Identification of urinary metabolites of penticainide in the rat, dog, baboon and man

[14C]‐Penticainide, 2‐[2‐(diisopropylamino) ethyl]‐4‐methyl‐2‐(2‐pyridyl)pentanamide, a new antiarrhythmic agent, was administered as a single oral dose to rats, dogs, baboons (30 mg kg−1) and to healthy, informed volunteers (300 mg). Excretion of radioactivity was followed for 3 days in urine and faeces. In man, about 95% of the administered radioactivity was eliminated in the urine and levels ranging from 56 to 86% were observed in animals. The radioactivity that did not appear in the urine was almost quantitatively recovered in the faeces. Metabolites in urine were isolated by thin‐layer chromatography and identified by mass spectrometry and nuclear magnetic resonance. In addition to the unchanged drug, nine metabolites and an artifact compound resulting from the partial degradation of one metabolite, were identified among the thirteen radioactive compounds detected. The major metabolites resulted from N‐dealkylation of the diisopropyl moiety, oxidation of the isobutyl side‐chain and hydrolytic cleavage of the amide. Comparison of the excretion and metabolic patterns of animals with those of man revealed that the dog should be a most suitable model for predicting the pharmacological and toxicological effects of penticainide in man.