Photo- and radiostability of some 1,4-dihydropyridine derivatives in the solid state.

The effect of UV (254 nm) and beta-irradiation at doses 10-100 kGy on physical and chemical properties of four 1,4-dihydropyridyne derivatives in the solid state (nifedipine, nitrendipine, felodipine and nimodipine) has been studied. It has been established that the irradiation causes the appearance of free radicals (EPR) and decomposition products (TLC, GC), a decrease in the melting point (DSC) and the content (GLC, IR) and an increase in microbiological purity. The changes appear faster under the effect of UV than by beta-irradiation and their intensity and character depend on the derivative and dose. The most sensitive to UV irradiation is nifedipine (about 300 times more sensitive than the most resistant nimodipine), while the most sensitive to beta-irradiation is felodipine (about twice as sensitive as the most resistant nitrendipine). The results of our study indicate that 1,4-dihydropyridyne derivatives in solid state can be safely subjected to sterilization by beta-irradiation at doses < 20 kGy.