Abstract

The physiological disposition of a new orally active antiarrhythmic drug, alpha, alpha-dimethyl-4-(alpha, alpha, beta, beta-tetrafluorophenethyl)benzylamine (MK-251) was investigated in the rat, dog, rhesus monkey, baboon, and man. MK-251 was extensively absorbed after oral administration in all species. Fecal excretion was the major route of tracer elimination in the rat (70%) and dog (80%), whereas the monkey, baboon, and man excreted the majority of the dose via the urine (40-80%). MK-251 and/or its metabolites were widely distributed in rat tissues and exhibited tissue/plasma ratios greater than one in most instances. The lung, liver, and kidney possessed a high tissue affinity for drug and metabolites. The plasma and urinary profile of radioactivity indicated extensive metabolism of MK-251 in all species. Less than 5% of the plasma and urinary radioactivity was identified as unchanged drug. In spite of extensive metabolic transformations, a remarkable feature of this drug is its persistence in the plasma for long periods of time. This is thought to be due to tissue affinity. The metabolic pattern for MK-251 was essentially the same in all species. The major metabolites present in the plasma and the urine were identified as the carbinol analog of MK-251, 2-[4-(alpha, alpha, beta, beta-tetrafluorophenethyl)phenyl]-2-propanol (I), and its glucuronide conjugate. Other metabolites characterized in the urine and plasma were: the N-glucuronide of MK-251, 2-[4-(alpha, alpha, beta, beta-tetrafluorophenethyl)phenyl]propene (II), 2-nitro-2-[4-(alpha, alpha, beta, beta-tetrafluorophenethyl)phenyl]propane (III), alpha, alpha-dimethyl-4-(alpha, alpha, beta, beta-tetrafluorophenethyl)benzyl methyl ether (IV-1) and 4-(alpha, alpha, beta, beta-tetrafluorophenethyl), acetophenone (IV-2). Two minor urinary metabolites were tentatively identified as the N-hydroxy analog of MK-251 and the glycol analog of carbinol I. The in vivo formation of the methyl ether represents the first report of alkylation of a tertiary alcohol.