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Pharmacology & Pharmacokinetics
Zolpidem, an imidazopyridine, is structurally unrelated to other hypnotics. It binds preferentially to one of the benzodiazepine receptor subtypes (omega-1; benzodiazepine-1). 1 Benzodiazepines bind to all three subtypes and zopiclone to two.
Zolpidem is rapidly absorbed after being swallowed, onset of action is within 30 minutes, 2 and the drug is effective for up to 6 hours. Peak plasma concentrations occur between 0.5 and 3 hours, and the elimination half-life is about 2 hours. Zolpidem is metabolised by the liver and its inactive metabolites are excreted in the urine and faeces. In older patients and those with hepatic impairment plasma concentrations are increased.
Clinical studies
Zolpidem has been compared with the benzodiazepines flunitrazepam (half-life about 20 hours) and triazolam (half- life about 3 hours; not available in the UK) in studies in healthy volunteers and patients with insomnia. No studies have been published comparing it with the short acting hypnotics temazepam or zopiclone.
Comparisons with placebo
In a controlled, crossover study 30 elderly volunteers (aged 60-79 years) were randomised to either zolpidem 5mg, 15mg or placebo or zolpidem 10mg, 20mg or placebo. At all doses zolpidem reduced the time taken to fall asleep; the effects were dose dependent. 2 In a double-blind, controlled study of 75 patients (aged 21-60 years) with chronic insomnia, zolpidem (10mg and 15mg) taken 30 minutes before bedtime for 35 consecutive nights reduced time taken to fall asleep by 15-30 minutes and increased total time asleep by 25-40 minutes. 3
Comparisons with benzodiazepines
In a 3-week double-blind study involving 205 inpatients with insomnia (aged 58-98 years), zolpidem (5mg and 10mg) and triazolam (0.25mg) were equally effective in improving the quality of sleep assessed by the patient using a questionnaire and visual analogue scale. The effect on total sleep time varied, increasing by approximately 1.5 hours with 5mg zolpidem and by 2 hours with 10mg zolpidem or 0.25mg triazolam. 4 In a 3-night general practice study in 18 women complaining of insomnia zolpidem (10mg) was as effective as flunitrazepam (2mg) in reducing the time to fall asleep, but only flunitrazepam increased time asleep. 5 In further studies zolpidem, in a high dose of 20mg, was as effective as triazolam (0.5mg) 6 or flunitrazepam (2mg). 7
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