The effects of zolpidem and zopiclone on daytime sleepiness and psychomotor performance

Zolpidem (ZLP), which has selective affinity to the BZ1 (omega 1) receptor and a short half-life, is a novel hypnotic. The objective of this study is to compare the residual effects of standard clinical doses of ZLP and zopiclone (ZPC), a short-acting hypnotic marginally selective for the BZ1 (omega 1) receptor, given in a single dose on daytime sleepiness and psychomotor function. This study was carried out as a double-blind cross-over study with 10 mg ZLP, 7.5 mg ZPC and a placebo in 12 healthy male adults. In the multiple sleep latency test, sleep latency was not reduced but increased by ZLP and ZPC as well as the placebo when drug plasma levels had nearly reached the peak. Subjects administered ZLP were significantly more feeble, lethargic and antagonistic in mood rating scales than those administered ZPC. The incidence of severe behavioral side effects was higher in the case of ZLP than in the case of ZPC over the same period. Sleep latency the next morning was significantly shorter in the case of ZPC than in the case of ZLP or the placebo. The tapping test performed at the same time demonstrated that the number of taps was significantly less in the case of ZPC than in the case of ZLP or the placebo. The results of the present study suggest that ZLP acts more rapidly than ZPC. On the other hand, ZLP has less residual effect on sleepiness and psychomotor function the next morning.