Therapeutic Function: AntiinflammatoryChemical Name: m-Benzoylhydratropic acidCommon Name: 2-(3-Benzoyiphenyl)propionic acidStructural Formula:

Trade Name Manufacturer Country Year IntroducedProfenid Specia France 1973Zaditen Sandoz Japan 1983

Raw MaterialsEthanol(3-Benzoylphenyl)acetonitrileSulfuric acidSodiumMethyl iodide

Manufacturing Process

In an initial step, the sodium derivative of ethyl (3-benzoylphenyl) cyanoacetate is

prepared as follows: (3-benzoylphenyl)acetonitrile (170 9) is dissolved in ethyl carbonate

(900 g). There is added, over a period of 2 hours, a sodium ethoxide solution [prepared

from sodium (17.7 g) and anhydrous ethanol (400 cc)], the reaction mixture being heated

at about 105° to 115°C and ethanol being continuously distilled. A product precipitates.

Toluene (500 cc) is added, and then, after distillation of 50 cc of toluene, the product is

allowed to cool. Diethyl ether (600 cc) is added and the mixture is stirred for 1 hour. The

crystals which form are filtered off and washed with diethyl ether (600 cc) to give the

sodium derivative of ethyl (3-benzoylphenyl)cyanoacetate (131 g). Then, ethyl methyl(3-

benzoylphenyl)cyanoacetate employed as an intermediate material is prepared as follows:

The sodium derivative of ethyl (3-benzoylphenyl)cyanoacetate (131 g) is dissolved in

anhydrous ethanol (2 liters). Methyl iodide (236 g) is added and the mixture is heated

under reflux for 22 hours, and then concentrated to dryness under reduced pressure (10

mm Hg). The residue is taken up in methylene chloride (900 cc) and water (500 cc) and

acidified with 4N hydrochloric acid (10 cc). The methylene chloride solution is decanted,

washed with water (400 cc) and dried over anhydrous sodium sulfate. The methylene

chloride solution is filtered through a column containing alumina (1,500 g). Elution is

effected with methylene chloride (6 liters), and the solvent is evaporated under reduced

pressure (10 mm Hg) to give ethyl methyl(3-benzoylphenyl)cyanoacetate (48 g) in the

form of an oil.

In the final production preparation, a mixture of ethyl methyl(3-

benzoylphenyl)cyanoacetate (48 g), concentrated sulfuric acid (125 cc) and water (125

cc) is heated under reflux under nitrogen for 4 hours, and water (180 cc) is then added.

The reaction mixture is extracted with diethyl ether (300 cc) and the ethereal solution is

extracted with N sodium hydroxide (300 cc). The alkaline solution is treated with

decolorizing charcoal (2 g) and then acidified with concentrated hydrochloric acid (40

cc). An oil separates out, which is extracted with methylene chloride (450 cc), washed

with water (100 cc) and dried over anhydrous sodium sulfate. The product is concentrated

to dryness under reduced pressure (20 mm Hg) to give a brown oil (33.8 g). This oil is

dissolved in benzene (100 cc) and chromatographed through silica (430 g). After elution

with ethyl acetate, there is collected a fraction of 21 liters, which is concentrated to

dryness under reduced pressure (20 mm Hg). The crystalline residue (32.5 g) is

recrystallized from acetonitrile (100 cc) and a product (16.4 g), MP 94°C, is obtained. On

recrystallization from a mixture of benzene (60 cc) and petroleum ether (200 cc), there is

finally obtained 2-(3-benzoylphenyl)propionic acid (13.5 g), MP 94°C.

1256

CRYSTALLIZATION OF KETOPROFEN IN PRESSURE SENSITIVE ADHESIVE MATRIX. Hoo-Kyun Choi*1, Hye-Chin Pak1, Young-Joo Cho1, Sang-Chul Shin2 and Jin-Hwan Lee1. 1College of Pharmacy, Chosun University, Kwangju, Korea; 2College of Pharmacy, Chonnam National University, Kwangju, Korea.

 

Purpose.

To examine the crystallization of ketoprofen in pressure sensitive adhesive matrix and the inhibitory effect of various compounds on the crystallization of ketoprofen.

Methods.

The pressure sensitive adhesive matrix containing ketoprofen was prepared by solvent casting method. Polyisobutylene (PIB) was used as a pressure sensitive adhesive matrix. The drug and appropriate additives were dissolved in PIB solution and the solution was casted on silicone coated release liner using a casting knife. The samples were stored at 25 C. They were examined visually and microscopically at specified time intervals.

Results.

Among various compounds tested, polyvinylpyrrolidone (PVP) was found to be the most effective crystallization inhibitor. The samples containing more than 1.05 % of PVP exhibited no crystallization up to 3 weeks after the storage at 25 C. In the samples containing 1.05 % of Poloxamer 407, tween 20, tween 80, Labrasol, Labrafil 2609, span 80, or Transcutol and in the samples with no additive, ketoprofen crystallized within 1 day after the preparation. In case of span 80, Labrafil 2609, and Transcutol, increasing the amount of each compound up to 3.15% did not change the time for the ketoprofen to start crystallization. However, the samples containing 3.15 % Poloxamer, tween 20, tween 80, or Labrasol showed slower crystal formation compared to those containing less than 3.15 %. When the effect of storage temperature on the crystal formation of ketoprofen was studied using the samples containing 1.05 % PVP, no drug crystallization was observed up to 2 weeks after the storage at 4, 25, 30, 50 and 80 C.

Conclusions.

Ketoprofen was crystallized in PIB pressure sensitive adhesive matrix shortly after the

preparation. The extent of crystallization depended on the amount and the kind of

additives used. Among tested additives, PVP was found to be the most effective

crystallization inhibitor.

http://www.aapsj.org/abstracts/AM_1998/1256.html

We claim:

1. A process for accelerating the absorption of ketoprofen in vivo which comprises

combining 1 part by weight of ketoprofen with 1 to 25 parts by weight of an inorganic

buffer substanceof magnesium hydroxide, magnesium oxide or magnesium carbonate

into a buffered administration form and orally administrating the so combined ketoprofen

and buffer.

2. A process according to claim 1, wherein the active compound is ketoprofen in the form

of its enantiomers S(+)- or R(-)- ketoprofen in pure form or as mixtures in a ratio of 1:99

to 99:1.

3. A process according to claim 1, wherein the buffer substance is at least one of

magnesium oxide and magnesium hydroxide.

4. A process according to claim 1, wherein the buffer substance is magnesium oxide.

5. A Process according to claim 1, wherein said combination is in the form of tablets,

capsules, granules, powder mixtures or suspensions.

6. A process for accelerating the absorption of ketoprofen in vivo which comprises

combining ketoprofen with magnesium hydroxide in a buffered administration form and

orally administrating the so combined ketoprofen and magnesium hydroxide.

7. A process according to claim 6, wherein the active compound is ketoprofen in the form

of its enantiomers S(+)- or R(-)- ketoprofen in pure form or as mixtures in a ratio of 1:99

to 99:1.

8. A process according to claim 6, wherein said combination is in the form of tablets,

capsules, granules, powder mixtures or suspensions. Description: BACKGROUND OF

THE INVENTION

The invention relates to the combined use of ketoprofen and special inorganic basic

substances with an improved quality of action.

It is already known that basic substances such as magnesium hydroxide, magnesium

oxide and sodium bicarbonate or mixtures thereofhave an influence on the absorption of

certain active compounds, such as anthranilic acid derivatives, propionic acidderivatives,

acetic acid derivatives, salicylic acid derivatives or salts thereof or pyrazolols or

benzothiazine derivatives (cf. Neuvonen WO 89/07439). In this Application, ketoprofen

is also mentioned as an example of a propionic acid derivative.

It is also known to the expert that the absorption-regulating effect of certain additives

cannot be generalized for all active compounds (cf. D'Arcy et al., Drug Intelligence and

Clinical Pharmacy, 21, 607 (1987)). The granted claims of theabovementioned PCT

Application by Neuvonen were limited to the specific active compounds tolfenamic acid,

mefenamic acid -and ibuprofen, and only magnesium hydroxide and magnesium oxide

are claimed as basic partners in the combination. This confirms thestatement in the

publication by D'Arcy et al. that the action of basic substances such as antacids on the

absorption properties of active compounds cannot be predicted. The later publication by

Neuvonen in Br. J. Clin. Pharmac. 31, 263 (1991) alsoshows, with the aid of two cross-

over studies, that a higher plasma concentration occurs as a result of addition of

magnesium hydroxide only in the case of ibuprofen. In the case of ketoprofen, neither a

significant increase in the rate of absorptionnor an increased extent of absorption was

found.

SUMMARY OF INVENTION

Knowing of this prior art, it was not to be expected that by combining ketoprofen in

racemic form and in the form of its S(+) and R(-) enantiomers with basic auxiliaries such

as magnesium hydroxide and magnesium carbonate, a faster action and asignificant

increase in the maximum plasma level is achieved as compared with unbuffered tablets.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show the plasma concentration of R(-)- and S(+)- ketoprofens respectively

following administration of buffered verses unbuffered ketoprofen tablets.

FIG. 3 shows the rate of ketoprofen release over time of buffered verses unbuffered

ketoprofen tablets.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1 and FIG. 2, a significant increase in maximum plasma level and a

faster action is achieved using the buffered ketoprofen tablets of the invention versus the

unbuffered tablets.

The absorption-accelerating action of magnesium hydroxide and magnesium carbonate

can be seen from the C.sub.max AUC ratio according to Table 1.

Furthermore, the region of the t.sub.max values starts earlier in the case of the buffered

tablets of the combination according to the invention, and shows less scatter than in the

case of the unbuffered tablets. The comparative studies alsoshow that the interindividual

variation in the individual plasma levels is smaller in the case of the buffered

combination tablets according to the invention than in the case of the unbuffered tablets.

The differences found in the maximum plasma concentrations (C.sub.max) of the three

different tablet formulations are significant. The ketoprofen tablet buffered with

magnesium hydroxide in particular leads to higher plasma concentrations of

theketoprofen being achieved earlier than with the unbuffered tablet. In pain indication in

particular, it is therefore advisable to use the buffered tablets with their faster onset of

action compared with the unbuffered tablets.

The inventive step not only lies in overcoming the prejudice known from the literature

that the absorption of ketoprofen cannot be influenced positively by basic substances, but

is also intensified by our own in vitro test. A study of therelease from ketoprofen tablets

(25 mg) in vitro shows that the formulation with the combination of ketoprofen and

magnesium hydroxide has the slowest release, as can be seen from FIG. 3. From these

negative in vitro results, it was not to be expectedthat the combination of ketoprofen +

magnesium hydroxide in particular shows such advantageous absorption properties in

vivo.

Fixed combinations according to the invention which are of particular interest are those

in the form of tablets, effervescent tablets, capsules, granules, powder mixtures,

suspensions, emulsions and drops, which preferably comprise 1 part byweight of

ketoprofen racemate or S(+)- ketoprofen or R(-)- ketoprofen in pure form or as mixtures

in a weight ratio of 1 to 99 to 99 to 1, and comprise 1 to 25 parts by weight of the basic

buffering additive, in particular magnesium hydroxide.

The buffer capacity of the basic partner of the combination in the presentation forms

according to the invention is preferably at least 3 milliequivalents (meq).

Oral administration forms having a low individual scatter of the plasma concentrations,

an increased rate of absorption and a higher maximum plasma concentration are

preferred.

The fixed combinations according to the invention are prepared by customary methods,

for example by mixing and subsequent pressing or by dissolving the individual

components.

EMBODIMENT EXAMPLES

Example 1

The substances of Example 1 are processed to a tablet which releases ketoprofen at a

moderate rate in vitro.

______________________________________ Non-lacquered tablet Ketoprofen

(racemate) 25.0 mg Magnesium hydroxide 150.4 mg Colloidal silicic acid 12.0 mg

Sodium carboxymethyl-starch 7.0 mg Sodium citrate, tertiary 50.0 mg Magnesium

stearate0.6 mg Coating shell HPM cellulose 1.2 mg Polyethylene glycol 4000 0.4 mg

Titanium dioxide 0.4 mg Total weight 147.0 mg

______________________________________

Peparation

The ketoprofen, magnesium hydroxide, sodium carboxymethyl-starch and sodium citrate

are granulated under aqueous conditions and then dried.

The remainder of the constituents (colloidal silicic acid, magnesium stearate) are admixed

to these granules and this mixture is pressed to tablets of 8 mm diameter on suitable tablet

presses.

Example 1a and 1b

Tablets comprising S(+)- and R(-)- ketoprofen are prepared in an analogous manner.

Example 2

The substances of Example 2 are processed to a tablet which releases ketoprofen rapidly

in vitro.

______________________________________ Non-coated tablet Ketoprofen (racemate)

25.0 mg Magnesium carbonate, basic 258.0 mg Sodium carboxymethyl-starch 10.0 mg

Polyvinylpyrrolidone 25 7.4 mg Colloidal silicic acid 2.0 mg Magnesium stearate0.6 mg

Coating shell HPM cellulose 1.8 mg Polyethylene glycol 4000 0.6 mg Titanium dioxide

0.6 mg Total weight 306.0 mg ______________________________________

Preparation

The ketoprofen, magnesium carbonate, sodium carboxymethyl-starch and PVP are

granulated under aqueous conditions and then dried.

The remainder of the constituents (colloidal silicic acid, magnesium stearate) are added to

these granules and this mixture is pressed to tablets of 9 mm diameter on suitable tablet

presses.

Comparison Example 3(without buffer)

The substances of Example 3 are processed to a tablet which releases ketoprofen rapidly

in vitro. The tablet comprises no buffering additive.

______________________________________ Ketoprofen (racemate) 25.0 mg Maize

starch 48.0 mg Avicel 30.0 mg Lactose 32.0 mg Sodium carboxymethylcellulose (Ac-Di-

Sol) 4.3 mg Magnesium stearate 0.7 mg Coating shell HPM cellulose 0.6 mg

Polyethylene glycol 4000 0.2 mg Titanium dioxide 0.2 mg Total weight 141.0 mg

______________________________________

Preparation

The ketoprofen, maize starch, Avicel, lactose and Ac-Di-Sol are granulated under

aqueous conditions and then dried.

These granules are mixed with magnesium stearate and pressed to tablets of 7 mm

diameter on suitable tablet presses.

TABLE 1

________________________________________________________________________

__ Unbuffered tablet Buffered tablet (Mg(OH).sub.2) Buffered tablet (MgCO.sub.3)

R(-)- S(+)- R(-)- S(+)- R(-)- Parameter ketoprofen ketoprofen ketoprofen ketoprofen

ketoprofen S(+)-ketoprofen

________________________________________________________________________

__ C.sub.max /AUC (1 h) 0.60 0.61 0.84 0.87 0.74 0.75

________________________________________________________________________

__

http://www.patentgenius.com/patent/5776505.html

RESEARCH PAPER Year : 2006  |  Volume : 68  |  Issue : 1  |  Page : 76-82 Design and evaluation of controlled onset extended release multiparticulate systems for chronotherapeutic delivery of ketoprofen

HN Shivakumar1, Sarasija Suresh2, BG Desai1

1 Department of Pharmaceutical Technology, K. L. E. S's College of Pharmacy, Rajajinagar 2nd Block, Bangalore-560 010, India2 Department of Pharmaceutics, Al-Ameen College of Pharmacy, Hosur Road, Bangalore-560 027, India

Correspondence Address:H N ShivakumarDepartment of Pharmaceutical Technology, K. L. E. S's College of Pharmacy, Rajajinagar 2nd Block, Bangalore-560 010 India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0250-474X.22969

    Abstract  

An oral controlled onset extended release dosage form intended to approximate the chronobiology of rheumatoid arthritis is proposed for site-specific release to the colon. The multiparticulate system consisting of drug-loaded cellulose acetate cores encapsulated within Eudragit S-100 microcapsules was designed for chronotherapeutic delivery of ketoprofen. Drug-loaded cellulose acetate cores were prepared by emulsion solvent evaporation technique in an oily phase at different drug:polymer ratios (1:1, 2:1 and 4:1). These cores were successfully microencapsulated with Eudragit S-100 following the same technique at the core:coat ratio of 1:5. Scanning electron microscopy (SEM) revealed that the cellulose acetate cores were discrete, uniform and spherical with a porous and rough surface, whereas the Eudragit microcapsules were discrete and spherical with a smooth and dense surface. In vitro drug release studies of the Eudragit microcapsules were performed in different pH conditions following pH-progression method for a period of 16 h. The release studies indicated that the microcapsules posses both pH-sensitive and controlled-release properties, showing limited drug release below pH 7.0 (6.40 to 8.94%), following which the cellulose acetate cores effectively controlled the drug release for a period of 11 h in pH 7.5. The differential scanning calorimetric and powder X-ray diffraction studies demonstrated that ketoprofen was present in dissolved state in the cellulose acetate polymeric matrix, which could explain the controlled drug release from the cores. The release of ketoprofen from Eudragit microcapsules in pH 7.5

depended on the cellulose acetate levels and was characterized by Higuchi's diffusion model.

How to cite this article:Shivakumar HN, Suresh S, Desai BG. Design and evaluation of controlled onset extended release multiparticulate systems for chronotherapeutic delivery of ketoprofen. Indian J Pharm Sci 2006;68:76-82

How to cite this URL:Shivakumar HN, Suresh S, Desai BG. Design and evaluation of controlled onset extended release multiparticulate systems for chronotherapeutic delivery of ketoprofen. Indian J Pharm Sci [serial online] 2006 [cited 2010 Jan 27];68:76-82. Available from: http://www.ijpsonline.com/text.asp?2006/68/1/76/22969

Chronotherapeutics refers to a clinical practice of synchronizing drug delivery in a manner consistent with the body's circadian rhythm, including disease states, to produce maximum health benefit and minimum harm[1]. The site-specific delivery of drugs to the colon has implications in a number of therapeutic areas, which include topical treatment of colonic disorders such as Crohn's disease, ulcerative colitis, constipation, colorectal cancer, spastic colon and irritable bowel syndrome. A colonic delivery system would additionally be valuable when a delay in absorption is therapeutically desirable in treatment of diseases like rheumatoid arthritis, which are influenced by circadian rhythms[2]. The disease is known to have the peak symptoms when awaking from nighttime sleep.

Ketoprofen is a potent non-steroidal anti-inflammatory drug with a short biological which is prescribed for long-term treatment of musculoskeletal and joint disorders such as rheumatoid arthritis, osteoarthritis, alkylosing spondilytis and acute gout[3]. The mechanism of action of ketoprofen is mainly associated to the inhibition of the body's ability to synthesize prostaglandin. Adverse effects on the gastric mucosa have been observed when the drug is administered orally. Ketoprofen is rapidly absorbed from the gastrointestinal tract and reaches high bioavailability (>92%). The drug has been reported to be transported across the intestinal epithelial cells by trans-cellular passive diffusion[4].

Colon-specific delivery can be achieved with a suitable mechanism that triggers off the drug release upon reaching the colon. The physiological change in the pH of the gastrointestinal tract has been extensively exploited to convey the actives to the colon. Methods based on pH-sensitive delivery, such as delayed-onset dosage forms, could be a simple and practical means for colon targeting. Several polymers, particularly Eudragit S-100[5] and EudragitTMS[6], have been investigated for colonic delivery. These polymers have been designed to be soluble at pH values higher than 7, keeping in mind the pH prevalent in the large intestine. As reported, the pH of the colon in normal subjects drops

from 7.5±0.4 in the terminal ileum to 6.4±0.6 in the ascending colon[7]. However, the major disadvantage of these systems is the possibility of the drug being released in the terminal ileum rather than the colon. This problem was thought to be solved by utilizing two polymers: one having pH-sensitive, and the other imparting a controlled-release property. Eudragit S was used to prevent the drug release till the formulation reaches the terminal ileum, whereas cellulose acetate avoids the complete release in the ileum and effectively conveys the drug to the colon.

A multiparticulate system presents several advantages in comparison to single unit forms in that they exhibit higher colonic residence time, more predictable gastric emptying, and cause less local irritation[8]. With all these considerations in mind, a multiparticulate system consisting of drug-loaded cellulose acetate cores encapsulated within Eudragit S-100 microcapsules was designed for chronotherapeutic delivery of ketoprofen. As a core forming polymer, cellulose acetate, whose application in the microencapsulation has been extensively investigated, was selected[9]. With this system, the aim was to minimize drug release in the upper part of the gastrointestinal tract and target the drug to the colon.

    Materials and methods  

Ketoprofen was kindly donated by Rhone Poulenc (I) Ltd., Mumbai. Eudragit S-100 was generously donated by Rohm Pharma, Darmstadt, Germany. Cellulose acetate was supplied by Rolex Chemicals, Mumbai. The rest of the chemicals of analytical grade, supplied by S. D. Fine Chemicals, Mumbai, included light liquid paraffin, Span-80, acetone, n-hexane, and methanol.

Preparation of cellulose acetate cores containing ketoprofen:

Cellulose acetate cores containing ketoprofen were prepared by emulsion-solvent evaporation technique in an oily phase[10]. Cellulose acetate was dissolved in acetone to get a homogenous polymer solution (1% w/v). Ketoprofen was dissolved in 10 ml of the polymer solution at drug:polymer ratio of 1:1, 2:1 and 4:1, and the resulting solution was added in thin streams to 70 ml of liquid paraffin containing 1% w/w of span-80. About 10 ml of acetone was added to the external phase to produce a stable o/o emulsion. The system was maintained under constant stirring (1000 rpm) using a variable speed propeller stirrer (RQ 125 D, Remi Udyog Ltd., Mumbai) for a period of 3 h to allow complete solvent evaporation. The cellulose acetate cores formed were separated, washed with n-hexane, and dried for 48 h in a vacuum desiccator.

Microencapsulation of drug-loaded cellulose acetate core:

Cellulose acetate cores containing ketoprofen were encapsulated following the same technique with Eudragit S-100[10]. The drug-loaded cellulose acetate cores (100 mg) were suspended in 5 ml of ethanolic solution of Eudragit S-100 (10% w/v) and emulsified into 70 ml of liquid paraffin containing 1% w/w of span-80. Emulsification was

maintained using a variable-speed propeller stirrer at 1000 rpm to allow complete solvent evaporation. The microcapsules formed were separated, washed with n-hexane, and dried for 48 h in a vacuum desiccator.

IR spectra of ketoprofen, cellulose acetate, Eudragit S and the microcapsules were recorded in a FTIR spectrophotometer (Jasco FTIR, 460 plus) to check the chemical integrity of the drug in the microcapsules[11].

Scanning electron microscopy (SEM):

Morphology and surface topography of the microparticles were examined by scanning electron microscopy[12] (SEM-Jeol, JSM-840A, Japan). The samples were mounted on the SEM sample stab, using a double-sided sticking tape and coated with gold (200A°) under reduced pressure (0.001 torr) for 5 min to improve the conductivity using an Ion sputtering device (Jeol, JFC-1100 E, Japan). The coated samples were observed under the SEM and photomicrographs of suitable magnifications obtained.

Particle-size distribution:

The particle-size distribution of the microparticles was determined using optical microscopy[12]. The projected diameter of a total of 200 microparticles from each batch was observed. The size distribution data got were attempted to fit into normal and log normal distribution, and the equivalent diameter based on surface number basis (dsn) was computed using Hatch-choate equation[13].

Estimation of drug content:

An accurately weighed quantity of the microparticles was dissolved in acetone. The acetone was evaporated and the residue left behind was vortexed with 75% methanol for 30 min to extract the drug. The dispersion was filtered and the absorbance of the filtrate was measured at 258 nm after appropriate dilution in a UV-visible spectrophotometer (Jasco V-530, Japan). The drug content was estimated in triplicate using a calibration curve constructed in the same solvent. Polymers did not interfere with the assay at this wavelength.

Thermal analysis[11]:

Samples of the ketoprofen, cellulose acetate, physical mixtures and the cellulose acetate cores were taken in a flat-bottomed aluminium pans and heated over a temperature range of 40-180° at a constant rate of 5°/min with purging of nitrogen (50ml/min) using alumina as a reference standard in a differential scanning calorimeter (Perkin Elmer DSC, Pyris-1).

X-ray powder diffraction studies[11]:

The diffraction studies were carried out in a powder X-Ray diffractometer (Philips, PW

1050/37) with a vertical goniometer using Cu K a radiation with Ni filter at a voltage of 40 kV and a current of 20 mA. Powder XRD patterns for ketoprofen, cellulose acetate, physical mixture and cellulose acetate cores were obtained by scanning from 0 to 50° 2q.

In vitro drug release studies:

Dissolution studies of the Eudragit microcapsules were carried out in triplicate employing USP XIII dissolution rate test apparatus-1 (Electrolab, TDT-06T) following pH progression method simulating the gastrointestinal tract conditions[10]. Weighed quantities of the microcapsules were loaded into the basket of the dissolution apparatus, and the pH changes were performed, starting with 900 ml of 0.1 N hydrochloric acid for 2 h, mixed phosphate buffer of pH 5.5 for 1 h, phosphate buffer of pH 6.8 for 2 h, followed by mixed phosphate buffer of pH 7.5 till the end of the test. The temperature of the dissolution fluid was maintained at 37±0.5° with a stirring speed of 100 rpm. The samples were withdrawn every hour, filtered through a Millipore filter (0.22 mm), and assayed spectrophotometrically at 258 nm for the samples of pH 1.2, and at 260 nm for the rest of the samples. However, the dissolution studies of the cellulose acetate cores were also performed under the same set of experimental conditions using mixed phosphate buffer of pH 7.5 as the dissolution fluid mimicking the pH at the end of the small intestine[7].

    Results and discussion  

The compositions of different batches of cellulose acetate cores are shown in [Table - 1].

Cellulose acetate cores containing ketoprofen were prepared by emulsion solvent

evaporation technique, where the organic solution containing the drug and cellulose

acetate in acetone was emulsified into an external oil phase of liquid paraffin. A small

amount of acetone added to the external oily phase was known to avoid rapid diffusion of

the organic solvent into the oily phase. This would prevent immediate polymer

precipitation before the organic solution could be dispersed into droplets in the oily phase

leading to formation of a stable emulsion. Span 80 (1% w/w) was used as an emulsifier to

stabilize the o/o emulsion produced.

Photomicrographs of the cellulose acetate cores are shown in [Figure - 1]a. It is vivid

from SEM photomicrographs that the cores were discrete, uniform and spherical with a

porous and rough surface. The rough surface of the cores can be attributed to the rapid

solvent diffusion and quick precipitation of cellulose acetate during the formation of o/o

emulsion. It has been reported that microspheres with a porous and rough surface were

produced by solvent evaporation technique with crystalline polymers[14].

The viscosity of the polymer solution used during microencapsulation is known to

determine the size of the microspheres produced[10]. The viscosity of the organic

solution depended on the polymer concentration in the solution, organic solvent used and

the temperature. Since all the three batches of cellulose acetate cores were prepared using

the organic solution having the same polymer concentration (1% w/v of cellulose

acetate), there was no significant difference in the emulsion globule size. Accordingly,

the cellulose acetate cores of the three batches did not vary significantly in their size. The

size distribution data obtained from optical microscopy, when represented as log-

probability plots, gave straight lines indicating a log-normal distribution in all the three

batches of cellulose acetate cores produced. The surface number diameters (dsn) of the

three batches of drug-loaded cores, as computed using Hatch-choate equation, are

represented in [Table - 1].

The percent drug loading and entrapment efficiency of the three batches of drug loaded

cores are depicted in [Table - 1]. The values of entrapment efficiency were found to

decrease with increase in the initial drug loading, which can be ascribed to better drug

entrapment within the cores with increase in cellulose acetate levels. The drug loss during

the microencapsulation process can possibly be related to the partitioning of the drug to

the oil phase.

The in vitro release profiles of cellulose acetate cores are portrayed in [Figure - 2]. As the

cellulose acetate cores remain protected by the Eudragit S-100 coat below pH 7, the

dissolution tests of the cellulose acetate cores were conducted using phosphate buffer of

pH 7.5 also mimicking the pH prevalent at the end of the small intestine[7]. The

dissolution studies indicated that the cores were characterized by an initial burst effect

during the first hour. The burst effect was reduced with increasing cellulose acetate levels

in the cores, which may be attributed to better drug entrapment within the cores with

increase in cellulose acetate levels. The slow release phase was followed by a controlled

release phase, during which the drug release depended on the cellulose acetate levels in

the cores. The mechanism of drug release was found to be characterized by Higuchi's

diffusion model[15] as plots of amount of drug released versus square root of time were

found to be linear. The values of Higuchi rate constant (KH) were found to range

between 16.1 to 23.3 %h -1/2 with a distinct increasing trend as the cellulose acetate levels

in the cores decreased. The effect of varying cellulose acetate levels in matrix diffusional

systems on drug release has been documented[9].

DSC has been one of the most widely used calorimetric techniques to characterize the

solubility and physical state of drug in the polymeric matrix. [Figure - 3] depicts the DSC

thermograms of ketoprofen, cellulose acetate, physical mixtures and cellulose acetate

cores. The DSC thermogram of ketoprofen exhibited a single sharp endothermic peak at

94.34° corresponding to its melting transition temperature[16]. This peak was also

observed in the thermogram of the physical mixture, even though slightly broadened but

shifted to lower temperature (94.06°). This may be possibly due to fact that presence of

cellulose acetate in the physical mixture depresses the melting point of ketoprofen and

broadens its melting point endotherm. The thermograms of the drug-loaded cellulose

acetate cores showed no such characteristic peak, indicating that the drug was present in

the dissolved state in cellulose acetate polymer matrix.

Powder XRD technique has been extensively utilized along with DSC to study the

physical state of drug in the polymer matrix. Powder XRD patterns for ketoprofen,

cellulose acetate, physical mixture and cellulose acetate cores are shown in [Figure - 4].

The crystalline nature of ketoprofen was clearly demonstrated by its characteristic PXRD

pattern containing well-defined peaks. The PXRD diffractogram of the physical mixture

of the drug and cellulose acetate also exhibited the characteristic diffraction pattern of the

crystalline drug, indicating that the drug was dispersed in cellulose acetate in the physical

mixture, The PXRD spectra of the cores did not reveal any such characteristic PXRD

pattern corresponding to the crystalline drug, confirming the fact that the drug existed in

the dissolved state in the cellulose acetate polymer matrix. These results could explain the

controlled drug release from the cellulose acetate cores.

The second part of the research work was focused on microencapsulation of the cellulose

acetate cores with a pH-sensitive acrylic polymer. The drug-loaded cores were

microencapsulated following the emulsion solvent evaporation technique with Eudragit

S-100 that dissolves at pH of above 7. Eudragit S was selected to protect the cellulose

acetate cores in the upper part of the gastrointestinal tract, avoiding any significant drug

release before reaching the colon. Once the acrylic coat dissolves, it was expected that the

cellulose acetate cores would effectively control the drug release at the target site.

As a part of the research work, a preliminary screening study was undertaken to select a

suitable organic solvent that would dissolve Eudragit S-100 and, at the same time,

maintain the integrity of the cellulose acetate cores. Ethanol was chosen as solvent as it

met the above said criteria; moreover, ethanol diffuses quickly into the external oily

phase, resulting in encapsulation of the drug-loaded cellulose acetate cores. [Table - 2]

depicts the compositions of different batches of Eudragit microcapsules.

SEM revealed that the Eudragit microcapsules were discrete, uniform and spherical, with

a smooth and dense surface. The photomicrographs of the Eudragit microcapsules are

portrayed in [Figure - 1]b. It has been already established that microspheres with a

smooth and dense surface were produced by solvent evaporation technique with

amorphous polymers[14].

As mentioned earlier, the particle size of the microcapsules produced depended on the

viscosity of the polymer solution used. As all the three batches of microcapsules were

produced using the polymer solution having the same Eudragit concentration (10% w/v),

the microcapsules of the three batches did not differ significantly in their particle size.

The particle size distribution data, as determined by optical microscopy when represented

as log-probability plots, gave straight lines indicating a log-normal distribution in all the

three batches of microcapsules produced. The surface number diameters (dsn) of the

three batches of microcapsules, along with their percentage drug loading and

encapsulation efficiency values, are represented in [Table - 2]. The values of percentage

drug loading and encapsulation efficiency portray that emulsion solvent evaporation

technique allows favourable drug encapsulation using Eudragit S 100.

IR Spectrophotometry has been employed as a useful tool to identify the drug excipient

interaction. The IR spectra of ketoprofen and the microcapsules were identical. The

principal IR absorption peaks of ketoprofen at 1698 cm-1 (carboxylic acid carbonyl) and

1655 cm-1 (ketonic carbonyl) appeared in the spectra of ketoprofen as well as the

microcapsules. These observations indicated no chemical interaction between the drug

and other excipients used.

[Figure - 5] portrays the in vitro drug release profiles of Eudragit microcapsules as

determined by pH progression method. The studies showed that the microcapsules

exhibited both pH-sensitive and controlled-release properties. The drug release depended

on the pH of the dissolution media and the cellulose acetate levels in the microcapsules.

A limited drug release was observed from the microcapsules below pH 7 during the first

five hours of dissolution (6.39 to 8.94 %), which can be ascribed to the pH-sensitive

nature of Eudragit S-100 coating. Eudragit S-100 is a pH-sensitive acrylic polymer

having a threshold pH of 7 5. It was observed that once the acrylic coating dissolved at pH

7.5, the cellulose acetate cores effectively controlled the drug release for a period of 11 h.

As revealed by the DSC and PXRD studies, the physical state of ketoprofen in the

cellulose acetate polymeric matrix could explain the controlled release of the drug from

the cellulose acetate cores. Diffusion of the drug through the cellulose acetate polymeric

matrix was the rate-controlling step that could characterize the mechanism of drug

release. The mechanism of drug release from the microcapsules in pH 7.5 was found to

be diffusion controlled and was characterized by Higuchi's diffusion model. The values

of kinetic constant ranged between 15.79 to 22.31% h -1/2, showing a distinct increasing

trend as the cellulose acetate levels in the Eudragit microcapsules decreased.

A multiparticulate system having both pH-sensitive and controlled-release property is

described for chronotherapeutic delivery of ketoprofen. The results collectively prove

that dual coated microcapsules with enteric and controlled release properties can be

successfully developed using double microencapsulation procedure. Bedtime

administration of such a device could improve the anti-inflammatory therapy in the

management of rheumatoid arthritis.

http://www.ijpsonline.com/article.asp?issn=0250-

474X;year=2006;volume=68;issue=1;spage=76;epage=82;aulast=Shivakumar

Indian journal of pharmaceutical sciences

Nanoparticles Containing Ketoprofen and Acrylic Polymers Prepared by an Aerosol Flow Reactor MethodHannele Eerikäinen,1,2  Leena Peltonen,3  Janne Raula,1  Jouni Hirvonen,3  and Esko I. Kauppinen1,4 

1Center for New Materials, Helsinki University of Technology, PO Box 1602, FIN-02044 VTT, Finland2Present address: Orion Corporation Orion Pharma, Pharmaceutical Product Development, PO Box 65, FIN-02101 Espoo, Finland3Faculty of Pharmacy and Viikki Drug Discovery Center, University of Helsinki, PO Box 56, FIN-00014 Helsinki, Finland4Aerosol Technology Group, VTT Processes, PO Box 1602, FIN-02044 VTT, Finland

Correspondence to:Esko I. KauppinenTel: +358 9 456 6164Fax: +358 9 456 7021Email: Esko.Kauppinen@vtt.fi

Submitted: April 27, 2004; Accepted: September 23, 2004; Published: December 31, 2004

Keywords:  nanoparticles, ketoprofen, aerosol, polymer, Eudragit

Abstract

The purpose of this study was to outline the effects of interactions between a model drug and various acrylic polymers on the physical properties of nanoparticles prepared by an aerosol flow reactor method. The amount of model drug, ketoprofen, in the nanoparticles was varied, and the nanoparticles were analyzed for particle size distribution, particle morphology, thermal properties, IR spectroscopy, and drug release. The nanoparticles produced were spherical, amorphous, and had a matrix-type structure. Ketoprofen crystallization was observed when the amount of drug in Eudragit L nanoparticles was more than 33% (wt/wt). For Eudragit E and Eudragit RS nanoparticles, the drug acted as an effective plasticizer resulting in lowering of the glass transition of the polymer. Two factors affected the preparation of nanoparticles by the aerosol flow reactor method, namely, the solubility of the drug in the polymer matrix and the thermal properties of the resulting drug-polymer matrix.

Introduction

Drug nanoparticles can be defined as drug-containing particles having size smaller than 1 µm.1,2 These submicron-sized particles consist of the drug and, optionally, a stabilizing or

functional biocompatible polymer. Several applications of nanoparticles have been proposed, such as tissue targeting in cancer therapy,3 controlled release,4 carrier action for the delivery of peptides,5,6 and increase in the solubility of drug.7

Previously, a method capable of producing drug-polymer nanoparticles, namely, an aerosol flow reactor method, has been presented.8,9 This method produces spherical, amorphous, matrix-type drug-polymer nanospheres directly as dry powder in a 1-step operation. In the previous study,9 the properties of nanoparticles consisting of an acrylic polymer, Eudragit L, and drug materials ketoprofen or naproxen were studied. It was observed that crystallization of the drug in the polymer matrix was the limiting factor for drug loading. In this study, the polymeric component is varied, while ketoprofen is used as a model drug.

The polymer nanoparticles prepared by the aerosol flow reactor method have an amorphous solid solution structure.9 When the polymer glass transition temperature is above the ambient temperature, the polymeric component is in a glassy state, which provides mechanical strength to the particles. Therefore, the mechanical hardness and integrity of the particles can be maintained and coalescence of the particles can be avoided, which allows the collection as dry powder.

The aim of this study was to evaluate how different polymers and interactions between the drug and the various polymers affect the physical state of the nanoparticles. Three acrylic polymers were used in this study. These functional polymers, namely, Eudragit L, Eudragit RS, and Eudragit E, are widely used in the pharmaceutical industry, and are accepted for oral use.10 These 3 polymers have different chemical compositions and functional groups. For the purposes of this study, first, it was expected that the solubility properties of the nanoparticles could be varied due to different solubilities of the polymers.10,11 Second, as the functional groups of the polymers are different, interactions between the polymers and the acidic model drug molecule, ketoprofen, were expected to be different.

The structural formulas of the polymer materials used are shown in Figure 1. Eudragit L is a copolymer consisting of methyl methacrylate and methyl methacrylic acid repeating units in a ratio of 1:1.10 It is soluble when the pH is greater than 6 due to the ionization of the acid groups; below this pH it is insoluble.11 Eudragit E is a copolymer consisting of a 1:2:1 ratio of methyl methacrylate, dimethylaminoethyl methacrylate, and butyl methacrylate monomers.10 The tertiary amino groups are ionized at acidic conditions, and this polymer is soluble when the pH less than 5.11 Eudragit RS is a copolymer consisting of ethyl acrylate, methyl methacrylate, and trimethylammonioethyl methacrylate chloride in a ratio of 1:2:0.1.10 This polymer has pH-independent permeability.11

Materials and Methods

Preparation of Particles

Materials

Ketoprofen (2-(3-Benzoylphenyl) propionic acid) was purchased from Sigma (St Louis, MO) and was used as received. Eudragit L 100 PO, Eudragit RS 100 PO, and Eudragit E 100 were obtained from Röhm (Röhm Pharma, Darmstadt, Germany), and were used as received.

Preparation of Drug Solution

The drug-polymer solutions were prepared by separately dissolving the polymer and drug into ethanol (99.6%, Alko Oyj, Rajamäki, Finland) using a magnetic stirrer and combining the solutions at respective amounts. Total solids concentration of the starting solution was fixed at 2 g/L. The compositions of prepared particles are shown in Table 1.

Experimental System Set-up

The experimental system set-up for the preparation of nanoparticles has been described in detail previously.8,9 Briefly, the ethanolic solution containing the drug and the polymer was atomized using a collision-type air jet atomizer TSI 3076 as the aerosol generator (TSI Inc Particle Instruments, St Paul, MN). The resulting droplets were suspended into nitrogen, and the aerosol generated was passed through a heated tubular laminar flow reactor, which was used to evaporate the solvent from the droplets and to allow particle formation to complete. The reactor wall temperature used in this study was kept constant at 80°C and the flow rate of carrier gas was 1.5 L/min. The nanoparticle aerosol was diluted in a porous tube aerosol diluter with nitrogen (20°C) in a ratio of 1:17 before collecting the nanoparticles with a Berner-type low-pressure impactor onto aluminum foil.

Powder Collection

Dry powder samples of particles were collected after diluting the aerosol (ratio 1:17, dilution gas nitrogen at 20°C) using a Berner-type low-pressure impactor onto aluminum foil. The impactor was kept at room temperature. The impactor classified the aerosol into 11 stages, and for this study, the dry powder samples were formed by combining the material deposited on stages 1 to 9. The dry powder samples were stored in a refrigerator (+2 to +8°C) prior to analyses. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations, differential scanning calorimetry (DSC) analyses, infrared spectroscopy (IR) analyses, and drug release analyses were performed for these dry powder samples.

Characterization of Particles

Particle Morphology

Particle morphology was analyzed using a field-emission SEM (Leo DSM982 Gemini, LEO Electron Microscopy Inc, Oberkochen, Germany) using an acceleration voltage of 2 kV. The samples from dry powder particles were prepared by gently dipping a copper grid (for SEM) or lacey carbon-coated copper grid (for TEM) (Agar Scientific Ltd, Essex, UK) into the dry nanoparticles and carefully blowing off excess material. The samples for SEM observations were coated with a thin platinum coating. Particle morphology and internal structure were further analyzed using a field-emission TEM (Philips CM200 FEG, FEI Co, Eindhoven, the Netherlands) using an acceleration voltage of 200 kV.

Particle Size and Size Distribution

Particle size distribution analysis was performed directly from the nanoparticle aerosol using a TSI scanning mobility particle sizer (SMPS), equipped with a long differential mobility analyzer (DMA, model 3081; TSI Inc Particle Instruments) and a condensation particle counter (CPC, model 3022; TSI Inc Particle Instruments). For particle size measurements, an additional aerosol diluter (1:10, dilution gas nitrogen at 20°C) was added before the measurements to reduce the particle concentration to a suitable level. The particle number size distribution measurements were performed 6 times at each experimental condition to reduce random error, and an average of the 6 measurements was calculated and used for analysis.

Differential Scanning Calorimetry

The thermal behavior of the particles was analyzed using a DSC instrument (Mettler Toledo DSC 822e, Mettler Toledo AG, Greifensee, Switzerland) equipped with a Stare computer program. Approximately 3 mg of sample was accurately weighed into a 40-µL aluminum pan and sealed with a punched lid. Temperature range of -50°C to 200°C was scanned using a heating rate of 10°C/min. A nitrogen purge of 50 mL/min was used in the oven. The samples were heated above their Tg and studied using a microscope (Zeiss Axioskop, Oberkochen, Germany) equipped with a heating stage (Linkam THMS 600, Surrey, UK). When the samples were heated above glass transition temperature, Tg, it was observed that the nanoparticles formed a coalesced drug-polymer matrix and did not consist of single, separate nanoparticles anymore. Therefore, to characterize the thermal behavior of the nanoparticles, Tg values were determined in the first heating cycles in DSC experiments.

Infrared Spectroscopy

Infrared absorption spectra of raw materials and nanoparticles in the wavelength region 4000 cm-1 to 650 cm-1 were recorded using a Fourier transform IR spectrometer (Spectrum One, PerkinElmer Instruments LLC, Shelton, Connecticut) equipped with a

Universal ATR sampling accessory (PerkinElmer Instruments LLC, Shelton, Connecticut). Resolution used in the scans was 1 cm-1, and the spectra were averaged over 3 scans.

Drug Release from Nanoparticles

Drug release tests were performed using a system based on the general drug release standard for delayed-release (enteric-coated) articles, method A.12 An amount of nanoparticles corresponding to ~2 mg of ketoprofen was weighed and filled into a size 0 gelatin capsule. The capsule was further girdled with a metal wire to ensure that the capsule settled down in the vessel.13 Round-bottomed cylindrical glass vessels having a total volume of ~150 mL were used as release chambers. The solutions were stirred using a magnetic stirrer at a speed of 50 rpm. The temperature was controlled to 37.0°C ± 0.5°C. In the acid stage, 75 mL of 0.1 N hydrochloric acid was used as the release medium. Aliquots were withdrawn at predetermined time intervals and immediately replaced with fresh medium equilibrated at 37°C. After 2 hours, 25 mL of 0.2 M tribasic sodium phosphate was added to change the pH of the test medium to 6.8, and the test was continued for a further 4 hours. The amount of the drug released was determined using a spectrophotometer (Pharmacia LKB Ultrospec III, Pharmacia LKB Biochrom Ltd, Cambridge, UK) using wavelength of 260 nm. The tests were performed with 2 parallel runs; the values reported are mean values of the 2 runs. The repeatability of the method was evaluated by analyzing 6 parallel samples, and it was found that the results are repeatable. The measured dissolution values have a standard deviation of 6% on average, while the maximum standard deviation was less than 10%. The highest standard deviation values were observed immediately after the pH change, probably due to incomplete mixing and equilibration of the pH in the dissolution vessel.

Results and Discussion

Effect of the Polymer and the Amount of Drug on Particle Size

The atomizer used to spray the nanosized droplets produced a unimodal and lognormal droplet size distribution. After drying the droplets, the particle size distribution of the solid nanoparticles reflected the droplet size distribution produced by the atomizer. The geometric standard deviation of the distributions was less than 2.0 for all the studied drug-polymer particles, which was in good accordance with the atomizer specifications.14 In Figure 2, particle size distributions of nanoparticles containing 10% (wt/wt) ketoprofen are shown. The number mean geometric particle size was calculated from the size distribution curve. In Figure 3, the number mean particle sizes are plotted as a function of drug amount. As a general trend, the particle size slightly decreased as the amount of drug was increased in the nanoparticles. It was observed that Eudragit L produced larger particles than either Eudragit E or Eudragit RS, and that Eudragit RS produced the smallest particles. This was most likely caused by different viscosities and surface tensions of the solutions, which affected the atomization and the droplet size.15

Collection of the Nanoparticles

The different polymers used led to different stability of the nanoparticles during collection. Powders could be collected when the amount of drug was equal to or less than 50% (wt/wt) for Eudragit L nanoparticles, whereas for Eudragit E and Eudragit RS nanoparticles, nanoparticles containing 33% (wt/wt) or less drug could be collected. When higher amounts of drug were incorporated to these polymers, the product collected was tacky and transparent, and seemed not to consist of individual particles.

The collected powders were analyzed by electron microscopy to observe the morphology of the nanoparticles. The nanoparticles made of polymer Eudragit L and containing 33% (wt/wt) or less of drug were spherical, had smooth surfaces, and showed no crystallites (see Figure 4A). When the amount of drug was 50% (wt/wt), some crystallites were also observed. For Eudragit E, the nanoparticles containing 10% (wt/wt) or less drug were spherical, separate nanoparticles. When the drug amount was increased to 25% (wt/wt), the nanoparticles showed coalescence, and separate nanoparticles could not be detected (see Figure 4C). Similarly to Eudragit E, the Eudragit RS nanoparticles were separate, distinct nanoparticles when the amount of drug was 10% (wt/wt) or less (see Figure 4B). Also for these nanoparticles, coalescence and loss of integrity was found when the amount of drug was 25% (wt/wt), as shown in Figure 4D. The compositions and observed appearances of the nanoparticles prepared are summarized in Table 1.

TEM observations were performed for the successfully prepared nanoparticles. Transmission electron microscopy (see Figure 5) showed solid, homogeneous drug-polymer particles. Grain boundaries or crystals were not detected and, therefore, it was concluded that these nanoparticles had a matrix-type structure.

Thermal Behavior of the Nanoparticles

To explain the reason for the coalescence of the nanoparticles, the thermal behavior of the particles was analyzed with DSC. Specifically, the glass transition temperature of the composite nanoparticles was determined. The Tg values are listed in Table 2. For the nanoparticles prepared from Eudragit L, the glass transition was slightly lowered as a function of drug amount (see Table 2). However, the glass transition of all Eudragit L nanoparticles was clearly above room temperature. When the drug amount was equal to or less than 33% (wt/wt), the DSC curves showed no signal attributable to melting peak of the drug (see Figure 6). Therefore, it could be concluded that the drug was incorporated in these nanoparticles in an amorphous form.16-20 For the nanoparticles

containing 50% (wt/wt) drug, however, an endothermic transition attributable to the melting of drug crystals was observed at 94°C. Pure ketoprofen showed a distinct crystal melting peak at 96°C (see Figure 6). For the nanoparticles containing 50% (wt/wt) drug, the solubility limit of drug in the polymer matrix was exceeded, and the excess drug formed crystals. The ketoprofen melting peak appeared at a lower value in the nanoparticles, most likely due to small, imperfect drug crystals formed in the polymer matrix.21 Also, interaction with the polymer could lead to lowering of the melting point.18,21,22

On the contrary, for the nanoparticles prepared from Eudragit RS or Eudragit E, crystallization of drug could not be detected within the composition range studied (see Figure 6). As no crystals were observed, the amount of ketoprofen was below the solubility limit of ketoprofen in these polymer matrices. Instead, a significant lowering in the glass transition temperature of the polymer was observed, as shown in Table 2. The glass transition temperatures of Eudragit E and Eudragit RS composite nanoparticles were much lower than of Eudragit L nanoparticles. For Eudragit E and Eudragit RS nanoparticles, when the drug amount was 25% (wt/wt), the glass transition temperatures were close to room temperature. The glass transition temperatures measured were 24°C and 28°C for the Eudragit E and Eudragit RS nanoparticles, respectively. The glass transition temperatures were close to the collection temperature (room temperature) of the nanoparticles. Consequently, the nanoparticles were softened and the mechanical strength was not sustained. Ketoprofen drug molecule acted as an effective plasticizer for these polymers, lowering the glass transition temperature.23,24

IR Spectroscopy

Infrared spectroscopy was used to study the interactions between the drug and the polymers. Ketoprofen has a carboxylic acid group, which can interact with the functional groups of the polymers. The carbonyl peaks in the IR spectra of ketoprofen were recorded at 1694 cm-1 and 1654 cm-1, and have previously been assigned to dimeric carboxylic acid carbonyl group and ketonic carbonyl group stretching vibrations, respectively.25,26

Exemplary IR spectra of the nanoparticles are shown in Figure 7. For clarity and stronger absorptions arising from ketoprofen, materials containing 33% (wt/wt) ketoprofen are shown as examples, even though nanoparticle collection was not successful for all these. Considering first the nanoparticles containing no drug but only polymer (Figure 7, Eudragit L curve C), the Eudragit L polymer contains both carboxylic acid and ester groups. Therefore, the IR spectra showed overlapping carbonyl vibrations of the ester group at 1724 cm-1 and the carboxylic acid at 1710 cm-1.27 However, when ketoprofen was included in the nanoparticles, this peak was split into 2 peaks as a function of increasing drug amount (see Figure 7, Eudragit L curve B). The peak at ~1724 cm-1 could

be attributed to stretching vibrations of the ester group carbonyl, similarly to Eudragit E and Eudragit RS polymers. However, the peak at the lower wavenumber was recorded at 1710 cm-1, 1705 cm-1, 1703 cm-1, 1700 cm-1, 1700 cm-1, and 1699 cm-1 for the nanoparticles containing 0% (wt/wt), 5% (wt/wt), 10% (wt/wt), 25% (wt/wt), 33% (wt/wt), and 50% (wt/wt) ketoprofen, respectively. This peak was interpreted as arising due to the formation of a dimer by the carboxylic acid groups of the polymer and the drug. Due to the formation of the dimer, the vibration of the carboxylic acid carbonyl was shifted to lower wavenumbers.

From Figure 7 it can be seen that the Eudragit RS and Eudragit E materials exhibit quite similar spectra (Figure 7, Eudragit RS curve C and Eudragit E curve C). The strong stretching vibration of the carbonyl moiety of ester groups could be identified for both the materials at ~1724 cm-1.28 For the Eudragit E and Eudragit RS nanoparticles containing ketoprofen, the position of the ester group carbonyl peak at 1724 cm-1 was not changed (see Figure 7, Eudragit E curve B and Eudragit RS curve B). However, the peak corresponding to the carboxylic acid group of ketoprofen at 1694 cm-1 was not seen in the spectra of the composite nanoparticles, whereas the peak arising from the ketone carbonyl at 1654 cm-1 could be identified. The carboxylic acid group of the ketoprofen molecule interacted with the polymers, leading to the disruption of the carboxylic acid dimer of the crystalline ketoprofen. As a result, the carboxylic acid stretching vibration occurred at higher wavenumbers,25,26 was overlapped by the strong ester vibrations of the polymer, and could not be detected.

Eudragit E is a polymer containing secondary amino groups capable of accepting a proton from an acid molecule. It was initially assumed that at least a fraction of the amino groups of the polymer would be protonated by the acidic drug in the ethanolic solution. The peaks corresponding to the amino groups have been identified previously29 at 2820 cm-1 and 2770 cm-1. However, any change in the position of these peaks was not observed when ketoprofen was incorporated in the nanoparticles. Therefore, it was concluded that ketoprofen drug mainly interacted with the ester groups of the Eudragit E polymer, similarly to Eudragit RS.

Drug Release

Drug release was evaluated for the nanoparticles prepared from different polymers, and the results are shown in Figure 8. Nanoparticles prepared from Eudragit L showed an initial, instant release of ~30% of the drug in the acidic stage of the test. However, the drug release was slightly slower than of pure ketoprofen. After the pH change, complete dissolution of the nanoparticles took place rapidly. At the buffer conditions (pH 6.8), the Eudragit L copolymer was ionized and soluble in the medium, thereby releasing the drug immediately. Eudragit E polymer, however, is soluble at the acidic conditions. Complete release of the drug was obtained for Eudragit E nanoparticles in the acidic medium in less than 15 minutes as a result of polymer dissolution. As the polymer dissolved, also the drug contained in the nanoparticles was forced into the solution. Drug release from the

nanoparticles was much faster than of pure ketoprofen (see Figure 8). Eudragit RS nanoparticles showed sustained release of the drug at the acidic conditions, and the drug release was found to be approximately linear. Similar to Eudragit L nanoparticles, ~30% of the drug was released initially. Further drug release from the nanoparticle matrix was controlled by the polymer. When the pH was changed, the amount of the released drug changed rapidly from ~60% to almost 80%. At the buffer conditions, release of the drug was faster as the ketoprofen molecules were ionized. Most likely, the ketoprofen molecules at or close to the surface of the nanoparticles could deprotonate at these conditions, and had a greater tendency to dissolve.

Two possible mechanisms are proposed for the initial 30% drug release from Eudragit L and Eudragit RS nanoparticles. First, the nanoparticles can contain a larger a proportion of drug at the surface of the particles in comparison to the interior of the particles. Such an uneven distribution could arise from diffusion of the small molecules to the particle surface during the particle preparation and drying process. When such particles are immersed in dissolution medium, the drug at the surface is immediately released, and only further control of drug release is due to the polymers. Second, if the dissolution medium can penetrate to some extent to the polymer matrix, the drug molecules at and close to the surface will dissolve.30,31 Theoretically calculated for a 100-nm nanoparticle, which has a uniform distribution of drug (10% [wt/wt]) and polymer (90% [wt/wt]), medium should be able to initially penetrate to a 5-nm depth to allow 30% drug release. As in the previous case, further control of drug release is controlled by the properties of the polymer.

Conclusion

In this study, it was observed that 2 factors affect the stability of nanoparticles during collection in the aerosol flow reactor method. First, the interactions between the drug and the polymer had an effect on the drug loading of the nanoparticles. For Eudragit L nanoparticles, the solubility of drug in the polymer matrix was the limiting factor for drug incorporation. When the amount of drug in the polymer matrix was higher than the solubility limit of drug in the polymer, crystallization of drug was observed. Second, the thermal properties of the drug-polymer composite nanoparticles affected the stability of the nanoparticles. For the nanoparticles containing Eudragit RS and Eudragit E, the thermal properties of the nanoparticles did not allow collection of dry powders. The drug acted as a plasticizer to the polymers, and the glass transition temperature of the nanoparticles was lowered close to room temperature. Consequently, the mechanical strength of the nanoparticles was lost, which led to coalescence of the nanoparticles.

Acknowledgements

The authors are grateful to Mr Marc Donsmark (Donsmark Process Technology, Fredriksberg, Denmark) for donating the Eudragit materials. The authors wish to thank Mr Raoul Järvinen for his assistance in building the experimental set-up. Prof Heikki Tenhu (University of Helsinki, Department of Chemistry) is acknowledged for DSC and IR analysis equipment time.

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