Interactions and comparative effects of zopiclone, diazepam and lorazepam on psychomotor performance and on elimination pharmacokinetics in healthy volunteers.

A randomised, placebo-controlled, double blind single-dose cross-over study was arranged to investigate possible interactions between zopiclone (7.5 mg) and two widely used benzodiazepine (BZD) anxiolytics diazepam (5 mg) and lorazepam (1 mg) during the elimination phase of drugs. Psychomotor performance was tested before and 1, 6, 8, 12 and 24 hr after the drug administration. Simultaneously, blood samples were drawn for determination of plasma drug concentrations. The elimination of each compound was not altered by coadministration of other drugs. As expected, one hour after drug ingestion, psychomotor performance was impaired. The coadministration of drugs increased the effect. During the elimination phase, 6 and 8 hr after the drug intake, only zopiclone and lorazepam in combination slightly impaired performance as compared with the pretreatment levels, but there was no difference as compared with placebo. Adverse events after active treatments were not significantly different from those after placebo. At the recommended dose of 7.5 mg, zopiclone does not alter the elimination pharmacokinetics of the BZD anxiolytics diazepam (5mg) and lorazepam (1 mg), and neither is the elimination of zopiclone affected by these BZDs. Due to the rapid elimination of zopiclone, the increase in sedation seen after concurrent administration with BZDs is of short duration.