Development of a stability-indicating HPLC method for simultaneous determination of olanzapine and fluoxetine in combined dosage forms.

A stability-indicating high-performance liquid chromatography method is developed for analysis of olanzapine and fluoxetine in the presence of their degradation products generated from forced decomposition studies as prescribed by the International Conference on Harmonization. Hydrolysis, oxidation, photolysis, and thermal degradation are evaluated by subjecting the drug substances to stress conditions. Successful separation of drugs from degradation products is achieved on a reversed-phase C(18) column using 75 mM potassium dihydrogen phosphate buffer (pH 4.0)-acetonitrile-methanol (55:40:5, v/v/v) as the mobile phase. The flow rate is 0.8 mL/min, and the detection wavelength is 227 nm. The method is validated with respect to linearity, precision, accuracy, system suitability, and robustness. The utility of the procedure is verified by its application to marketed formulations that are subjected to accelerated stability studies. Good separation of the drugs and their degradation products is observed using this method. The products formed in marketed tablet dosage forms are similar to those formed in standard drug solutions under similar stress conditions.