Stereoselective pharmacokinetics of propafenone and its major metabolites in healthy Chinese volunteers.

The stereoselective pharmacokinetics of propafenone (PPF) and its active metabolite 5-hydroxypropafenone (5-OHP) as well as their glucuronide and sulfate conjugates have been investigated, in order to clarify the relationship between metabolism and stereoselective disposition of PPF in humans. After oral administration of 300 mg racemic PPF hydrochloride to 10 healthy Chinese subjects, the areas under the plasma concentration-time curves (AUCs) for (S)-PPF were significantly higher (S/R ratio, 1.50+/-0.17) and the apparent oral clearance significantly lower (S/R ratio, 0.68+/-0.07) than those parameters for (R)-PPF. In contrast, the AUCs of PPF glucuronide (PPF-G) were lower for (S)-PPF-G than for the (R)-enantiomer (S/R ratio, 0.83+/-0.12). The partial clearance of (S)-PPF by glucuronidation pathway was lower than that of (R)-PPF and the enantiomeric ratio was 0.62+/-0.04. The t(max) values of PPF glucuronide diastereoisomers showed no statistically significant differences between each other, but were much shorter than the corresponding values of the parent drug, implying that glucuronidation may be the 'first-choice' pathway in presystemic metabolism of PPF. Glucuronidation of 5-OHP favored the (S)-enantiomer, whereas the sulfation showed a large preference for the (R)-enantiomer. After beta-glucuronidase hydrolysis, no significant differences were observed in AUCs between 5-OHP enantiomers (including unconjugated and conjugated 5-OHP). The results suggest that the significant difference in disposition between PPF enantiomers may be, at least in part attributed to stereoselective metabolism in the glucuronidation pathway.