Biotransformation and pharmacokinetic overview of enoximone and its sulfoxide metabolite

Enoximone possesses both positive inotropic and vasodilatory activities and may be useful in the treatment of patients with congestive heart failure (CHF). In all animal species investigated (rat, dog, monkey and man), the major urinary metabolite is the sulfide oxidation product (sulfoxide); very little unchanged drug appears in urine. Both in vitro and in vivo animal studies indicate reversibility of the sulfoxidation reaction; therefore, it is presumed that sulfoxidation is reversible in man. In normal healthy subjects, no difference in extent of absorption due to dietary state is observed. In patients with New York Heart Association class III to IV CHF, median terminal disposition half-lives for enoximone and its sulfoxide metabolite are 6.2 to 7.6 hours, respectively. Enoximone and sulfoxide plasma concentrations from high dose intravenous infusion studies in patients with class III to IV CHF were also investigated. The collective data suggest nonlinearity in one or more pharmacokinetic processes, of which one may be saturation of sulfoxidation. No direct relation between enoximone and/or the sulfoxide metabolite plasma concentration and pharmacologic effect has been established.