Pharmacokinetics and metabolism of dofetilide in mouse, rat, dog and man

1. Pharmacokinetics of dofetilide were studied in man, dog, rat and mouse after single i.v. and oral doses of dofetilide or 14C-dofetilide. 2. Dofetilide was absorbed completely in all species. Low metabolic clearance in man resulted in complete bioavailability following oral administration. Higher metabolic clearance in rodents, and to a lesser extent dogs, resulted in decreased bioavailability because of first-pass metabolism. 3. Following i.v. administration, the volume of distribution showed only moderate variation in all species (2 8-6 3***1/kg). High plasma clearance in rodents resulted in short half-life values (mouse 0 32, male rat 0 5 and female rat 1 2 h), whilst lower clearance in dog and man gave longer terminal elimination half-lives (4 6 and 7 6 h respectively). 4. After single i.v. doses of 14C-dofetilide, unchanged drug was the major component excreted in urine of all species with several metabolites also present. 5. Metabolites identified in urine from all species were formed by N-oxidation or N-dealkylation of the tertiary nitrogen atom of dofetilide. 6. After oral and i.v. administration of 14C-dofetilide to man, parent compound was the only detectable component present in plasma and represented 75% of plasma radioactivity. No single metabolite accounted for >5% of plasma radioactivity.