PHOTOCHEMICAL SENSITIZATION BY AZATHIOPRINE AND ITS METABOLITES—II. AZATHIOPRINE AND NITROIMIDAZOLE METABOLITES

— The photochemical reactivity of the immunosuppressant drug, azathioprine (AZT) and two representative metabolites of the nitroimidazole moiety, 1-methyl-4-nitroimidazole (MNI) and lmethyl-4-nitro-5-thioimidazole (MNTI) has been examined. No transient species of AZT were observed by laser flash photolysis, inferring a low triplet yield or its rapid deactivation. Consequently AZT, MNI and MNTI displayed little or no photodynamic sensitization via photooxidation reactions. However, AZT and MNI are highly reactive radical scavengers when photoexcited, as determined by reaction with polyacrylamide radicals. The photoreactivity of the metabolites of AZT is greater than that of the parent drug. an observation which may be relevant to the photocarcinogenicity of AZT.