A selective voltammetric method to follow the hydrolytic degradation of nitrendipine and nisoldipine
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The development and application of a differential pulse voltammetric procedure for the hydrolytic degradation kinetic study of two well-known 1,4-dihydropyridine type drugs, nitrendipine and nisoldipine are presented. The DPV procedure exhibited an adequate selectivity, repeatability and reproducibility with CV lower than 2%. The recoveries were higher than 98% with CV of 1.63% and 1.87% for nitrendipine and nisoldipine, respectively. Hydrolysis of each drug was carried out in ethanol/Britton-Robinson buffer (30/70) at different pHs and at Controlled temperature of 40, 60 and 80 C. A significant degradation was observed at alkaline pH (> pH 8) following a first order kinetic for both drugs. At pH 12 the decay constant values of 4.85 x 10(-2) h(-1) for nitrendipine and 3.18 x 10(-2) h(-1) for nisoldipine were obtained. Also, activation energies of 18 kcal/mol and 16 kcal/mol for nitrendipine and nisoldipine, respectively, were calculated. Furthermore, for the nitrendipine hydrolytic, degradation test in different solutions for parenteral use were studied. All the tested vehicles significantly increased the degradation of the drug, with the composition of solutions being the most relevant factor rather than the pH.