is distinct feature of mesoporous materials (Hui et al.,

2010).

0

500

1000

1500

0 10 20 30 40 50 60

0

500

1000

1500

0 10 20 30 40 50 60

0

2000

4000

6000

0 10 20 30 40 50 60

0

5000

10000

0 10 20 30 40 50 60

01000020000300004000050000

0 10 20 30 40 50 60

2θ

b

c

d

e

aIn

ten

sity



(a)

(b)

Fig. 2.17. a: Nitrogen adsorption isotherm for MS and b: pore size distribution plot

In vitro dissolution

Comparative dissolution kinetics of CBZ from different systems is shown in fig. 2.18.

Significantly improved drug release profile was observed for CBZ-MS when compared with neat

CBZ. Approximately 80 % of drug release is achieved within 10 min with CBZ-MS. This may

be due

to increased surface area of CBZ, improved wettability and reduced crystallinity of CBZ in CBZ-

MS system. Due to geometric confinement of CBZ within the mesopores of MS, it remained

0

100

200

300

400

500

600

0 0.2 0.4 0.6 0.8 1

Volu

me A

dso

rb

ed

(cc/g

ST

P)

Relative Pressure



difficult for CBZ to aggregate and crystallize. Thus, this confinement maintained CBZ molecules

in high-energy state and served a driving potential for spontaneous dissolution.

Fig. 2.18. Dissolution profile of CBZ from in house and marketed formulation

In vivo anticonvulsant activity

The in vivo anticonvulsant activity exhibited by mice against MES is shown in table 2.21. The

animals of group A were not found to be protected against MES spread, whereas neat CBZ

showed a limited protection for MES spread. Both Tegrital® and CBZ-MS were found to exhibit

complete absence of hind limb extensor phase in all the animals. This may be due to a rapid

dissolution profile and improved solubility of CBZ.

Table 2.18. Anticonvulsant activity of various formulations

Group Number Number of animals exhibiting convulsion Protection (%)

A 6/6 Zero

B 0/6 100

C 4/6 33.33

D 0/6 100

E. Stability studies

Stability studies were performed on the optimized formulation CBZ-MS (1:1) tablets. The assay,

friability hardness, disintegration and dissolution pattern was found to be acceptable. With

respect to these parameters a successful stability studies were done and the formulation was

found to be stable upon storage. Since the formulation was found to be in accelerated conditions

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70

Dru

g R

ele

ase

(%

)

Time (min)

Tegrital Tablet

Neat CBZ

CBZ-MS Tablet



thus an assumption for the stability and subsequently shelf life of formulation can be made for a

period of two years in real time.

Table 2.19. Stability data of CBZ-MS tablets.

Storage condition Time (months) Assay (%) Friability (%) Disintegration

(seconds) Hardness (kg/cm2)

Initial 0 101.57 0.105 43 7.5

25 oC/ 60% RH 1 100.7 0.124 45 6.8

25 oC/ 60% RH 2 100.49 0.179 49 6.5

25 oC/ 60% RH 3 101.34 0.187 57 6.5

25 oC/ 60% RH 6 101.79 0.230 62 6.2

30 oC/ 65% RH 1 102.54 0.110 42 7.6

30 oC/ 65% RH 2 100.4 0.107 48 7.2

30 oC/ 65% RH 3 100.6 0.234 46 6.7

30 oC/ 65% RH 6 100.98 0.297 57 6

40 oC/ 75% RH 1 101.69 0.149 57 7.6

40 oC/ 75% RH 2 100.89 0.157 54 6

40 oC/ 75% RH 3 99.29 0.197 59 6.1

40 oC/ 75% RH 6 101.57 0.267 65 5

Table 2.19 showed the stability data. The tablets were found to be stable upon storage as per ICH

guidelines. There was no significant change in drug content of the formulation and the

dissolution profile was found to remain unaltered.



(a)

(b)

(c)

Fig 2.19. Dissolution profile of carbamazepine from stability samples of CBZ-MS tablets stored

at a: 25 oC/ 60% RH b: 30

oC/ 65% RH and c: 40

oC/ 75% RH

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70

Dru

g R

ele

ase

d (

%)

Time (Min)

CBZ-MS Tablet (Initial)

1 Month

2 Months

3 Months

6 Months

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70

Dru

g R

ele

ase

d (

%)

Time (Min)


1 Month

2 Months

3 Months

6 Months

0

20

40

60

80

100

120

0 10 20 30 40 50 60 70

Dru

g R

ele

ase

d (

%)

Time (Min)


1 Month

2 Months

3 Months

6 Months



F. Further trials with other drug candidates

The developed carrier has also been checked for its solubility enhancement of potential as

follows:

Table 2.20. Physicochemical attributes of letrozole

Physicochemical attribute Remark

Name of drug Letrozole

Dose 2.5 mg

Molecular weight 285.303

Molecular formula C17H11N5

logP 2.5

pKa 1.6 (monoprotonated form)

Indication Metastatic breast cancer

Melting point 184°C

Brand name Femara Tablet

Dissolution condition 500mL 0.1 N HCl, USP type II dissolution apparatus, 75 rpm and

37°C.

Solubility in water 0.799 mg/L

Fig 2.20. Dissolution profile of letrozole at different levels of drug loading

0

20

40

60

80

100

120

0 10 20 30 40 50 60

Dru

g R

ele

ase

(%

)

Time (Min)

Neat LTZ

LTZ:MS 1:1

LTZ:MS 1:2

LTZ:MS 1:3



Table 2.21. Physicochemical attributes of bicalutamide


Name of drug Bicalutamide

Dose 50 mg


Molecular formula C18H14F4N2O4S

logP 2.7

pKa 11.94 (predicted)

Indication Prostate cancer


Brand name Casodex Tablet

Dissolution condition 1000mL 1% SLS, USP type II dissolution

apparatus, 50 rpm and 37°C.

Solubility in water 5 mg/L

Fig.2.21. Dissolution profile of bicalutamide at different levels of drug loading

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70

Dru

g R

ele

ase

(%

)

Time (Min)

BCL:MS 1:1

BCL:MS 1:2

BCL:MS 1:3

BCL:MS 1:4



Table 2.22. Physicochemical attributes of itraconazole


Name of drug Itraconazole

Dose 100 mg


Molecular formula C35H38Cl2N8O4

logP 5.66

pKa 3.7

Indication Fungal infections


Brand name Sporanox capsule

Dissolution condition Simulated gastric fluid, USP type II

dissolution apparatus, 100 rpm and 37°C.

Solubility in water Insoluble, 9.64mg/L

Fig. 2.22. Dissolution profile of neat and loaded itraconazole

0

5

10

15

20

25

0 20 40 60 80 100

Dru

g R

ele

ase

(%

)

Time (Min)

Neat Itz

MS:Itz 1:1



Table 2.23. Physicochemical attributes of carvedilol


Name of drug Carvedilol

Dose 25 mg


Molecular formula C24H26N2O4

logP 4.19

pKa 14.03, 8.04(predicted)

Indication Hypertension

Melting point 114-115°C

Brand name Coreg tablet

Dissolution condition Simulated gastric fluid without enzyme, USP type II dissolution

apparatus, 50 rpm and 37°C.

Solubility in water 0.583 mg/L

Fig. 2.23. Dissolution profile of carvedilol at different levels of drug loading

0

20

40

60

80

100

0 20 40 60 80 100 120 140

Dru

g R

ele

ase

(%

)

Time (Min)

Car:MS 1:5

Neat Car

Car:MS 1:1

Chapter II-b: Mesoporous Silica: a Novel Carrier Conclusion


Conclusion

A facile method is presented for the fabrication of generic class of carrier. This carrier can be

used to develop a platform technology for solubility enhancement of BCS class II drugs.

Improved dissolution profile from CBZ-MS was obtained. CBZ was found to be in non-

crystalline state in CBZ-MS system due to geometric confinement within the pores of MS. Both

in vitro and in vivo performances of CBZ from CBZ-MS were found to be comparable with that

of marketed formulation.

Chapter II-b: Mesoporous Silica: a Novel Carrier References


References

Ahmed, A.; Bonner, C.; Desai, T. A. Bioadhesive microdevices with multiple reservoirs: a new

platform for oral drug delivery. Journal of Controlled Release 2002, 81, 291-306.

Anderson, S. H. C.; Elliot, H.; Wallis, D. J. Dissolution of different forms of partially porous

silicon wafers under simulated physiological conditions. Physica Status Solidi (a) 2003, 197,

331-335.

Anderson, D. R. Analysis of siloxanes, Smith AL, editor, Wiley Interscience, New York, 1974,

Chapter 10.

Andersson, J.; Rosenholm, J.; Areva, S. Influences of material characteristics on ibuprofen drug

loading and release profiles from ordered micro and mesoporous silica matrices. Chemistry of

Materials 2004, 16, 4160-4167.

Aston, R.; Saffie-Siebert, R.; Canham, L. Nanotechnology applications for drug delivery.

Pharmaceutical Technology 2005, 17, 21-28.

Bae, J. Y.; Choi, S. H.; Bae, B. Preparation and optical characterization of mesoporous silica

films with different pore sizes. Bulletin of Korean Chemical Society 2006, 27, 1562–1567.

Björkqvist, M.; Paski, J.; Salonen, J. Studies on hysteresis reduction in thermally-carbonized

porous silicon humidity sensor. IEEE Sensors Journal 2006, 6, 542-547.

Canham, L. T.; Reeves, C. L.; King, D. O. Bioactive polycrystalline silicon. Advanced Materials

1996a, 8, 850-852.

Canham, L. T.; Newey, J. P.; Reeves, C. L. The effects of DC electric currents on the in-vitro

calcification of bioactive silicon wafers. Advanced Materials 1996b, 8, 847-849.

Canham, L. T.; Reeves, C. L.; Newey, J. P. Derivatized mesoporous silicon with dramatically

improved stability in simulated human blood plasma. Advanced Materials 1999, 11, 1505- 1507.

Canham, L. T. Bioactive silicon structure fabrication through nanoetching techniques. Advaced

Materials 1995, 7, 1033-1037.

Carbamazepine, Department of Health and Social Services for Northern Ireland, 2007.

Carbamazepine, The United States Pharmacopoeia (USP-30)/The National Formulary (NF- 25)

United States Pharmacopoeia Convention, Inc. 12601 Twinbrook parkway, Rockville, MD.

2007.

Carbamazepine, Indian Pharmacopoeia, Vol. I and II, Ministry of Health and Family welfare,

Government of India, Controller of Publication, Delhi, 1996, 137.



Cavallaro, G.; Pierro, P; Palumbo, F. S. Drug delivery devices based on mesoporous silicate.

Drug Delivery 2004, 11, 41-46.

Corrigan, O. I.; Holohan, E. M. Amorphous spray-dried hydroflumethiazidepolyvinylpyrrolidone

Systems: physicochemical properties. Journal of Pharmacy and Pharmacology 1984, 36, 217–

221.

Croft, A. P.; Bartsch, R. A. Synthesis of chemically modified cyclodextrins. Tetrahedron 1983,

39, 1417–1474.

Dinuzio, J. C.; Miller, D. A.; Yang, W.; Mcginity, G. W.; Williams, R. O. Amorphous

compositions using concentration enhancing polymers for improved bioavailability of

itraconazole. Molecular Pharmaceutics 2008, 5, 968–980.

Foll, H.; Christophersen, M.; Carstensen, J. Formation and applications of porous silicon.

Material Science and Engineering: R: Reports 2002, 39, 93–141.

Foraker, A. B.; Walczak, R. J.; Cohen, M. H. Microfabricated porous silicon particles enhanced

paracellular delivery of insulin across intestinal Caco-2 cell monolayers. Pharmaceutical

Research 2003, 20, 110-116.

Grzesiak, A. L.; Lang, M.; Kim, K.; Matzger, A. J. Comparison of the four anhydrous

polymorphs of carbamazepine and the crystal structure of Form I. Journal of Pharmaceutical

Sciences 2003, 92, 2260–2271.

Halimaoui, A. Porous silicon formation by anodization. In: Properties of Porous Silicon, Canham

L (Ed.), Short Run Press Ltd., London, 12, 1997.

Halimaoui, A. Material processing, properties and applications. In: Porous Silicon Science and

Technology, Vial JC and Derrien J (eds.), Springer-Verlag, 1995, 33-52.

Herino, R.; Perio, A.; Barla, K. Microstructure of Porous silicon and its evolution with

temperature. Material Letters 1984, 2, 519-523.

Horcajada, P.; Ramila, A.; Perez-Pariente, J.; Influence of pore size of MCM-41 matrices on

drug delivery rate. Microporous and Mesoporous Materials 2004, 68, 105-109.

Huang, L. F.; Tong, W. Q. T. Impact of solid state properties on developability assessment of

drug candidates. Advanced Drug Delivery Reviews 2004, 56, 321-334.

Hui, C. W.; Jiang, T. L.; Pei, L.; Xia, B. L.; Xiao, B. B.; Xiao, M. W. Low temperature strategy

to synthesize high surface area mesoporous hydroxy propyl-β-cyclodextrin based silicas via

benign template removal. Microporous and Mesoporous Materials 2010,134,175–180.



Kato, Y.; Ito, K.; Hiraki, A. Oxidation properties of silicon nitride thin films fabricated by

double tubed coaxial line type microwave plasma chemical vapor deposition. Japanese Journal

of Applied Physics 1988, 27, 1401-1405.

Kolasinski, K. W. Silicon nanostructures from electroless electrochemical etching. Current

Opinion in Solid Sate and Materials Sciences 2005, 9, 73-83.

Lehto, V. P.; Vähä-Heikkilä, K.; Paski, J. Use of thermoanalytical methods in quantification of

drug load in mesoporous silicon microparticles. Journal of Thermal Analysis and Calorimetry

2005, 80, 343–397.

Levy-Clement, C. Characteristics of porous n-type silicon obtained by photoelectrochemical

etching. In: Porous Silicon Science and Technology, Vial JC and Derrien J (eds.), Springer-

Verlag. 1995, 329–344.

Li, C.; Li, C.; Le, Y.; Chen, J. Formation of bicalutamide nanodispersion for dissolution rate

enhancement. International Journal of Pharmaceutics 2011, 404, 257–263.

Mokkapati, S. P. Simulation of particle agglomerates using dispersive particle dynamics, MSc

Thesis, Texas A and M University, USA, Dec. 2006.

Polarz, S.; Smarsly, S.; Bronstein, L.; Antonietti, M. From cyclodextrin assemblies to porous

materials by silica templating. Angewandte Chemie International Edition 2001, 40, 4417–4421.

Product Information: Zithromax, Azithromycin. Pfizer Labs, NY, 2001.

Saenger, W.; Jacob, J.; Gessler, K.; Steiner, T.; Hoffmann, D.; Sanbe, H. Structures of common

cyclodextrins and their larger analogues beyond the doughnut. Chemical Reviews 1998, 98,

1787–1802.

Salonen, J.; Lehto, V. P.; Laine, E. Thermal oxidation of free-standing porous silicon films.

Applied Physics Letter 1997, 70, 637–639.

Salonen, J.; Björkqvist, M.; Laine, E. Effects of fabrication parameters on porous p+-type silicon

morphology. Physica Status Solidi (a) 2000, 182, 249-254.

Salonen, J.; Paski, J.; Vähä-Heikkilä, K. Determination of drug load in porous silicon

microparticles by calorimetry. Physica Status Solidi (a) 2005a , 202, 1629–1633.

Salonen, J.; Laitinen, L.; Kaukonen, A. M. Mesoporous silicon microparticles for oral drug

delivery: Loading and release of five model drugs. Journal of Controlled Release 2005b, 108,

362– 374.



Salonen, J.; Kaukonen, A. M.; Hirvonen, J. Mesoporous silicon in drug delivery applications.

Journal of Pharmaceutical Science 2008, 97, 632-653.

Salonen, J.; Lehto, V. P. Fabrication and chemical surface modification of mesoporous silicon

for biomedical applications. Chemical Engineering Journal 2008, 137,162-172.

Se-Hyun, S.; Hyung-Il, K. Contribution of hydrogen bond and coupling reaction to improvement

in compatibility of organic polymers/ silica nanocomposites. Journal of Industrial and

Engineering Chemistry 2001, 7, 147–152.

Splinter, A.; Sturmann, J.; Benecke, W. New porous silicon formation technology using internal

current generation with galvanic elements. Sensors and Actuators A 2001, 92, 394–399.

Tayel, S. A.; Soliman, I. I.; Louis, D. Improvement of dissolution properties of carbamazepine

through application of liquisolid tablet technique. European Journal of Pharmaceutics and

Biopharmaceutics 2008,69, 342–347.

The Merck Index, Thirteenth Edition, Carbamazepine, Merck Research Laboratories, 2001, 298.

Sweetman, S.C. Anti epileptics, Carbamazepine, Martindale – The Complete Drug Reference,

Thirty third Edition, Pharmaceutical Press, 2002, 342 – 347.

The United States Pharmacopoeia National Formulary, USP28 NF23, The United States

Pharmacopoeial Convention, Canada, 2005, pp. 342, 343

Tripathi, M.D. CNS Drugs – Anti epileptics, Essentials of Medical Pharmacology, Delhi

Publications House, 1995, 386 – 387.

Vallet-Regi, M.; Doadrio, J. C.; Doadrio, A. L. Hexagonal ordered mesoporous material as a

matrix for the controlled release of amoxicillin. Solid State Ionics 2004, 172,435-439.

Yim, J. H.; Lyu, Y. Y.; Jeong, H. D; Song, S. A.; Hwang, I. S.; Hyeon-lee, J. et al. The

preparation and characterization of mesopores in siloxane based materials that use cyclodextrins

as template. Advanced Functional Materials 2003, 13, 382–386.

Yu, L. Amorphous pharmaceutical solids: preparation, characterization and stabilization.

Advanced Drug Delivery Reviews 2001, 48, 27-42.

Zhang, G. Electrochemistry of Silicon and its Oxides, Kluwer Academic Publishers, Secauces,

NJ, USA, 2001.

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