Hydrolytic degradation of nitrendipine and nisoldipine
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The development of a new HPLC-UV diode array procedure applied to follow the hydrolytic degradation of two well-known 4-nitrophenyl-1,4-dihydropyridine derivatives, nitrendipine and nisoldipine is reported. Hydrolysis of each drug were carried out in ethanol/Britton-Robinson buffer at different pHs, stored into amber vials at controlled temperatures of 40, 60 and 80 degreesC and periodically sampled and assayed by HPLC. Nitrendipine degradation in different parenteral solutions was also evaluated. The HPLC procedure exhibited an adequate selectivity, repeatability (< 1%) and reproducibility (< 2%). The recoveries were higher than 98% with CV of 1.13 and 1.54% for nitrendipine and nisoldipine, respectively. A significant degradation was observed at alkaline pH (> pH 8) with a first order kinetic for both drugs. At pH 12, 80 degreesC, k values of 3.56 x 10(-2) h(-1) and 2.22 x 10(-2) for nitrendipine and nisoldipine, respectively were obtained. Also, activation energies of 16.8 and 14.7 kcal mol(-1) for nitrendipine and nisoldipine, respectively, were calculated. Furthermore, from the results obtained from hydrolytic degradation in different solutions for parenteral use, we can affirm that solutions significantly increased the degradation of nitrendipine. In conclusion, the HPLC proposed procedure exhibited adequate analytical requirements to be applied to the hydrolytic degradation studies of nitrendipine and nisoldipine. Furthermore, all tested parenteral solutions significantly increased the hydrolytic degradation of nitrendipine, the composition of solution being a relevant factor.