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Mechanism of Action
Quazepam, like other central nervous system agents of the 1,4-benzodiazepine class, presumably exerts its effects by binding to stereo-specific receptors at several sites within the central nervous system (CNS). The exact mechanism of action is unknown.
Quazepam is rapidly (absorption half-life of about 30 minutes) and well absorbed from the gastrointestinal tract. The peak plasma concentration of quazepam is approximately 20 ng/mL after a 15 mg dose and occurs at about 2 hours.
Quazepam, the active parent compound, is extensively metabolized in the liver; two of the plasma metabolites are 2-oxoquazepam and N-desalkyl-2-oxoquazepam. All three compounds show CNS depressant activity.
The degree of plasma protein binding for quazepam and its two major metabolites is greater than 95%.
Following administration of 14C-quazepam, 31% of the dose appeared in the urine and 23% in the feces over five days; only trace amounts of unchanged drug were present in the urine.
The mean elimination half-life of quazepam and 2-oxoquazepam is 39 hours and that of Ndesalkyl-2-oxoquazepam is 73 hours. Steady-state levels of quazepam and 2-oxoquazepam are attained by the seventh daily dose and that of N-desalkyl-2-oxoquazepam by the thirteenth daily dose.
Geriatrics: The pharmacokinetics of quazepam and 2-oxoquazepam in geriatric subjects are comparable to those seen in young adults; as with desalkyl metabolites of other benzodiazepines, the elimination half-life of N-desalkyl-2-oxoquazepam in geriatric patients is about twice that of young adults.
Bupropion (a CYP2B6 substrate): Co-administration of a single dose of 150 mg Bupropion Hydrochloride XL with steady state quazepam did not significantly affect the AUC and Cmax of bupropion or its primary metabolite, hydroxybupropion.
The effectiveness of DORAL was established in placebo-controlled clinical studies of 5 nights duration in acute and chronic insomnia. The sustained effectiveness of DORAL was established in chronic insomnia in a sleep laboratory (polysomnographic) study of 28 nights duration.
In the sleep laboratory study, DORAL significantly decreased sleep latency and total wake time, and significantly increased total sleep time and percent sleep time, for one or more nights. Doral 15 mg was effective on the first night of administration. Sleep latency, total wake time and wake time after sleep onset were still decreased and percent sleep time was still increased for several nights after the drug was discontinued. Percent slow wave sleep was decreased, and REM sleep was essentially unchanged. No transient sleep disturbance, such as “rebound insomnia,” was observed after withdrawal of the drug in sleep laboratory studies in 12 patients using 15 mg doses.
In outpatient studies, DORAL Tablets improved all subjective measures of sleep including sleep latency, duration of sleep, number of awakenings, occurrence of early morning awakening, and sleep quality. Some effects were evident on the first night of administration of DORAL (sleep latency, number of awakenings, and duration of sleep).
A double-blind, controlled sleep laboratory study (N=30) in elderly patients compared the effects of quazepam 7.5 mg and 15 mg to that of placebo over a period of 7 days. Both the 7.5 mg and 15 mg doses appeared to be effective. Caution must be used in interpreting this data due to the small size of the study.
Last reviewed on RxList: 5/28/2013
This monograph has been modified to include the generic and brand name in many instances.
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