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Background and purpose: One of the methods of preparing controlled-release dosage forms is the incorporation of drug in a matrix containing a hydrophilic rate-controlling polymer. Drug-polymer ratio, drug particle size and HPMC particle size have been identified as modifiers of drug release. This study evaluated the relationship and influence of formulation factors such as drug-HPMC ratio and particle size of drug and HPMC on drug release from matrices containing HPMC K 15 M and thophylline as model drug. Materials and methods: Theopylline tablets were obtained by the direct compression method using different particle sizes and ratio of theophylline and HPMC K15M. The physicochemical properties of prepared tablets were investigated. Drug release rate was also studied using USP I dissolution apparatus at pH 1.2 and 7.2. From different formulations the theopylline release was analyzed and then the data was fitted to Kinetic models. Results: The results of the present study showed that the rates of theophylline release from HPMC K15 M matrices are mainly controlled by the drug-HPMC ratio. The drug and HPMC particle size also influenced the drug release parameters, although to a lesser extent. Conclusion: The main factor influencing the drug release from formulations is the polymer content. There is direct relationship between the polymer particle size and drug release. However, there is an inverse relationship between the drug particle size and release of theophylline.

Keywords: Theophylline, polymer, particle size, release rate

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