Conventional and Power Spectrum Analysis of the Effects of Zolpidem on Sleep EEG in Patients with Chronic Primary Insomnia

STUDY OBJECTIVE: The purpose of this study was 1) to assess the effect of zolpidem or a placebo on sleep in two groups of insomniac patients with a diagnosis of moderate-to-severe chronic primary insomnia and 2) to determine the effect of zolpidem on sleep structure using spectral analysis. DESIGN: A randomized, double-blind, placebo-controlled trial. SETTING: Sleep laboratory of the Department of Pharmacology and Therapeutics at the Clinics Hospital. PARTICIPANTS: 12 female outpatients with chronic primary insomnia. INTERVENTIONS: Zolpidem was given at a daily dose of 10 mg for 15 nights. RESULTS: The hypnotic drug reduced sleep latency and waking time after sleep onset, and increased total sleep time and sleep efficiency. Values corresponding to visually scored slow wave sleep (stage 3 and 4) showed no significant changes. All-night spectral analysis of the EEG revealed that power density in NREM sleep was significantly increased in the low frequency band (0.25-1.0 Hz) in the zolpidem group during the first 2-h interval. CONCLUSIONS: In agreement with previous findings obtained in patients with chronic primary insomnia, zolpidem significantly improved sleep induction and maintenance. Moreover, zolpidem increased power density in the 0.25-1.0 Hz band during short-term and intermediate-term treatment. Nevertheless, other frequency bands in the delta range showed a relative decrease which was not statistically significant.