Smart spectrophotometric methods for stability assessment of two co-formulated antigout drugs.

Simple, sensitive and accurate stability indicating spectrophotometric methods have been developed for the simultaneous determination of probenecid, colchicine as well as colchicine degradation product in their ternary mixture. Probenecid was firstly assayed using the double divisor ratio spectra derivative method. On the other hand, three spectrophotometric methods, namely: ratio difference, derivative ratio and mean centering of ratio spectra, have been suggested for the simultaneous quantification of colchicine and its degradation product. The obtained calibration curves were linear at 2.5-30.0 µg/mL, 0.5-25.0 µg/mL and 1.0-13.0 µg/mL for probenecid, colchicine and colchicine degradation product, respectively. The investigated methods were validated in accordance with the International Council for Harmonisation guidelines and were effectively used for quantification of probenecid and colchicine in their bulk powders and combined pharmaceutical dosage form.