Eszopiclone is the S-isomer of racemic zopiclone, a cyclopyrrolone with sedative-hypnotic activity that has been available in Europe, Canada, and Latin America since 1987. Eszopiclone acts by binding to the GABAA receptor. In contrast to the benzodiazepine (BZD) hypnotics, eszopiclone has more selectivity for certain subunits of the GABAA receptor. Oral eszopiclone is rapidly absorbed and extensively distributed to body tissues including the brain. Peak plasma concentrations are attained 1.0–1.6 hours after a 3 mg dose, while the mean elimination half-life is 6 hours. The half-life increases with age to about 9.0 hours in patients 65 years or older. Eszopiclone’s pharmacokinetic (PK) profile is not substantially modified in patients suffering from renal failure or mild-to-moderate hepatic impairment, although patients with severe hepatic insufficiency should have a reduced dose. The subjective perception of improved sleep following eszopiclone 2 or 3 mg treatment has been demonstrated in randomized, double-blind, placebo-controlled studies of up to 6 months’ duration. In these studies the drug significantly reduced sleep onset latency (SOL), the number of awakenings, and wake time after sleep onset (WASO) whereas total sleep time (TST) and quality of sleep were increased in non-elderly and elderly subjects. Sleep laboratory studies of the effects of eszopiclone have confirmed the drug’s clinical efficacy in subjects with chronic primary insomnia. Eszopiclone, unlike BZD hypnotics, does not significantly alter values corresponding to slow wave sleep (SWS or stages 3 and 4) and rapid eye movement (REM) sleep. Rebound insomnia following withdrawal of eszopiclone has been examined in only one study. Discontinuation of the active treatment with 2 mg was followed by rebound insomnia in non-elderly subjects. Three-mg doses of eszopiclone administered for a period of up to 12 months was associated with a sustained beneficial effect on sleep induction and maintenance, with no occurrence of tolerance. The most common side-effects were unpleasant or bitter taste, headache, dyspepsia, pain, diarrhea, dry mouth, upper respiratory infection, urinary tract infection, dizziness, and accidental injury. New adverse events (withdrawal symptoms) including anxiety, abnormal dreams, hyperesthesia, nausea, and upset stomach were recorded in one study on the days following eszopiclone 2 or 3 mg discontinuation. Although dependence and abuse potential have not been formally assessed, unpublished data show that eszopiclone at doses of 6 and 12 mg produces euphoria effects similar to those of diazepam 20 mg in BZD drug addicts. In conclusion, available evidence tends to indicate that eszopiclone is effective and safe for the treatment of chronic primary insomnia in non-elderly and elderly subjects. Tolerance did not occur during active drug administration for a 12-month period. Thus eszopiclone can be efficacious not only during short- and intermediate-term administration but also in patients requiring prolonged regular drug usage
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