Development Of Dissoulution Medium For Rifampicin Sustained Release Formulations

Dissolution of drugs from solid dosage forms is a key parameter during the product development, formulation and through out the product storage. Rifampicin is very stable in the solid state. Rifampicin transforms into rifampin quinone in mildly alkaline solutions and in presence of atmospheric oxygen at room temperature. The main decomposition product of rifampicin in aqueous acidic medium was 3-formyl rifampicin SV. The decomposition of rifampicin in aqueous solution is diminished by the addition of reducing agents such as ascorbic acid and sodium ascorbate. In USP, 0.1 N HCI is an official dissolution medium and the amount of rifampicin was estimated in comparison with a standard solution having a known concentration of rifampicin concomitantly held at the same temperature for the time specified. This is not suitable for studying release kinetics of controlled release formulations. For this reason, stability of rifampicin in different aqueous fluids and buffers of varying pH in the presence of ascorbic acid as reducing agent was studied. The results indicated that rifampicin was more stable in phosphate buffer of pH 7.4 containing 0.02% w/v of ascorbic acid. Drug release studies of commercial products were done by using this medium and they were compared with the official USP method. This medium was found to be more suitable for studying rifampicin controlled release formulations.