Metabolic studies of ornidazole in the rat, in the dog and in man.

1. Ornidazole, labelled with 14C in the imidazole ring, administered orally to rats, dogs and men was largely excreted in the urine, predominantly as metabolites, with less than 4% of the drug being excreted unchanged. Free and conjugated metabolites were found in the ratio of approx. 1 : 2. 2. The pattern of free ornidazole and metabolites was different in the three species: while ornidazole predominated in man, ornidazole and metabolite M1 in the dog, the most extensive metabolic pattern was found in the rat. 3. The following metabolites were identified: M1, 1-chlorlo-3-(2-hydroxymethyl-5-nitro-1-imidazolyl)-2-propanol; M2, 2-methyl-5-nitroimidazole; M3, N-(3-chloro-2-hydroxypropyl)acetamide: M4, 3-(-2-methyl-5-nitro-1-imidazolyl)-1, 2-propanediol; M5, acetamide. 4. The formation of metabolite M3 and M5 indicated cleavage of the imidazole ring between N-1/C-5 and C-2/C-3. Other ring scissions were not observed. Metabolites carrying a free amino group were not detected. On the basis of the structures identified, a scheme is suggested for the metabolism of ornidazole.