Abstract
1 Twelve volunteers, of mean age 60 years, took part in a double-blind, balanced cross-over study, to compare effects of chlormezanone 400 mg and nitrazepam 5 mg on electrophysiologically-recorded and subjectively-rated sleep. 2 In the first week of administration nitrazepam caused a significant shortening of the time to fall asleep, but following withdrawal subjects took longer to fall asleep than during the baseline period. 3 Both chlormezanone and nitrazepam initially caused increase of sleep duration and less interruption of sleep by wakefulness. By the third week, for chlormezanone this effect was no longer significant, and for nitrazepam there was a significant decline in the effect. There was no statistically significant difference between the two drugs for these measures. 4 The drugs differed little in their effects on the amount of the various sleep stages, except that nitrazepam significantly reduced the duration of slow wave sleep, whereas chlormezanone had no significant effect on slow wave sleep. Both drugs reduced the amount of REM sleep in the first 6 h of sleep but only nitrazepam reduced the percentage of the time spent in REM sleep of the whole night. 5 Subjects' own ratings of sleep quality showed that both of the drugs improved sleep, but following withdrawal it was only after nitrazepam that there was impairment of the quality of sleep. Neither drug affected subjective alertness in the morning.