Free radicals in irradiated drugs: An EPR study

Exposure of dry powder forms of the drugs nitrendipine, nifedipine, felodip ine, and nimodipine to gamma-radiation results in the formation of free rad icals detected by electron paramagnetic resonance (EPR) spectroscopy. The f our structurally related drugs show qualitatively identical EPR spectral fe atures in terms of g-values, the qualitative descriptive parameter. These r adicals are very stable, surviving long periods of time in excess of 9 mont hs and possibly beyond conventional shelf-life of the drugs. The residual r adical population is high enough to be detectable after long storage. Admin istration of such radiation-treated drugs may present patients with quantit ies of free radicals and possibilities of secondary cell damage.