ABSTRACT
The photodecomposition of nisoldipine ((+/-)3-isobutyl-5-methyl-1,4- dihydro-2,6-dimethyl-4-(2-nitrophenyl)-pyridine-3,5-dicarboxylate), whereby its 4-(2-nitrosophenyl) pyridine analogue is obtained as the photolytic product, was investigated under daylight exposure by means of UV derivative spectrophotometry. The optimal instrumental parameters (120 nm/min scan speed; 2 nm slit width; delta gamma = 10 nm and 5 s response time) for analogue derivative spectra were established for amplitudes 1D285 and 2D291 (measured to the baseline) of the nitroso analogue assay, as well as for 1D386 of the parent compound-nisoldipine assay. Using the first-order derivative spectrum, the minimum detectable amount of nitroso analogue in the presence of nisoldipine was equivalent to an impurity level of 5% and by the second-order derivative spectrum, the determination limit was equivalent to an impurity level of 2%. The degradation of nisoldipine followed within 30 days and the calculated maximal degradation rate was 1.6% per day for nisoldipine raw material, but significantly lower values of 0.19 and 0.15% per day were obtained for Nisoldin tablets (10 and 5 mg, respectively).
