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Cross-linking of hard gelatin carbamazepine capsules: effect of dissolution conditions on in vitro drug release
European Journal of Pharmaceutical Sciences 19 (2003) 129–132 www.elsevier.com / locate / ejps
Cross-linking of hard gelatin carbamazepine capsules: effect of dissolution conditions on in vitro drug release Herve´ Marchais a , *, Guillaume Cayzeele a , Jean-Yves Legendre b , Mohamed Skiba a , Philippe Arnaud a a
´ ´ , 22 Boulevard Gambetta, Laboratoire de Pharmacie Galenique et Biopharmacie, ADEN-UPRES EA 3234, UFR de Medecine-Pharmacie 76183 Rouen Cedex, France b ´ Recherche, Centre de Recherche Charles Zviak, 90 Rue du General ´ ´ Roguet, 92583 Clichy Cedex, France L’ Oreal Received 16 July 2002; received in revised form 28 February 2003; accepted 21 March 2003
Abstract The aim of this study was to determine if the use of both enzyme and surfactant in the dissolution medium changes the in vitro drug release from cross-linked hard gelatin capsules containing a water-insoluble drug. Hard gelatin capsules were cross-linked by a controlled exposure to formaldehyde resulting in different stressed capsules and carbamazepine (CBZ) was chosen as a drug model. In vitro dissolution studies were conducted using simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) with enzymes. Sodium lauryl sulfate (SLS) was added in the dissolution medium at a concentration of 2% m / v both in SGF and SIF with pepsin and pancreatin, respectively. The percentage of CBZ dissolved was reduced by increasing the degree of gelatin cross-linking. For unstressed hard gelatin capsules, 36% of the CBZ was released after 1 h, lowering to 5% for highly stressed hard gelatin capsules in the SGF. A similar effect was observed with SIF. In the case of moderately stressed hard gelatin capsules, addition of enzyme in the dissolution medium enhanced the percentage of CBZ dissolved. The dissolution level increased from 12% to 39% in SGF with pepsin for hard gelatin capsules cross-linked with 1500 ppm formaldehyde. On the contrary, the use of enzyme in the dissolution medium did not increase the dissolution of CBZ from highly stressed hard gelatin capsules. Surprisingly, the addition of SLS in the medium did not allow the release of the CBZ both in SGF and in SIF. The results of this study demonstrate that the use of enzyme in the dissolution medium is justified for moderately cross-linked hard gelatin capsules. However, the action of a surfactant added in the medium containing enzyme remains unclear. 2003 Elsevier Science B.V. All rights reserved. Keywords: Hard gelatin capsule; Cross-linking; Carbamazepine; Dissolution with sodium lauryl sulfate; Enzymes
1. Introduction Under certain conditions of storage (high humidity and / or elevated temperature) or exposition of trace amounts of aldehydes, gelatin can become cross-linked (or stressed) (Chafetz et al., 1984; Murthy et al., 1989a). This causes the formation of a rubbery translucent film around the hard gelatin capsule (HGC) shell observed during the in vitro dissolution test, because gelatin became partially insoluble in water (Digenis et al., 1994). This water-insoluble gelatin thin film acts as a barrier, restricting drug release. Brown et al. (1998) investigated the in vitro dissolution of hard gelatin acetaminophen capsules stressed by contact with lactose containing 20 ppm formaldehyde. These moderate*Corresponding author. Permanent address: Laboratoire de Pharmacie ´ Galenique, U.F.R. des Sciences Pharmaceutiques, 31 Avenue Monge, 37200 Tours, France. Tel.: 133-2-4736-7197; fax: 133-2-4736-7198. E-mail address: [email protected] (H. Marchais).
ly stressed capsules failed the USP dissolution specifications for acetaminophen capsule when tested in water and simulated gastric fluid without enzyme but passed with addition of pepsin. Guyot et al. (1989) studied the in vitro release of theophylline from cross-linked hard gelatin capsules in order to obtain a sustained release form. They showed that the amount of drug released was lowered when the cross-linking reaction time increased. In the same way, Meyer et al. (2000) studied the effect of different cross-linking conditions on the in vitro dissolution of hard and soft gelatin acetaminophen capsules and if the results are predictive of changes in the bioavailability of the capsules in humans. The in vitro rate of dissolution dramatically decreased when the degree of cross-linking increased and moreover, capsules stressed to the greatest extent were not bioequivalent to the unstressed control capsules. Some published reports suggest that the presence of enzymes in the test medium accelerate the dissolution of
0928-0987 / 03 / $ – see front matter 2003 Elsevier Science B.V. All rights reserved. doi:10.1016 / S0928-0987(03)00070-8
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H. Marchais et al. / European Journal of Pharmaceutical Sciences 19 (2003) 129–132
the pellicle and cause subsequent release of the drug (Murthy et al., 1989b). Hence, it has been proposed a second dissolution test when capsules do not conform to the dissolution specification (USP24-NF19, 2001). This second dissolution test was performed using a medium (e.g. water) with addition of purified pepsin (pH medium less than 6.8) or pancreatin (pH medium of 6.8 or greater). However, for sparingly water-soluble drugs, aqueous media commonly used are not suitable. Different strategies have been proposed to conduct dissolution testing for water-insoluble drugs by using a large volume of aqueous medium or hydroalcoholic dissolution media. Another approach involves increasing the drug solubility by addition of varied surfactants (e.g. sodium lauryl sulfate, bile salts, polyoxyethylene sorbitan, etc.) in the dissolution media (Shah et al., 1989). To our knowledge, no studies have been conducted using both enzyme and surfactant in the dissolution medium. The purpose of this work was to evaluate if the USP second dissolution test modified the in vitro release profile of cross-linked hard gelatin capsules containing carbamazepine and to assess the effect of sodium lauryl sulfate added to the dissolution media and a possible interaction with enzymes.
2. Materials and methods
2.1. Materials Carbamazepine was obtained from Novartis-Pharma. Lactose powder and SLS were purchased from Cooper (Melun, France). Pepsin with an activity level of 2000– 2400 units / mg protein and pancreatin USP (both porcine source) were of analytical reagent grade (ICN Pharmaceuticals, Orsay, France). Capsules were Coni-Snap type (Capsugel, Colmar, France). SIF and SGF were prepared according to the specifications of the USP24 (USP24, 2001).
2.2. Cross-linking hard gelatin capsules The method of stressing hard gelatin capsule shells was adapted from a technique previously described by Brown et al. (1998). The procedure involves exposure of lactose powder to formaldehyde vapour in a desiccator for 12 h. The accurate measurement of formaldehyde content was determined using the method described in the European Pharmacopoeia (4th ed., 2002). Appropriate dilution of lactose treated samples with pure lactose gave various formaldehyde levels ranging from 100 to 4000 ppm. Formaldehyde contaminated with lactose was filled into size 1 hard gelatin capsules, which were stored for 6 days in the dark at room temperature. The stressed capsules were then emptied, and finally stressed and unstressed capsules were filled with a blend of 100 mg of carbamazepine and pure lactose.
2.3. In vitro dissolution study Dissolution was performed using a USP Apparatus 2 (Erweka DT6, Heusenstamm, Germany). In a preliminary study, dissolution tests were done with unstressed hard gelatin capsules in order to investigate the effect of SLS concentration in the medium on dissolution of CBZ. Studies were conducted in 1000 ml of SGF and SIF without enzymes at 37 8C. The paddle rotation speed was 100 rpm. Two amounts of SLS (0.5 and 2% w / v) were assessed. A control (without SLS) was conducted under the same conditions. To avoid floating, the capsules were ballasted by using a wire. The dissolution medium was continuously pumped, filtered through a 10-mm pore size polypropylene filter and monitored at 280 nm with an automatic UV sampler (Safas 210, Safas, Monaco). Data were computed with a standard calibration curve of the drug (r50.998) and the values obtained were the mean of six determinations. The percentage of CBZ dissolved was measured after 60 min, based on labelled amounts per capsule. Various stressed capsules were tested in order to study the influence of cross-linking on the release of CBZ. The experimental conditions were the same as above. In case the enzymes were used, the pepsin concentration was 3.2 g / l in SGF and pancreatin concentration was 10 g / l in SIF. In some experiments, SLS was added at a concentration of 2% w / v in the dissolution medium. Controls were done using unstressed capsules. In order to avoid possible UV interference from enzymes, blank medium (without drug) was analysed in the same conditions and subtracted from the sample.
3. Results and discussion
3.1. Effect of surfactant on dissolution of carbamazepine unstressed hard gelatin capsules The influence of SLS on the dissolution of carbamazepine is shown in Table 1. If no surfactant was added in the dissolution medium, the percentage of CBZ released at 60 min was 36 and 34% with SGF and SIF, respectively.
Table 1 In vitro dissolution release of carbamazepine from unstressed hard gelatin capsules in the presence of SLS (mean6S.D.; n56) Dissolution media SGF SGF10.5% SLS SGF12% SLS SIF SIF10.5% SLS SIF12% SLS
CBZ percent dissolved 15 min
30 min
45 min
60 min
2263 2363 4067 2064 2863 45610
2866 3364 5667 2768 3064 6269
3368 4064 6766 30610 3565 70610
3669 4564 7365 34612 3966 7368
H. Marchais et al. / European Journal of Pharmaceutical Sciences 19 (2003) 129–132
With an SLS concentration of 0.5% w / v, the amount released increased slightly (45 and 39%, respectively). In contrast, increasing the amount of SLS up to 2% w / v, the percentage of dissolution dramatically increased to 73% for the two media. These results are in accordance with Shah et al. (1989) who showed that the rate and extent of dissolution of CBZ tablets increased with an increase of SLS concentration in the dissolution medium. In addition, it can be observed that the nature of the dissolution medium used (SGF or SIF) had no significant influence on the dissolution profile of CBZ.
3.2. Effect of the degree of cross-linking on dissolution of carbamazepine stressed hard gelatin capsules First, the tests were conducted in SGF without enzyme and surfactant (Fig. 1). As expected, the results clearly show that the amount of CBZ dissolved was dramatically reduced with increasing degree of gelatin cross-linking. When HGC was stressed with 100 ppm formaldehyde (slightly stressed), the percentage of CBZ released was lowered to 26% at 60 min. This value decreased to 10% when capsules were subjected to 1500 ppm formaldehyde (moderately stressed). Finally, no dissolution occurred if the capsules were treated with 4000 ppm formaldehyde (highly stressed). For acetaminophen cross-linked HGC, Meyer et al. (2000) have shown that moderately stressed HGC exhibited a drug dissolution percentage after 45 min of 52% in SGF lowering to 1% for highly stressed HGC. In comparison, the percentage of drug dissolved was 99% for unstressed control HGC. These data confirmed that the degree of gelatin cross-linking influenced the rate of in vitro drug release in the case of a sparingly water-soluble drug. In a second set of experiments, pepsin was added in the dissolution medium in order to enhance the amount of drug dissolved (Fig. 1). The percentage of CBZ dissolved increased to 26–29% for moderately stressed HGC (1000–
Fig. 1. Effect of the degree of cross-linking HGC on the percentage of CBZ dissolved after 60 min in the simulated gastric fluid without and with pepsin (mean6S.D.; n56).
131
1500 ppm) but could not reach the value observed (36%) for the control (unstressed HGC). Despite the use of enzyme, the amount of CBZ dissolved in 60 min remained low (respectively 7 and 3%) with the highly stressed HGC (2000–4000 ppm). The amount of pepsin was not sufficient to reach the initial dissolution profile. In the same manner, dissolution tests were conducted in SIF without and with pancreatin in order to evaluate the effect of the nature of dissolution medium (Fig. 2). When the pH was increased from 1.2 (SGF) to 7.5 (SIF), the dissolution rate was not modified with unstressed HGC (36% vs. 34%). CBZ dissolution may be considered as a non-pH dependant phenomenon (Jung et al., 1997). The addition of pancreatin in SIF enhanced the dissolution extent for the moderately (1500 ppm) and highly (2000 ppm) stressed HGC (39 and 31%, respectively), but not for the highest degree of cross-linking (4000 ppm) for what the percentage of CBZ dissolved remain close to 0%.
3.3. Effect of surfactant and enzymes on dissolution of carbamazepine stressed hard gelatin capsules To determine the drug release profile of water-insoluble drug dosage forms, Shah et al. (1989) have recommended the use of a surfactant rather than adding organic solvents to the dissolution medium. When using a two-tier dissolution test, the question is how the enzymes may interfere with the surfactant. Experiments were conducted with moderately stressed (1500 ppm) HGC both in SGF and SIF with enzymes and 2% m / v SLS (Fig. 3). Surprisingly, no dissolution of CBZ occurred despite the presence of pepsin or pancreatin in the medium. A possible explanation may be the existence of an interaction between SLS and the enzymes not allowing capsule disintegration. To our knowledge there is a lack of previous studies using both surfactant and enzymes in the dissolution media.
Fig. 2. Effect of the degree of cross-linking HGC on the percentage of CBZ dissolved after 60 min in the simulated intestinal fluid with and without pancreatin (mean6S.D.; n56).
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H. Marchais et al. / European Journal of Pharmaceutical Sciences 19 (2003) 129–132
Fig. 3. Effect of the use of enzymes and surfactant in the dissolution media on the percentage of CBZ dissolved after 60 min from moderately (1500 ppm) cross-linked HGC (mean6S.D.; n56).
Acknowledgements The authors would like to thank Ms O. Lopez for her helpful technical assistance.
References Brown, J., Madit, N., Cole, E.T., Wilding, I.R., Cade, D., 1998. The effect of cross-linking on the in vivo disintegration of hard gelatin capsules. Pharm. Res. 15, 1026–1030.
Chafetz, L., Hong, W., Tsilifonis, D.C., Taylor, A.K., Philip, J.J., 1984. Decrease in the rate of capsule dissolution due to formaldehyde from polysorbate 80 auto-oxidation. J. Pharm. Sci. 73, 1186–1187. Digenis, G.A., Gold, T.B., Shah, V.P., 1994. Cross-linking of gelatin capsules and its relevance to their in vitro–in vivo performance. J. Pharm. Sci. 83, 915–921. European Pharmacopoeia, 4th Edition, 2002. Limit Tests—Formaldehyde, p. 96. Guyot, M., Fawaz, F., Maury, M., 1989. In vitro release of theophylline from cross-linked gelatin capsules. Int. J. Pharm. 144, 209–216. Jung, H., Milan, R.C., Girard, M.E., Leon, F., Montoya, M.A., 1997. Bioequivalence study of carbamazepine tablets: in vitro / in vivo correlation. Int. J. Pharm. 152, 37–44. Meyer, M.C., Straughn, A.B., Mhatre, R.M., Hussain, A., Shah, V.P., Bottom, C.B. et al., 2000. The effect of gelatin cross-linking on the bioequivalence of hard and soft gelatin acetaminophen capsules. Pharm. Res. 17, 962–966. Murthy, K.S., Enders, N.A., Fawzi, M.B., 1989a. Dissolution stability of hard-shell capsule products. Part I: The effect of exaggerated storage conditions. Pharm. Technol. 13, 72–86. Murthy, K.S., Reisch, R.G., Fawzi, M.B., 1989b. Dissolution stability of hard-shell capsule products. Part II: The effect of dissolution test conditions on in vitro drug release. Pharm. Technol. 13, 53–56. Shah, V.P., Konecny, J.J., Everett, R.L., McCullough, B., Noorizadeh, A.C., Skelly, J.P., 1989. In vitro dissolution profile of water-insoluble drug dosage forms in the presence of surfactants. Pharm. Res. 6, 612–618. USP24, 2001. Test Solutions, 2235–2236. USP24-NF19, Supplement 4, 2001. Sect. ,711. Dissolution, 3250– 3252.
Cross-linking of hard gelatin carbamazepine capsules: effect of dissolution conditions on in vitro drug release Herve´ Marchais a , *, Guillaume Cayzeele a , Jean-Yves Legendre b , Mohamed Skiba a , Philippe Arnaud a a
´ ´ , 22 Boulevard Gambetta, Laboratoire de Pharmacie Galenique et Biopharmacie, ADEN-UPRES EA 3234, UFR de Medecine-Pharmacie 76183 Rouen Cedex, France b ´ Recherche, Centre de Recherche Charles Zviak, 90 Rue du General ´ ´ Roguet, 92583 Clichy Cedex, France L’ Oreal Received 16 July 2002; received in revised form 28 February 2003; accepted 21 March 2003
Abstract The aim of this study was to determine if the use of both enzyme and surfactant in the dissolution medium changes the in vitro drug release from cross-linked hard gelatin capsules containing a water-insoluble drug. Hard gelatin capsules were cross-linked by a controlled exposure to formaldehyde resulting in different stressed capsules and carbamazepine (CBZ) was chosen as a drug model. In vitro dissolution studies were conducted using simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) with enzymes. Sodium lauryl sulfate (SLS) was added in the dissolution medium at a concentration of 2% m / v both in SGF and SIF with pepsin and pancreatin, respectively. The percentage of CBZ dissolved was reduced by increasing the degree of gelatin cross-linking. For unstressed hard gelatin capsules, 36% of the CBZ was released after 1 h, lowering to 5% for highly stressed hard gelatin capsules in the SGF. A similar effect was observed with SIF. In the case of moderately stressed hard gelatin capsules, addition of enzyme in the dissolution medium enhanced the percentage of CBZ dissolved. The dissolution level increased from 12% to 39% in SGF with pepsin for hard gelatin capsules cross-linked with 1500 ppm formaldehyde. On the contrary, the use of enzyme in the dissolution medium did not increase the dissolution of CBZ from highly stressed hard gelatin capsules. Surprisingly, the addition of SLS in the medium did not allow the release of the CBZ both in SGF and in SIF. The results of this study demonstrate that the use of enzyme in the dissolution medium is justified for moderately cross-linked hard gelatin capsules. However, the action of a surfactant added in the medium containing enzyme remains unclear. 2003 Elsevier Science B.V. All rights reserved. Keywords: Hard gelatin capsule; Cross-linking; Carbamazepine; Dissolution with sodium lauryl sulfate; Enzymes
1. Introduction Under certain conditions of storage (high humidity and / or elevated temperature) or exposition of trace amounts of aldehydes, gelatin can become cross-linked (or stressed) (Chafetz et al., 1984; Murthy et al., 1989a). This causes the formation of a rubbery translucent film around the hard gelatin capsule (HGC) shell observed during the in vitro dissolution test, because gelatin became partially insoluble in water (Digenis et al., 1994). This water-insoluble gelatin thin film acts as a barrier, restricting drug release. Brown et al. (1998) investigated the in vitro dissolution of hard gelatin acetaminophen capsules stressed by contact with lactose containing 20 ppm formaldehyde. These moderate*Corresponding author. Permanent address: Laboratoire de Pharmacie ´ Galenique, U.F.R. des Sciences Pharmaceutiques, 31 Avenue Monge, 37200 Tours, France. Tel.: 133-2-4736-7197; fax: 133-2-4736-7198. E-mail address: [email protected] (H. Marchais).
ly stressed capsules failed the USP dissolution specifications for acetaminophen capsule when tested in water and simulated gastric fluid without enzyme but passed with addition of pepsin. Guyot et al. (1989) studied the in vitro release of theophylline from cross-linked hard gelatin capsules in order to obtain a sustained release form. They showed that the amount of drug released was lowered when the cross-linking reaction time increased. In the same way, Meyer et al. (2000) studied the effect of different cross-linking conditions on the in vitro dissolution of hard and soft gelatin acetaminophen capsules and if the results are predictive of changes in the bioavailability of the capsules in humans. The in vitro rate of dissolution dramatically decreased when the degree of cross-linking increased and moreover, capsules stressed to the greatest extent were not bioequivalent to the unstressed control capsules. Some published reports suggest that the presence of enzymes in the test medium accelerate the dissolution of
0928-0987 / 03 / $ – see front matter 2003 Elsevier Science B.V. All rights reserved. doi:10.1016 / S0928-0987(03)00070-8
130
H. Marchais et al. / European Journal of Pharmaceutical Sciences 19 (2003) 129–132
the pellicle and cause subsequent release of the drug (Murthy et al., 1989b). Hence, it has been proposed a second dissolution test when capsules do not conform to the dissolution specification (USP24-NF19, 2001). This second dissolution test was performed using a medium (e.g. water) with addition of purified pepsin (pH medium less than 6.8) or pancreatin (pH medium of 6.8 or greater). However, for sparingly water-soluble drugs, aqueous media commonly used are not suitable. Different strategies have been proposed to conduct dissolution testing for water-insoluble drugs by using a large volume of aqueous medium or hydroalcoholic dissolution media. Another approach involves increasing the drug solubility by addition of varied surfactants (e.g. sodium lauryl sulfate, bile salts, polyoxyethylene sorbitan, etc.) in the dissolution media (Shah et al., 1989). To our knowledge, no studies have been conducted using both enzyme and surfactant in the dissolution medium. The purpose of this work was to evaluate if the USP second dissolution test modified the in vitro release profile of cross-linked hard gelatin capsules containing carbamazepine and to assess the effect of sodium lauryl sulfate added to the dissolution media and a possible interaction with enzymes.
2. Materials and methods
2.1. Materials Carbamazepine was obtained from Novartis-Pharma. Lactose powder and SLS were purchased from Cooper (Melun, France). Pepsin with an activity level of 2000– 2400 units / mg protein and pancreatin USP (both porcine source) were of analytical reagent grade (ICN Pharmaceuticals, Orsay, France). Capsules were Coni-Snap type (Capsugel, Colmar, France). SIF and SGF were prepared according to the specifications of the USP24 (USP24, 2001).
2.2. Cross-linking hard gelatin capsules The method of stressing hard gelatin capsule shells was adapted from a technique previously described by Brown et al. (1998). The procedure involves exposure of lactose powder to formaldehyde vapour in a desiccator for 12 h. The accurate measurement of formaldehyde content was determined using the method described in the European Pharmacopoeia (4th ed., 2002). Appropriate dilution of lactose treated samples with pure lactose gave various formaldehyde levels ranging from 100 to 4000 ppm. Formaldehyde contaminated with lactose was filled into size 1 hard gelatin capsules, which were stored for 6 days in the dark at room temperature. The stressed capsules were then emptied, and finally stressed and unstressed capsules were filled with a blend of 100 mg of carbamazepine and pure lactose.
2.3. In vitro dissolution study Dissolution was performed using a USP Apparatus 2 (Erweka DT6, Heusenstamm, Germany). In a preliminary study, dissolution tests were done with unstressed hard gelatin capsules in order to investigate the effect of SLS concentration in the medium on dissolution of CBZ. Studies were conducted in 1000 ml of SGF and SIF without enzymes at 37 8C. The paddle rotation speed was 100 rpm. Two amounts of SLS (0.5 and 2% w / v) were assessed. A control (without SLS) was conducted under the same conditions. To avoid floating, the capsules were ballasted by using a wire. The dissolution medium was continuously pumped, filtered through a 10-mm pore size polypropylene filter and monitored at 280 nm with an automatic UV sampler (Safas 210, Safas, Monaco). Data were computed with a standard calibration curve of the drug (r50.998) and the values obtained were the mean of six determinations. The percentage of CBZ dissolved was measured after 60 min, based on labelled amounts per capsule. Various stressed capsules were tested in order to study the influence of cross-linking on the release of CBZ. The experimental conditions were the same as above. In case the enzymes were used, the pepsin concentration was 3.2 g / l in SGF and pancreatin concentration was 10 g / l in SIF. In some experiments, SLS was added at a concentration of 2% w / v in the dissolution medium. Controls were done using unstressed capsules. In order to avoid possible UV interference from enzymes, blank medium (without drug) was analysed in the same conditions and subtracted from the sample.
3. Results and discussion
3.1. Effect of surfactant on dissolution of carbamazepine unstressed hard gelatin capsules The influence of SLS on the dissolution of carbamazepine is shown in Table 1. If no surfactant was added in the dissolution medium, the percentage of CBZ released at 60 min was 36 and 34% with SGF and SIF, respectively.
Table 1 In vitro dissolution release of carbamazepine from unstressed hard gelatin capsules in the presence of SLS (mean6S.D.; n56) Dissolution media SGF SGF10.5% SLS SGF12% SLS SIF SIF10.5% SLS SIF12% SLS
CBZ percent dissolved 15 min
30 min
45 min
60 min
2263 2363 4067 2064 2863 45610
2866 3364 5667 2768 3064 6269
3368 4064 6766 30610 3565 70610
3669 4564 7365 34612 3966 7368
H. Marchais et al. / European Journal of Pharmaceutical Sciences 19 (2003) 129–132
With an SLS concentration of 0.5% w / v, the amount released increased slightly (45 and 39%, respectively). In contrast, increasing the amount of SLS up to 2% w / v, the percentage of dissolution dramatically increased to 73% for the two media. These results are in accordance with Shah et al. (1989) who showed that the rate and extent of dissolution of CBZ tablets increased with an increase of SLS concentration in the dissolution medium. In addition, it can be observed that the nature of the dissolution medium used (SGF or SIF) had no significant influence on the dissolution profile of CBZ.
3.2. Effect of the degree of cross-linking on dissolution of carbamazepine stressed hard gelatin capsules First, the tests were conducted in SGF without enzyme and surfactant (Fig. 1). As expected, the results clearly show that the amount of CBZ dissolved was dramatically reduced with increasing degree of gelatin cross-linking. When HGC was stressed with 100 ppm formaldehyde (slightly stressed), the percentage of CBZ released was lowered to 26% at 60 min. This value decreased to 10% when capsules were subjected to 1500 ppm formaldehyde (moderately stressed). Finally, no dissolution occurred if the capsules were treated with 4000 ppm formaldehyde (highly stressed). For acetaminophen cross-linked HGC, Meyer et al. (2000) have shown that moderately stressed HGC exhibited a drug dissolution percentage after 45 min of 52% in SGF lowering to 1% for highly stressed HGC. In comparison, the percentage of drug dissolved was 99% for unstressed control HGC. These data confirmed that the degree of gelatin cross-linking influenced the rate of in vitro drug release in the case of a sparingly water-soluble drug. In a second set of experiments, pepsin was added in the dissolution medium in order to enhance the amount of drug dissolved (Fig. 1). The percentage of CBZ dissolved increased to 26–29% for moderately stressed HGC (1000–
Fig. 1. Effect of the degree of cross-linking HGC on the percentage of CBZ dissolved after 60 min in the simulated gastric fluid without and with pepsin (mean6S.D.; n56).
131
1500 ppm) but could not reach the value observed (36%) for the control (unstressed HGC). Despite the use of enzyme, the amount of CBZ dissolved in 60 min remained low (respectively 7 and 3%) with the highly stressed HGC (2000–4000 ppm). The amount of pepsin was not sufficient to reach the initial dissolution profile. In the same manner, dissolution tests were conducted in SIF without and with pancreatin in order to evaluate the effect of the nature of dissolution medium (Fig. 2). When the pH was increased from 1.2 (SGF) to 7.5 (SIF), the dissolution rate was not modified with unstressed HGC (36% vs. 34%). CBZ dissolution may be considered as a non-pH dependant phenomenon (Jung et al., 1997). The addition of pancreatin in SIF enhanced the dissolution extent for the moderately (1500 ppm) and highly (2000 ppm) stressed HGC (39 and 31%, respectively), but not for the highest degree of cross-linking (4000 ppm) for what the percentage of CBZ dissolved remain close to 0%.
3.3. Effect of surfactant and enzymes on dissolution of carbamazepine stressed hard gelatin capsules To determine the drug release profile of water-insoluble drug dosage forms, Shah et al. (1989) have recommended the use of a surfactant rather than adding organic solvents to the dissolution medium. When using a two-tier dissolution test, the question is how the enzymes may interfere with the surfactant. Experiments were conducted with moderately stressed (1500 ppm) HGC both in SGF and SIF with enzymes and 2% m / v SLS (Fig. 3). Surprisingly, no dissolution of CBZ occurred despite the presence of pepsin or pancreatin in the medium. A possible explanation may be the existence of an interaction between SLS and the enzymes not allowing capsule disintegration. To our knowledge there is a lack of previous studies using both surfactant and enzymes in the dissolution media.
Fig. 2. Effect of the degree of cross-linking HGC on the percentage of CBZ dissolved after 60 min in the simulated intestinal fluid with and without pancreatin (mean6S.D.; n56).
132
H. Marchais et al. / European Journal of Pharmaceutical Sciences 19 (2003) 129–132
Fig. 3. Effect of the use of enzymes and surfactant in the dissolution media on the percentage of CBZ dissolved after 60 min from moderately (1500 ppm) cross-linked HGC (mean6S.D.; n56).
Acknowledgements The authors would like to thank Ms O. Lopez for her helpful technical assistance.
References Brown, J., Madit, N., Cole, E.T., Wilding, I.R., Cade, D., 1998. The effect of cross-linking on the in vivo disintegration of hard gelatin capsules. Pharm. Res. 15, 1026–1030.
Chafetz, L., Hong, W., Tsilifonis, D.C., Taylor, A.K., Philip, J.J., 1984. Decrease in the rate of capsule dissolution due to formaldehyde from polysorbate 80 auto-oxidation. J. Pharm. Sci. 73, 1186–1187. Digenis, G.A., Gold, T.B., Shah, V.P., 1994. Cross-linking of gelatin capsules and its relevance to their in vitro–in vivo performance. J. Pharm. Sci. 83, 915–921. European Pharmacopoeia, 4th Edition, 2002. Limit Tests—Formaldehyde, p. 96. Guyot, M., Fawaz, F., Maury, M., 1989. In vitro release of theophylline from cross-linked gelatin capsules. Int. J. Pharm. 144, 209–216. Jung, H., Milan, R.C., Girard, M.E., Leon, F., Montoya, M.A., 1997. Bioequivalence study of carbamazepine tablets: in vitro / in vivo correlation. Int. J. Pharm. 152, 37–44. Meyer, M.C., Straughn, A.B., Mhatre, R.M., Hussain, A., Shah, V.P., Bottom, C.B. et al., 2000. The effect of gelatin cross-linking on the bioequivalence of hard and soft gelatin acetaminophen capsules. Pharm. Res. 17, 962–966. Murthy, K.S., Enders, N.A., Fawzi, M.B., 1989a. Dissolution stability of hard-shell capsule products. Part I: The effect of exaggerated storage conditions. Pharm. Technol. 13, 72–86. Murthy, K.S., Reisch, R.G., Fawzi, M.B., 1989b. Dissolution stability of hard-shell capsule products. Part II: The effect of dissolution test conditions on in vitro drug release. Pharm. Technol. 13, 53–56. Shah, V.P., Konecny, J.J., Everett, R.L., McCullough, B., Noorizadeh, A.C., Skelly, J.P., 1989. In vitro dissolution profile of water-insoluble drug dosage forms in the presence of surfactants. Pharm. Res. 6, 612–618. USP24, 2001. Test Solutions, 2235–2236. USP24-NF19, Supplement 4, 2001. Sect. ,711. Dissolution, 3250– 3252.