Introduction

There is a growing awareness of the importance of disease state and drug action in chronopharmaceutics and chronopharmacology. The time-controlled and pulsa-tile release is increasingly being considered as desirable modes of drug delivery (Bussermar et al., 2001; Youan, 2004; Chaudhari et al., 2007). At present the drug must be administered in the right amount at a proper rate and at the right time for many drugs including anti-asthmatic, anti-histaminic, psychotropic, anesthetic, cardiovascular, and NSAIDS (Lemmer, 1992). Significant daily variations in pharmacokinetics or drug effects have been demon-strated in man. Depending upon the physiological and pathophysiological changes of circadian rhythmicity, nocturnal symptoms and overnight decrements in lung functions are a common part of the asthma clinical syn-drome (Lemmer, 1992). Circadian changes are seen in

normal lung function, which reaches a low point in the early morning hours. The dip is particularly pronounced in people with asthma, because bronchoconstriction and exacerbation of symptoms vary in a circadian fash-ion. Asthma is well controlled with oral corticosteroids, theophylline (TP), and β

2 agonists (Sutherland & Nalson,

1996).For such conditions a drug delivery system adminis-

tered at bed time, but releasing drug during morning hours would be ideal one (Tekade & Gattani, 2009). Pulsatile unit formulations with suitable lag time were developed in recent days for betterment of the patient (Kadam & Gattani, 2009; Rane et al., 2009). The recent interest in multiple-unit dosage forms is the result of the advantages they offer over the single-unit systems. Multiple-unit dosage forms offer more predictable gastric emptying, less dependent on the state of nutrition, less variance in transit time through the gastrointestinal tract (GIT), a higher degree of dispersion

Drug DeliveryDrug Delivery, 2010; 17(5): 343–351

2010

343

351

Address for Correspondence: Dr Surendra G. Gattani, Department of Pharmaceutics and Quality Assurance, R. C. Patel Institute of Pharmaceutical Education and Research, Near Karwand Naka, Shirpur 425 405, Dist. Dhule, Maharashtra, India. Tel: (+91) 09970816927. Fax: (+91) 02563-255189. Email: sggattani@rediffmail.com

26 November 2009

05 March 2010

09 March 2010

1071-7544

1521-0464

© 2010 Informa UK Ltd

10.3109/10717541003762821

R E S E A R C H A R T I C L E

Development of colon targeted multiparticulate pulsatile drug delivery system for treating nocturnal asthma

Vinayak D. Kadam, and Surendra G. Gattani

Department of Pharmaceutics and Quality assurance, R. C. Patel Institute of Pharmaceutical Education and Research, Near Karwand Naka, Shirpur, Dist. Dhule, Maharashtra, India

AbstractThe aim of the present study was to develop theophylline fast release enteric-coated pellets as a pulsatile drug delivery to the colon. The novelty of this work is the combination of pH and time-dependant enteric polymers as a single coating for the development of multiparticulate formulation. Theophylline pellets were optimized by applying a 2-factors 3-levels full factorial design. Continuous dissolution studies were carried out in simulated gastric, intestinal, and colonic fluid with pH 1.2 (0.1 N HCl), pH 7.4 and pH 6.8 (phosphate buffer), respectively. The lag time prior to the drug release was highly affected by combination of two fac-tors, i.e. the percentage of Eudragit RL100 in polymer mixture and coating level. The formulation containing Eudragit RL100 and Eudragit S100 with a ratio of 4:1 and coating level of 12%w/w was found to be optimum. The results of serum study in New Zealand rabbits showed that the developed formulation provided a sig-nificant lag phase of 5 h. The present study demonstrates that the theophylline enteric-coated pellets could be successfully colon targeted by the design of pH- and time-dependant modified chronopharmaceutical formulation. In conclusion, pulsatile drug release over a period of 3–12 h is consistent with the requirements for chronopharmaceutical drug delivery.

Keywords: Nocturnal asthma; colon targeted; pulsatile drug delivery; multiparticulate; factorial design

DRD

476804

(Received 26 November 2009; revised 05 March 2010; accepted 09 March 2010)

ISSN 1071-7544 print/ISSN 1521-0464 online © 2010 Informa UK LtdDOI: 10.3109/10717541003762821 http://www.informahealthcare.com/drd

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344 Vinayak D. Kadam and Surendra G.Gattani

in the digestive tract, less absorption variability, and a lesser risk of dose dumping than single-unit dosage forms (Kramer & Blume, 1994; Nykanen et al., 2001).

Various pharmaceutical approaches that have been used for targeting drug to the colon are mainly based on pH-dependant, time-dependant, and/or bacterially degradable systems (Watts & Illum, 1997; Chourasia & Jain, 2003). Among these approaches, pH-dependant systems are simple, but the suitability of them for using alone as a colonic delivery in different physiological and pathological conditions in GIT has been doubtful (Ashford et al., 1993, Ibekwe et al., 2008, Schellekens et al., 2008). Therefore, the pH-dependant system was evaluated in combination with time-dependant system in order to alleviate the pH dependency of former system and to ensure drug release under different physiological con-ditions. The use of pH-dependant and time-dependant polymers as coating materials for colonic drug delivery has been reported previously. In those studies sustained release and pH-dependant polymers have been applied as separate coating layers on top of each other (Gupta et al., 1993; Fukui et al., 2000; Qi et al., 2003). The combination of time- and pH-dependant polymer as a single coating has been used to provide the pulsatile drug release in the unit formulation (Kadam & Gattani, 2009). There is no report on the use of mixtures of these two kinds of polymers as a single or in combination coating system for the develop-ment of a multiparticulate drug delivery system.

The objective of the present study was to optimize the formulation consisting of Eudragit® RL100 (ERL®), a time-dependant polymer, and Eudragit® S100 (ES®), a pH-dependant polymer for the coating of TP pellets to achieve the colon-targeted drug delivery system (CTDDS).

It has been nicely shown that in nocturnal asthma, evening dosing of TP or β-agonists can be of advantage in treating the asthma attacks (Bose et al., 1987). TP was used as a model drug due to its suitable pharmacokinetic properties for colonic delivery and good absorption in the large intestine (Staib et al., 1986; Paola et al., 2003).

Materials and methods

Materials

TP was a kind gift from Aarti chemicals Ltd (Mumbai, India). Microcrystalline cellulose spheres (Celphere CP 203, 150-300 mesh) and hydroxy propyl cellulose (HPC-L) were supplied as free gift sample from Signet Chemical Corporation Pvt. Ltd. (Mumbai, India). ERL® and ES® were obtained from Rohm Pharma (Gmbh, Germany). Triethylcitrate (TEC) and dichlorometh-ane (DCM) was supplied as a gift sample from Merck (Germany). Isopropyl alcohol (IPA) was obtained from Loba Chemicals (Mumbai, India). Other ingredients such

as lubricants and glidants used to prepare the pellets were of standard Pharmacopoeial grade.

Methods

Experimental designTo optimize the formulation, the 32 design was imple-mented. The independent variables were ratio of ES to ERL (X

1) and percentage coating level (X

2). The dependent

variables (responses) were lag time (Y1) and drug release in

7 h in 6.8 pH buffer (Y2). The independent and dependent

variables and the used levels are summarized in Table 1. The resulting formulations are listed in Table 2.

Preparation of drug-layered pelletsDrug-loaded pellets were prepared by a spray-drying technique. TP was homogeneously dispersed in an aqueous solution of HPC-L while stirring with a mag-netic stirrer. The drug dispersion was passed through a 100 mesh sieve. The drug dispersion was then sprayed on celphere seeds using the fluidized bed coater, bot-tom spray (Miniglatt, Glatt GmbH, Binzen, Germany) with a 0.5 mm nozzle at a feed rate of 0.5–3 g/min using a peristaltic pump. The spraying process with the drug dispersion was continued to achieve the target drug load-ing level. The drug-loaded pellets were finally dried at 45°C for 15 min and were used for further coating with acrylic polymers. The composition of the drug-loaded pellets and the other processing parameters utilized for the spray-drying method are listed in Tables 3 and 4, respectively.

Enteric coating of pelletsSix per cent (w/w) solutions of polymethacrylates (ERL® and ES®) were prepared in IPA:DCM (7:3) mixture. Based on the experimental design, the detailed composition of different batches was given in Table 5. The solution was plasticized with TEC (15%, w/w, with respect to dry polymer), and then talc was added as a glidant (5%, w/w, related to dry polymer). Forty-five grams of TP pellets were coated in a fluidized bed coating apparatus (Wurster insert, Werner Glatt). Coating conditions are listed in Table 4. Samples of coated pellets were removed from the apparatus when the coating load had reached 6, 12, and 18% (w/w). At each stage the pellets were gently fluidized for ∼ 10 min.

Table 1. Independent and dependent variables and the levels used for factorial design.

Factors (independent variables)

Levels used Responses (dependent variables)1 0 −1

X1 = ratio of Eudragit S

100 to Eudragit RL 1000%

(1:0)20% (1:2)

40% (1:4)

Y1 = lag time (h)

X2 = percentage coating

level6 12 18 Y

2 = drug release in

7 h (%)

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Pulsatile drug delivery for nocturnal asthma 345

Dissolution studiesDissolution study of drug loaded pellets. To verify how the dissolution media interferes with drug release pro-file from the cores or drug loaded pellets, in vitro release behavior of cores was studied. Accurately weighed drug layered pellets equivalent to 200 mg of TP were trans-ferred to the dissolution medium.

The test was carried out in a USP dissolution type I assembly (Electrolab, TDT-08L, India) at a rotation speed of 100 rpm in 900 ml medium at 37°C for 1 h in media with pH 1.2 (0.1 N HCl), pH 7.4 and pH 6.8 (phosphate buffer). The 5 ml aliquots of the dissolution fluid were removed at specified time intervals and assayed for the amount of TP by spectrophotometer (Shimadzu, UV 1700, Japan) at wavelength 271 nm (Akhgari et al., 2005).Dissolution studies of enteric coated pellets. Accurately weighed enteric-coated pellets equivalent to 200 mg of TP were transferred to the dissolution medium. The test was carried out in a USP dissolution type I assembly (Electrolab, TDT-08L, India) at a rotation speed of 100 rpm

in 900 ml medium at 37°C in media with pH 1.2 (HCl 0.1 N), pH 7.4 and pH 6.8 (phosphate buffer) for 2 h, 3 h, and the remaining 7 h, respectively. The 5 ml aliquots of the dissolution fluid were removed at specified time intervals and assayed for the amount of TP by spectrophotometer (Shimadzu, UV 1700, Japan) at wavelength 271 nm for all three media (Zahirul, 1999; Gang et al., 2004; Akhgari et al., 2005; 2006; Mastiholimath et al., 2007; Siepmann et al., 2008; Kadam & Gattani, 2009; Tekade & Gattani, 2009).

Scanning electron microscopy (SEM)SEM (JEOL JSM-6360A scanning electron microscope, Japan) has been used to examine the surface morphology and texture of drug layered and polymer-coated pellets. Pellets were sputter-coated with platinum to a thickness of ∼ 30 nm for 6–7 min in a coating machine (Gupta et al., 2001; Rao & Patil, 2007).

Differential scanning calorimetry (DSC)The possibility of any interaction between TP, polymers, and other excipients was assessed by DSC (Mettler Toledo Stare DSC 822c, Germany). The thermogram of the samples were obtained at a scanning rate of 10°C/min conducted over a range of 0–350°C under an inert atmos-phere flushed with nitrogen at a rate of 20 ml/min.

Statistical analysis of dataThe effects of independent variables upon the responses were modelled using a second order polynomial equa-tion. The mathematical model of the effects of inde-pendent variables upon the dependent variables was performed using Stat-Ease Design Expert (Version 7.1.6) with a manual linear regression technique. A significant term (p < 0.05) was chosen for final equations. Finally, response surface plots resulting from equations were drawn.

Y b b X b X b X X b X b X0 1 1 2 2 12 1 2 11 12

22 22= + + + + +

(1)

where Y is the dependent variable, b0 is the arithmetic

mean response of the nine runs, and bi (b

1, b

2, b

12, b

11, and

b22

) is the estimated coefficient for the corresponding fac-tor X

i (X

1, X

2, X

1X

2, X

12, and X

22), which represents the aver-

age result of changing one factor at a time from its low to high value. The interaction term (X

1X

2) shows how the

response changes when two factors are simultaneously changed. The polynomial terms (X

12 and X

22) are included

to investigate non-linearity. All nine batches of design have shown wide variation in lag time and percentage drug release in 7 h (3–12 h and 8–99%, respectively). The fitted equations relating the response Y

1 and Y

2 to

the transformed factor are shown in equations (2) and (4), respectively. A backward elimination procedure was adopted to fit the data into different predictor equations.

Table 2. Composition of experimental formulations (runs).

Variable factors

X1 (Eudragit S:Eudragit RL ratio) X

2 (Coating level) (%)

1 1:4 6

2 1:4 12

3 1:4 18

4 1:2 6

5 1:2 12

6 1:2 18

7 1:0 6

8 1:0 12

9 1:0 18

Table 3. Composition of drug-loaded celphere pellets.

Composition mg/capsule

Cores

Celphere CP 203 45

Solids in layering dispersion

Theophylline 200

HPC L 60

Water qs.

Total 305

q.s.- 6 % W/W aqueous solution was prepared

Table 4. The process parameter of the drug layering processes and polymer coating on Glatt.

Process parameter Drug layering Polymer coating

Inlet temperature (°C) 50–55 45–50

Product temperature (°C) 45–47 35–36

Fluidization air (bar) 0.40–0.60 0.40–0.60

Suspension spray rate (g/min) 0.5–3 0.5–3

Atomization pressure (bar) 0.40–0.60 0.40–0.60

Nozzle diameter (mm) 0.5 0.5

Drying in the equipment after layer-ing (min)

15 10

Yield calculated after processing (%) 90 80–85

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346 Vinayak D. Kadam and Surendra G.Gattani

The quadratic model generated by regression analysis were used to construct the three dimensional graphs in which the response parameter Y was represented by a curvature surface as a function of X. Numerical optimiza-tion using desirability approach was employed to locate the optimal setting of the formulation variables to obtain the desired response.

In-vivo studySix male New Zealand white strain rabbits, weighing 2.1−2.6 kg, were used for study. Animals were housed in a 12-h light-dark, constant temperature environment prior to study. All rabbits were fasted for 24-h before the experiment. For treatment with TP, rabbits were given a vehicle (glycofurol, 2 ml/kg) right before TP administration. TP was given as an aqueous suspen-sion (8 mg/ml) at a dose of 25 mg/kg. Blood samples (1 ml) were withdrawn via right ear vein at 0, 0.25, 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, and 12 h after administration of TP. The blood was centrifuged for 15 min at 9860 x g and the serum samples obtained were stored at –20°C until analysis.

Assay methodThe TP concentration in serum was determined according to the previously reported HPLC method (Hui et al., 2001). Sample was prepared by adding 400 μl of acetonitrile solution containing 5.0 μg/ml of internal standard to 100 μl of serum. Caffeine was used as the internal standard. After being vortexed for 30 s and then centrifuged at 9860 x g for 15 min, the clear supernatant was transferred to another micro-tube and evaporated to dryness by blow-ing nitrogen. The residue was reconstituted with 100 μl of mobile phase, and 20 μl of this solution was subjected to HPLC analysis. The mobile phase used was methanol and water (20:80, v/v) with a flow rate of 1.0 ml/min. An UV detector was set at 270 nm. The HPLC apparatus included one pump and a detector. The assay employed an ODS-2 column (4.6 × 250 mm, 5 μm).

Results and discussion

Fundamental structure of the coated pellets

The drug-layered and polymer-coated TP pellets were successfully developed using Glatt fluidized bed bottom spray-coating systems. In the coating step, the drug load-ing process had an efficiency of ∼ 90% and ∼ 80–85% in polymeric coating. The loss of coated product occurred due to the formation of some agglomerates and fines in the product bed, and the loss of coating solids to exhaust. The basic structure of the film-coated pellets has been schematically shown in Figure 1. The release profile of drug-layered pellets at pH 1.2, 7.4, and 6.8 is shown in Figure 2. There was more than 90% drug release in less than 10 min. This demonstrates that, despite the poor water solubility, layering of the drug on the surface of pellets results in increased dissolution rate of drug. This is one advantage of multi-particulate systems of poorly water-soluble drugs compared to single unit systems (Akhgari et al., 2005). The drug-loaded pellets were coated with polymeric layer successively using a solvent coating technique. The polymeric layer was the water insoluble ERL and ES. The purpose of this layer was to act as a barrier to any premature drug release from the delivery system prior to reaching the colon and to provide an appropriate lag phase. It was expected to be a reasonably hydrophobic layer with drug release being controlled by the thickness of the layer.

In order to simulate the pH changes along the GI tract, three dissolution media with pH 1.2, 7.4, and 6.8 were sequentially used, referred to as sequential pH change method (Gang et al., 2004; Mastiholimath et al., 2007). At pH 1.2 (simulating stomach) none of the formula-tions released their drug content up to 2 h. In order to determine the levels of factors which yield optimum dissolution responses, mathematical relationships were generated between the dependent and independent variables.

Table 5. Composition of experimental formulations.

ES:ERL(1:4) ES:ERL(1:2) ES:ERL(1:0)

6% 12% 18% 6% 12% 18% 6% 12% 18%

A B C D E F G H I

Drug layered pellets (mg) 305 305 305 305 305 305 305 305 305

ERL (mg) 14.64 29.28 43.92 12.2 24.4 36.6 — — —

ES (mg) 3.66 7.32 10.98 6.09 12.2 18.3 18.3 36.6 54.9

TEC (mg) 2.74 5.49 8.23 2.74 5.49 8.23 2.74 5.49 8.23

IPA (mg) 200.69 401.38 602.07 200.69 401.38 602.07 200.69 401.38 602.07

DCM (mg) 86.01 172.01 258.03 86.01 172.01 258.03 86.01 172.01 258.03

Total wt. of enteric-coated pellets (mg)

323.3 341.6 359.9 323.3 341.6 359.9 323.3 341.6 359.9

Lubrication talc (2.5%) (mg)

8.08 8.54 8.99 8.08 8.54 8.99 8.08 8.54 8.99

Total wt. of lubricated pellets (mg)

331.38 350.14 368.89 331.38 350.14 368.89 331.38 350.14 368.89

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Pulsatile drug delivery for nocturnal asthma 347

The equations of the responses are given below:

Final equation in terms of coded factors:•

Final equation in terms of actual factors:•

Final equation in terms of coded factors:•

Final equation in terms of actual factors:•

The equation represents the quantitative effect of independent variables (X

1 and X

2) upon the responses

(Y1 and Y

2).

Analysis of variance (ANOVA) (Table 6) indicated the assumed regression models were significant and valid for each considered responses. The three-dimensional response surfaces were plotted to estimate the effect of independent variables on each response (Figures 3 and 4).

Figure 3 shows the effect of two formulation factors on lag time and indicates that increase in ratio of ES rises lag time significantly. ERL is a copolymer of ethyl acrylate, methyl methacrylate, and a low content of a methacrylic acid ester with quaternary ammonium groups (trimethy-lammonioethyl methacrylate chloride). The ammonium groups are present as salts and make the polymers per-meable. ES is a copolymer of methacrylic acid and methyl methacrylate, and the ratio of carboxyl to ester group is ∼ 1:2. Lower ratio of carboxyl group in ES causes less ioni-zation in neutral to alkaline media than ERL, and hence shows slower solubilization (Chourasia & Jain, 2003). Also ERL has good swelling properties than ES and Eudragit ERS (Kadam, 2009). The effect of coating thickness on lag time is lesser at low levels of ES and rises at a higher ratio (Figure 3). However, by using proper combinations of ES, ERL, and coating level, the release of drug from formula-tion after an optimum lag time will be ensured. This is an advantage for using the combination of polymers against using a single polymer (ES) which sometimes does not release drug at all (Watts & Illum, 1997). A numerical optimization technique using the desirability approach was employed to develop a new formulation with the desired responses. Constraints were applied to the fac-tors (X

1 and X

2) and (Y

1 and Y

2) for optimizing the desired

formulation. The optimized formulation was evaluated for lag time and percentage drug release after 7 h. The values of predicted and observed responses are shown in Table 7. The drug release profiles of different enteric coated formulations were given in Figure 5. According to the design the best area for formulation to obtain desired responses was found. The best conditions to optimize drug release corresponded to a ratio of ES:ERL (1:4) and a coating level of 12%. By substituting X

1 and X

2 by the

amounts of optimized formulation in equations (3) and (5), predicted responses were obtained. In order to check the validity of the optimization procedure, a new batch of pellets with the predicted levels was prepared. The result shows that the observed responses were inside the constraints and close to predicted responses, and, there-fore, factorial design is valid for predicting the optimum formulation (Table 7).

The pellets were prepared according to optimum for-mulation and released no drug at pH 1.2 (0.1 N HCl), pH 7.4, and showed burst release at pH 6.8.

Scanning electron microscopy (SEM)

Figure 6 shows SEM of optimum formulation (a) drug lay-ered (85×), (b) drug layered (3000×), (c) polymer coated

Eudragit RL-S

Celphere

Drug + HPC-L

Figure 1. The basic structure of the film-coated pellets.

Time (min)

% D

rug

Rel

ease

00

20

40

60

80

−20

100

10 20 30 04 50 60

0.1N HCI pH7.4 PB pH6.8 PB

Figure 2. Dissolution profile of drug layered pellets at pH 1.2, 7.4, and 6.8.

Y x X

X X

1 lag time in pH 6.8 7.67 2.5 1 1.8 * 2

1.00 * * 2 0.83 *

( ) = + − + +

+

λ

112

Y1

lag time 9.33333 0.30833 * ratio of

polymers + 0.138,89 *

( ) = − %

% ccoating level +

8.333,33 * ratio % oof polymers* coating

level + 2.0

%

88333 ratio of polymers2%

Y X

X X

2 % Drug release in 6.8 34.89 28.17 1

23.50 2 20.50X1 * 2

( ) = + −

−

Drug release

in pH 6.812.722,22 3.458,33 *

ratio of polyme

%= +

rrs 0.5 * coating level0.170,83 ratio of polymers * coating le

− % −% vvel

(2)

(3)

(4)

(5)

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348 Vinayak D. Kadam and Surendra G.Gattani

(85×), and (d) polymer coated (3000×s). The drug layered pellet surface (Figure 6a and b) became smoother after polymeric coating (Figures 6c and d).

Differential scanning calorimetry (DSC)

The DSC thermogram shows a sharp endothermic peak at 269.95°C for TP (Figure 7a). While in final optimum formulation, the endothermic peak was observed at 266.95°C (Figure 7b). Evaluation of the thermogram revealed no interaction between the polymer and drug in the formulation.

In-vivo evaluation of optimum formulation

The in vivo serum study was performed to see if the colon-targeted release functions of the CTDDS could

Table 6. Analysis of variance (ANOVA) of dependent variables.

Source of variation Sum of squares Degree of freedom Mean square F-ratio p-value Prob > F

Analysis of variance for Y1 (lag time in h)

Model 63.055 4 15.763 126.111 0.0002 significant

A-A 37.5 1 37.5 300 0.0001 significant

B-B 20.166 1 20.166 161.333 0.0002 significant

AB 4 1 4 32 0.0048 significant

A^2 1.3888 1 1.3888 11.111 0.0290 significant

Residual 0.5 4 0.125 — — —

Total 63.555 8 — — — —

Analysis of variance for Y2 (% drug release in 6.8)

Model 9,754.667 3 3251.556 12.962 0.0086 significant

A-A 4,760.167 1 4760.167 18.976 0.0073 significant

B-B 3,313.5 1 3313.500 13.209 0.0150 significant

AB 1,681 1 1681 6.701 0.0489 significant

Residual 1,254.222 5 250.844 — — —

Total 11,008.89 8 — — — —

Coating level (%)Polymer ratio

1:00.00

lag

time

(h)

3.1

5.3

7.5

9.7

11.9

1:21:3

1:4 6:009:00

12:0015:00

18:00

Figure 3. Response surface plot for Y1 response (lag time).

Coating level (%)

1:31.4

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g re

leas

e pH

6.8

buf

fer (

%)

0

27.5

55

82.5

110

1:21:1

1:0 18:0015:00

12:009:00

6:00

Polymer ratio (ES:ERL)

Figure 4. Response surface plot for Y2 response (% release in 7 h).

Table 7. Observed and predicted values for the optimum formulation.

Response parameters

Constrains set

Predicted values

Observed values

Residual

Ratio of polymers In range 40 (4:1) 40 (4:1) 0

% coating level In range 12 12.07 ± 0.13 0.07

Lag time in pH 6.8 6 h 5.99 6 0.01

Drug release in at 7 h

Maximize 63.05 87 ± 1.52 23.95

0

% D

rug

rele

ase

0.00

20.00

40.00

60.00

80.00

100.00

2 4 6Time (h)

8 10 12 I

H

G

F

E

D

C

B

A

Figure 5. The drug release profile of different enteric-coated formulations.

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Pulsatile drug delivery for nocturnal asthma 349

work in the GIT as expected and shows a lag phase of 6 h. To minimize the variation of gastric pH, male New Zealand white rabbits were used for this study. The aver-age pH in rabbit’s stomach has been reported to be ∼ 1.9 (Smith, 1965; Illet et al., 1990), 6–8 in small intestine, and 7.2 in colon (Karali, 1995). Serum concentration vs time profiles of TP after the administration was shown in Figure 8. Pharmacokinetic parameters necessary for discussion, calculated from the serum drug concentra-tion vs time profiles using kinetica 5 software, are listed in Table 8.

When the TP enteric-coated pellets were administered, a lag time of 5 h was obtained before serum concentration could be detected. The peak serum concentration was achieved within 6 h of administration, showing thereby that TP was immediately absorbed from the rabbit GIT. The time of onset of drug release can therefore be con-sidered close to the time of appearance of drug in the serum. From the in-vivo study it is concluded that the colon-targeted polymer-coated pellets did not release any significant amount of drug in 5 h and shows burst release in 6 h.

Conclusion

The present study concludes that the TP enteric-coated pellets could be successfully colon targeted by the design of pH and time-dependant modified chronopharmaceu-tical formulation. The formulation can be easily opti-mized by using the factorial design. Pulsatile drug release over a period of 3–12 h, consistent with the requirements for chronopharmaceutical drug delivery, was achieved from enteric-coated pellets. Thus, the designed device can be considered as one of the promising formulation technique for preparing a colon-specific pulsatile drug delivery system and hence in chronopharmaceutical management of asthma by opening a new chapter of life to an existing drug molecule.

A C

DB

A & B-Drug layered pellet C & D-Polymer coated pellet

Figure 6. Surface morphology of drug and polymer-coated pellets.

40 60 80 100 120 140 160 180 200 220 240

B

AIntegral 339.08 mJ

onset 269.29°cPeak 269.95°c

normalized -142.47Jg^-1

Integral -103.94 mJ

onset 268.83°cPeak 266.95°c

normalized -51.97Jg^-1Integral -46.01 mJ

onset 62.21°cPeak 98.63°c

normalized -23.00 Jg^-1

260 280 300 320 340

METTLER TOLEDO STAR SYSTEM

Figure 7. DSC thermogram of TP (a) and optimum formulation (b).

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350 Vinayak D. Kadam and Surendra G.Gattani

Declaration of interest

Mr Vinayak D. Kadam immensely thanks the Council of Scientific and Industrial Research, New Delhi for pro-viding Senior Research Fellowship [08540(0001)/2009-EMR-I] during his PhD work. The authors are thankful to Mr Sachin S. Kushare for his support in the experimen-tal design. The authors are thankful to Aarti Chemicals and Rohm Pharma for providing the free samples of theophylline and Eudragits®, respectively.

References

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Time (h)

Con

cent

ratio

n (m

cg/m

l)

00123456789

101112

1 2 3 4 5 6 7 8 9

Figure 8. The serum concentration vs time profiles of TP after the administration.

Table 8. Pharmacokinetic parameters obtained after oral adminis-tration of TP ER-coated optimum formulation in rabbits at a dose of 25 mg/kg.

PK parameter Theophylline enteric-coated formulations

Cmax

(ng/ml) 10.203 ± 1.1

Tmax

(h) 6.00

Tlag

(h) ∼ 5.00d

d Graphically determined by extrapolating the initial linear portion of plasma drug concentration vs time data to the x-axis.

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