The fate of 4-cyanoacetanilide in rats and mice; mechanism of formation of a novel electrophilic metabolite.

1. The metabolic fate of 4-cyanoacetanilide (CAA), labelled with 14C and 13C in the N-acetyl group, was studied in rats (oral dose, 22.5 mg/kg) and mice (oral dose 21.7 mg/kg). 2. The metabolic profile in the urine of rats was compared with that obtained previously with 4-cyano-N,N-dimethylaniline (CDA) and confirms the intermediacy of CAA in the metabolism of CDA. 3. The precursor of a major metabolite of CDA and CAA (the mercapturic acid N-acetyl-S-[2-keto-2-(4-cyanoanilino)ethyl]cysteine, metabolite C) was identified in the urine of CAA-dosed rats as the O-sulphate conjugate of N-(4-cyanophenyl)glycolamide. 4. Pretreatment of rats with the sulphotransferase inhibitor pentachlorophenol reduced the yield of the mercapturic acid metabolite C, further indicating the intermediacy of a sulphate conjugate. 5. Metabolite C was not formed from CAA by mice; thus, this species difference, also observed with CDA, occurs at the level side-chain (acetyl) hydroxylation as well as at N-acetylation of 4-cyanoaniline as previously proposed. 6. The significance of this pathway as a bioactivation reaction of CDA, CAA and other acetanilides is discussed.