Matrix tablets were prepared by direct compression using blends of xanthan gum (XG) and guar gum (GG). Diethylcarbamazine (DEC) was used as model drug. Sufficient quantities of materials were weighed to make provision for up to 1080 tablets for 27 batches (40 tablets per batch at a target weight of 500mg each. The individual polymers (Guar gum and Xanthan gum ) were included in the formulation in various proportions (10% to 40 % w/w) while their combinations were employed in the ratio of 30%w/w.Drug release studies were conducted under conditions mimicking mouth-to-colon transit. The dissolution medium consisted of 500 ml 0.1 mol/l HCl kept for 2h, replaced by 500 ml phosphate buffer, pH 7.4 for 3 h, kept at 37±0.5 oC and stirred at 100 rpm, using USP dissolution apparatus 1.Samples were withdrawn at the end of the specified periods (1h,2h,4h,5h,8h,10h,12h,and16h),filtered and assayed spectrophotometrically for diethylcarbamazine, at 250 nm in 0.1 mol/l HCl and 320 nm in pH 7.4 buffer. In order to investigate the release kinetics the dissolution data were fitted into different kinetic models namely zero order, first order and Higuchi models. Korsemeyer et al model was used to determine the mechanism of release. To assess the susceptibility of the prepared DEC delivery systems to the enzymatic action of colonic bacteria, drug release studies were continued in PBS pH 6.8 in the absence (control) and presence of rat caecal contents since these are known to have similar contents to those of human colon. The release study was continued for up to 24h. Samples were withdrawn at different times (6, 8, 10, 12, 16 and 24 h), and assayed spectrophotometrically for DEC at 270 nm. The same volume of fresh dissolution medium was added to restore the initial volume of the dissolution medium after each sample withdrawal. The tablets from various batches exhibited good mechanical properties in terms of hardness, friability, diameter and thickness. Based on in vitro studies, optimum release was observed with formulations containing xanthan gum alone ( 30% w/w and 40% w/w) and in combination (formulation containing xanthan gum 22.5%:guar gum 7.5%, Xanthan 22.5%:). XG 30 % followed first order kinetics via fickian mechanism, while XG 40 % released the drug by zero order kinetics via non-fickian mechanism. The formulations with polymer combinations release the drug fitted best to higuchi kinetics via fickian mechanism. .Presence of xanthan gum in combination with guar gum in the tablets retarded the initial release of drugs from the tablets due to high swelling, which made them more vulnerable to digestion by the microbial enzymes in the colon. Significant difference was observed between drug release in dissolution medium with and without rat cecal contents for al the batches of diethylcarbamazine tablets (P<0.05).
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