“…Thus, the doses of zopiclone, triazolam, and nitrazepam we used are thought to be equivalent to 20 Tada/Sato/Sakai/Ueda/Kasamo/Kojima Effects of Hypnotics on Standing Steadiness Previous investigators have reported weak musclerelaxant effects of zopiclone as compared to classical ben zodiazepines in mice, rats, and cats. For instance, the muscle-relaxant effects of zopiclone were approximately 4-80 times less potent than those of nitrazepam in mice and rats [15,16], and 3.5-5 times less potent than those of diazepam in mice, rats, or cats [1], However, the present preliminary data indicating stronger muscle-relaxant ac tivities of zopiclone than of nitrazepam in humans do not support these previous animal experiments. Pharmacoki netic differences between zopiclone and nitrazepam do not seem to explain the differences between studies since our previous pharmacokinetic-dynamic study of nitraze pam indicated that peak effects of nitrazepam were ob tained at 1 and 2 h after drug administration [6,17], Thus, there seem to be great species differences in terms of muscle-relaxant effects of zopiclone.…”