The study reports bilayered osmotic tablets for sustained co-delivery of isoniazid (INH) and rifampicin (RMP). Polyethylene oxide (PEO) as release retardant was incorporated with INH layer, whereas wicking agent (sodium lauryl sulphate) and buffer (citric acid) were used as solubility enhancer with RMP layer. Bilayered core tablets were coated with cellulose acetate and drilled with two orifices, one at each side. Release profiles of different batches were compared using model dependent and model independent approaches. A significant increase in the release rate of RMP was observed in the presence of buffer and wicking agents. PEO at a concentration of 20 %w/w of total INH core showed zero-order release pattern. Plasticizer concentrations of 1% w/w and membrane thickness of 100 µm were found to be optimum in maintaining the integrity of tablets. Optimized formulation delivered both drugs at approximately zero-order rate up to 24 hrs, independent of pH and agitation rate of the release media. SEM studies showed that coating membrane and orifice maintained their intactness throughout the study period. No interaction between drug and excipients was revealed by DSC study. Formulations, tested for stability at 40±2°C and 75±5% RH for 3 months, were found to be stable.
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