Zopiclone. A review of its pharmacological properties and therapeutic efficacy as an hypnotic.

Zopiclone is a cyclopyrrolone which is chemically unrelated to the benzodiazepines and is thought to act on the GABAA receptor complex at a site distinct from, but closely related to, the benzodiazepine binding site. The hypnotic efficacy of zopiclone administered as single oral doses has been demonstrated in patients undergoing next-day surgery and in patients with insomnia, and these studies have established an optimal dose of 7.5mg for elderly patients. Using this dose, clinical studies have shown that zopiclone improved sleep in elderly patients to a similar extent as triazolam 0.125 to 0.5mg, flurazepam 15mg, and nitrazepam 5mg. Studies that also included younger patients have shown that zopiclone 7.5mg is at least as effective as triazolam 0.25 or 0.5mg, and on most sleep parameters is comparable to temazepam 20mg, nitrazepam 5mg, flunitrazepam 2mg, and flurazepam 20mg. Zopiclone causes minimal impairment to psychomotor performance and mental alertness the morning after night-time administration. The drug is generally well tolerated by patients of all ages; the most frequently reported adverse effects being bitter taste and dry mouth. Treatment withdrawal due to adverse effects is seldom required and reports of rebound insomnia after zopiclone withdrawal are rare. While symptoms of physical dependence have not been observed in clinical studies, there have been isolated reports of physical dependence in patients with a history of substance abuse. Although the latter finding should be kept in mind, it appears that zopiclone has a low dependence liability. Thus, with its short duration of action and good tolerability profile, zopiclone is a well established alternative to the benzodiazepine hypnotics and may be particularly beneficial in those patients unable or unwilling to tolerate the residual effects associated with many other hypnotic agents.