OBJECTIVE: This paper reviews the pharmacologic and pharmacokinetic properties, clinical efficacy, and safety profile of the nonbenzodiazepine cyclopyrrolone agent eszopiclone in the management of adult patients with insomnia. METHODS: Recent studies, abstracts, reviews, and consensus statements published in English were identified through searches of MEDLINE (1966-December 2005), International Pharmaceutical Abstracts (1970 December 2005), and PharmaProjects (1990-December 2005) using the search terms eszopiclone, cyclopyrrolone, insomnia, nonbenzodiazepine, and zopiclone enantiomer. Selected information provided by the manufacturer of eszopiclone was included, as were all pertinent clinical trials. RESULTS: Eszopiclone is rapidly absorbed after oral administration, with Tmax achieved within approximately 1 hour and a terminal-phase elimination half-life of approximately 6 hours. Approximately 52% to 59% of a dose is weakly bound to plasma protein. Eszopiclone is extensively metabolized by oxidation and demethylation. In vitro studies have indicated that the cytochrome P450 (CYP) isozymes CYP3A4 and CYP2E1 are involved in the biotransformation of eszopiclone; therefore, drugs that induce or inhibit these CYP isozymes may affect the metabolism of eszopiclone. Eszopiclone is excreted in the urine as racemic zopiclone at <10% of the orally administered dose. Six Phase III clinical trials were identified that evaluated the safety profile and efficacy of eszopiclone, 1 in healthy subjects with transient insomnia and 5 in patients with primary chronic insomnia (3 in younger adults and 2 in the elderly). In the trials in younger adults, eszopiclone significantly improved sleep efficiency, sleep latency, wake time after sleep onset, number of awakenings, number of nights awakened weekly, total sleep time, and quality and depth of sleep compared with placebo (P<0.05). In the trials in elderly patients, who received eszopiclone 2 mg or placebo for 2 weeks, eszopiclone was associated with significantly shorter sleep latency compared with placebo (P<0.004), as well as a significant decrease in the cumulative number of naps (P<0.05). The most commonly reported drug-related, dose-responsive adverse event in clinical trials of eszopiclone 2 and 3 mg was bitter taste (17% and 34%, respectively), followed by dizziness (5% and 7%) and dry mouth (5% and 7%). Somnolence occurred at an incidence of 4% to 9% with both doses. Tolerance or rebound insomnia was not reported. CONCLUSIONS: Eszopiclone represents an effective and well-tolerated option for the treatment of insomnia. In the absence of published studies comparing eszopiclone with similar hypnotic agents (eg, zolpidem, zaleplon, zopiclone), it is not yet possible to evaluate its efficacy relative to other agents used for insomnia.