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Study of In‐Vitro Release Characteristics of Carbamazepine Extended Release Semisolid Matrix Filled Capsules Based on Gelucires

Various extended release carbamazepine (CBZ) formulations have been developed previously, in order to reduce the frequency of dosing in chronic therapy and to decrease the variability in drug plasma concentration. In the present study, the suitability of different grades of Gelucires (G, glyceride based excipients) to formulate CBZ extended release capsules by the application of semisolid matrix (SSM) filling capsule technology was investigated. The possible modification of CBZ release kinetics by using Gelucire blends or inclusion of hydrophilic additives in the SSM was studied. The effect of ageing on some selected formulations was also evaluated, using scanning electron microscopy and differential thermal analysis. Twenty‐one capsule formulations were prepared and assessed for their release characteristics. The mechanism of drug release from the test formulations was studied. The following results were obtained: a) Release data could not be correlated to the melting point (mp) of Gelucires used, pointing to relative lipophilicity of the base as a more important determinant of drug release. Among Gelucire grades having melting points higher than 37°C, the release rate proved to be highly dependent on the HLB value and matrix composition. b) CBZ release occurred by different mechanisms, including matrix disintegration, diffusion and or erosion depending on the vehicle employed. c) Zero order release profiles of CBZ were obtained from SSM‐based on G50/13, G53/10 and their blends in ratios higher than 1:1 and G53/10 containing croscarmellose sodium. d) The ageing study revealed that these latter formulations, except those based on G50/13, also showed high dissolution stability during one year of shelf ageing. e) PVP, as a polymorphic transformation inhibitor, can be used to reduce the storage‐induced changes of some grades of Gelucires. From the above data, it can be concluded that different grades of Gelucires and their blends as well as hydrophilic additives could be successfully used to formulate CBZ extended release SSM filled capsules with various release kinetics. The paper has been presented as a poster at the FIP‐World‐Congress, held at Nice, France, September, 2002.