A New Approach to Evaluating Photo-Stability of Nifedipine and Its Derivatives in Solution by Avtinometry

抄録

The photo-stability of nifedipine and its 4- or 1, 4-substituted derivatives in methanol was studied. A ferrioxalate actinometer was used to measure cumulative numver of photons as an index of light intensity. Under irradiation with a high-pressure mercury lamp, the photo-stability decreased in the order : l-hydroxy-4-(m-nitrophynyl) compound, 4-(p-nitrophenyl) compound, 4-(m-nitrophynyl) compound, l-methyl-4-(o-nitrophynyl) compound and nifedipine itself. The 4-phenyl compound and 4-(o-chlorophenyl) compound did not decompose in the range to 4×10²¹ quanta. Further, the photo-stability of nifedipine was quantitatively examined under sunlight, a fluorescent lamp and a high-pressure mercury lamp. The slopes of the linear plots of residual percent against cumulative number of photons irradiated through a UV-D33S colored glass filter were essentially the same for all three light sources. On the other hand, the slopes did not agree in the case of direct exposure without a filter. A good correlation between extent of photo-degradiation and integrated illumination (lux×h) was not observed with or without the filter. By means of this actinometry with a UV-D33S colored glass filter, the l-hydroxy-4-(m-nitrophenyl) compound and 4-(m-nitrophenyl) compound were quantitatively estimated to be more photo-stable than nifedipine by factors of 270 and 76, respectively, under a given light source.