EPR investigation of gamma-irradiated anti-emetic drugs

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate the gamma-radiation damage in the microcrystalline powder form of two anti-emetic drugs, namely 4-amino-5-chloro-N-[2-(diethylamino)ethyl]-2-methoxy benzamide monohydrochloride monohydrate (metoclopramide) and 9-tetrahydro-9-methyl-3-[(2-methyl-1H-imidazol-1-yl)methyl]-4H-carbazol-4-one monohydrochloride dihydrate (odansetron). EPR measurements proved that both of them contained various stable paramagnetic species after irradiation and relative yielding of free radicals depends on the absorbed dose. The metoclopramide drug exhibited very weak EPR signals before irradiation. Some spectroscopic properties and suggestions concerning possible structure of the radicals are discussed in this paper.