Effect of Microencapsulation on Photo-Stability of Nifedipine

Nifedipine (NIF), a 1,4-dihydropyridine calcium channel antagonist, undergoes photo-degradation to dehydro-nifedipine (DNIF) upon exposure to ultraviolet (UV) light and to the nitroso analogue of dehydro-nifedipine (NDNIF) when exposed to sunlight or some kinds of artificial lights. NIF photo-degradation products do not contribute to clinical activity, thus prevention of photo-degradation of NIF formulations is very important. Large differences in photo-stability between bioequivalent NIF products could potentially result in the therapeutic failure of unstable preparations. The aim of this study was to evaluate the effect of microencapsulation on nifedipine photo-stability. Four different microspheres of nifedipine were prepared using ethyl cellulose, ethyl cellulose plus titanium oxide, pectin and gelatin. Microspheres were exposed to fluorescent light and the content of NIF, DNIF and NDNIF for each product was measured using a specific and sensitive reversed phase high-pressure liquid chromatography (HPLC) method to determine the extent of photo-decomposition. In addition, photo-degradation of pure NIF powder was compared with acidic and buffer solution of NIF. Solution of NIF degraded in one day, while microencapsulation of NIF prevented the photo-degradation for up to six days against light exposure. Therefore, it may be concluded that present microencapsulation method without using other compounds such as opaque materials do not provide enough protection.