Degradation kinetics of vincristine sulphate and vindesine sulphate in aqueous solutions

The degradation kinetics of the antineoplastic drugs, vincristine and vindesine, have been studied in the pH range from ? 2 up to 11 at 80°C. A stability-indicating HPLC system with UV detection was utilized for the analysis of vincristine and vindesine in the reaction solutions. The influences of external factors (e.g. pH, buffer concentrations, ionic strength and temperature) on the degradation rate have been studied systematically. The relationship between pH and log k_obs was modelled by using a non-linear least-squares curve-fitting computer program. From this plot thepK_a values of vindesine have been calculated. This plot also showed that vincristine was most stable at pH 4.8 and vindesine at pH 1.9.