Clinical pharmacokinetics of zopiclone

Zopiclone is a cyclopyrrolone hypnotic agent. It possesses a chiral centre and is commercially available as a racemic mixture. Methods involving high performance liquid chromatography (HPLC), gas chromatography, capillary electrophoresis (CE) and high performance thin layer chromatography have been developed for the quantitation of zopiclone and its 2 main metabolites in biological samples. For the chiral determination of the enantiomers of zopiclone and its metabolites, HPLC and CE methods are available. After oral administration, zopiclone is rapidly absorbed, with a bioavailability of approximately 80%. The plasma protein binding of zopiclone has been reported to be between 45 and 80%. Zopiclone is rapidly and widely distributed to body tissues including the brain, and is excreted in urine, saliva and breast milk. Zopiclone is partly metabolised in the liver to form an inactive N-demethylated derivative and an active N-oxide metabolite. In addition, approximately 50% of the administered dose is decarboxylated and excreted via the lungs. Less than 7% of the administered dose is renally excreted as unchanged zopiclone. In urine, the N-demethyl and N-oxide metabolites account for 30% of the initial dose. The terminal elimination half-life (t1/2z) of zopiclone ranges from 3.5 to 6.5 hours. The pharmacokinetics of zopiclone in humans are stereoselective. After oral administration of the racemic mixture, Cmax (time to maximum plasma concentration), AUC (area under the plasma time-concentration curve) and t1/2z values are higher for the dextrorotatory enantiomer owing to the slower total clearance and smaller volume of distribution (corrected by the bioavailability), compared with the levorotatory enantiomer. In urine, the concentrations of the dextrorotatory enantiomers of the N-demethyl and N-oxide metabolites are higher than those of the respective antipodes. The pharmacokinetics of zopiclone are altered by aging and are influenced by renal and hepatic functions. Drug interactions have been observed with erythromycin, trimipramine and carbamazepine.