Pharmacokinetics of single oral and multiple intravenous and oral administration of acebutolol enantiomers in a rat model.

Acebutolol (AC), is a chiral, beta-adrenergic blocking agent which possesses partial agonist activity and is metabolized to an equipotent chiral metabolite, diacetolol (DC). The enantiomeric disposition of AC is reported following racemic administration as a single oral (p.o., 50 mg kg(-1)) or as a multiple thrice daily intravenous (i.v.) or p.o. dosing for four days in male Sprague-Dawley rats (n = 6). Enantiomeric concentrations of AC and DC in plasma and urine were determined using a stereospecific HPLC assay. The bioavailabilities of R- and S-enantiomer were 0.40 and 0.39 after single dose administration of AC respectively. These values were increased to 0.51 and 0.53 after multiple dosing. Although no significant differences were found in AUC0-infinity after single i.v. as compared with AUC0-tau after multiple i.v. dosing of AC, the 39 and 45% increase in mean AUC0-tau were found after multiple p.o. dosing over the corresponding AUC0-infinity, for the single p.o. dose of AC for R- and S-enantiomer, respectively. The disposition of DC as well as the urinary excretion of metabolite was stereoselective in favor of R-enantiomer after oral administration of AC. These results indicate that AC enantiomers have low availability and moderate extraction through the first-pass metabolism in a rat model. The higher AUC values after p.o. multiple dosing may suggest a saturable first-pass metabolism of AC.