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Prosom (Estazolam) - Description and Clinical Pharmacology


(estazolam tablets)


ProSom (estazolam), a triazolobenzodiazepine derivative, is an oral hypnotic agent. Estazolam occurs as a fine, white, odorless powder that is soluble in alcohol and practically insoluble in water. The chemical name for estazolam is 8−chloro−6−phenyl−4H−s−triazolo[4,3-α] [1,4]benzodiazepine. The empirical formula is C16H11ClN4. The structural formula is represented as follows:

ProSom tablets are scored and contain either 1 mg or 2 mg of estazolam.

Inactive Ingredients

Colloidal silicon dioxide, lactose, povidone, stearic acid, and sodium starch glycolate.

In addition, the 2 mg tablets contain FD&C Red No. 40.




ProSom tablets have been found to be equivalent in absorption to an orally administered solution of estazolam. In healthy subjects who received up to three times the recommended dose of ProSom, peak estazolam plasma concentrations occurred within two hours after dosing (range 0.5 to 6.0 hours) and were proportional to the administered dose, suggesting linear pharmacokinetics over the dosage range tested.


Independent of concentration, estazolam in plasma is 93% protein bound.


Estazolam is extensively metabolized. Only two metabolites (1-oxo-estazolam & 4 − hydroxy − estazolam) were detected in human plasma up to 18 hrs.

The pharmacologic activity of estazolam is primarily from the parent drug. The elimination of the parent drug takes place via hepatic metabolism of estazolam to hydroxylated and other metabolites that are eliminated largely in the urine both free and conjugated. In humans, greater than 70% of a single dose of estazolam was recovered in the urine as metabolites. Less than 5% of a 2 mg dose of estazolam was excreted unchanged in the urine, with only 4% of the dose appearing in the feces. The principal urinary excretion product is an unidentified metabolite, presumed to be a metabolic product of 4-hydroxy-estazolam, accounting for at least 27% of the administered dose. 4 − hydroxy-estazolam is the major metabolite in plasma, with concentrations approaching 12% of those of the parent eight hours after administration. Urinary 4 − hydroxy − estazolam and 1-oxo-estazolam account for 11.9% and 4.4% of the dose respectively. In vitro studies with human liver microsomes indicate that the biotransformation of estazolam to the major circulating metabolite 4 − hydroxy − estazolam is mediated by cytochrome P450 3A (CYP3A). While 4-hydroxy-estazolam and the lesser metabolite, 1-oxo-estazolam, have some pharmacologic activity, their low potencies and low concentrations preclude any significant contribution to the hypnotic effect of ProSom.


The range of estimates for the mean elimination half-life of estazolam varied from 10 to 24 hours. Radiolabel mass balance studies indicate that the main route of excretion is via the kidneys. After 5 days, 87% of the administered radioactivity was excreted in human urine. Less than 4% of the dose was excreted unchanged. Eleven metabolites were found in urine. Four metabolites were identified as 1-oxo-estazolam, 4' − hydroxy − estazolam, 4-hydroxy-estazolam, and benzophenone, as free metabolites and glucuronides. The predominant metabolite in urine (17% of the administered dose) has not been identified, but is likely to be a metabolite of 4-hydroxy-estazolam.

Special Populations

In a small study (N=8) using various doses in older subjects (59 to 68 years), peak estazolam concentrations were found to be similar to those observed in younger subjects with a mean elimination half-life of 18.4 hours (range 13.5 to 34.6 hours). The influence of hepatic or renal impairment on the pharmacokinetics of estazolam has not been studied.


The pharmacokinetics of estazolam have not been studied in pediatric patients.


The influence of race on the pharmacokinetics of estazolam has not been studied.


The gender-effect on the pharmacokinetics of estazolam has not been investigated.

Cigarette Smoking

The clearance of benzodiazepines is accelerated in smokers compared to nonsmokers, and there is evidence that this occurs with estazolam. This decrease in half-life, presumably due to enzyme induction by smoking, is consistent with other drugs with similar hepatic clearance characteristics. In all subjects and at all doses, the mean elimination half-life appeared to be independent of the dose.

Drug-Drug Interaction

The metabolism of estazolam to the major circulating metabolite 4-hydroxy-estazolam is catalyzed by CYP3A. While no in vivo drug-drug interaction studies were conducted between estazolam and inhibitors/inducers of CYP3A, compounds that are potent CYP3A inhibitors (such as ketoconazole, itraconazole, nefazodone, fluvoxamine, and erythromycin) would be expected to increase plasma estazolam concentrations and CYP3A inducers (such as carbamazepine, phenytoin, rifampin and barbiturates) would be expected to decrease estazolam concentrations.

Drug Interaction with Fluoxetine

A multiple-dose study was conducted to assess the effect of fluoxetine 20 mg BID on the pharmacokinetics of estazolam 2 mg QHS after seven days. The pharmacokinetics of estazolam (Cmax and AUC) were not affected during multiple-dose fluoxetine, suggesting no clinically significant pharmacokinetic interaction.

The Ability of Estazolam to Induce or Inhibit Human Enzyme Systems

The results from in vitro human liver microsomal studies suggest that at therapeutic concentrations, estazolam has no significant inhibitory effect on the major human cytochrome P450 enzyme activities (i.e., CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A). The ability of estazolam to induce human hepatic enzyme systems has not been determined.


Postulated relationship between elimination rate of benzodiazepine hypnotics and their profile of common untoward effects

The type and duration of hypnotic effects and the profile of unwanted effects during administration of benzodiazepine drugs may be influenced by the biologic half-life of administered drug and any active metabolites formed. If half-lives are long, drug or metabolites may accumulate during periods of nightly administration and may be associated with impairments of cognitive and/or motor performance during waking hours; the possibility of interaction with other psychoactive drugs or alcohol will be increased. In contrast, if half-lives are short, drug and metabolites will be cleared before the next dose is ingested, and carry-over effects related to excessive sedation or CNS depression should be minimal or absent. However, during nightly use for an extended period, pharmacodynamic tolerance or adaptation to some effects of benzodiazepine hypnotics may develop. If the drug has a short elimination half-life, it is possible that a relative deficiency of the drug or its active metabolites (i.e., in relationship to the receptor site) may occur at some point in the interval between each night's use. This sequence of events may account for two clinical findings reported to occur after several weeks of nightly use of rapidly eliminated benzodiazepine hypnotics, namely, increased wakefulness during the last third of the night and increased daytime anxiety in selected patients.


Controlled Trials Supporting Efficacy

In three 7-night, double-blind, parallel-group trials comparing estazolam 1 mg and/or 2 mg with placebo in adult outpatients with chronic insomnia, estazolam 2 mg was consistently superior to placebo in subjective measures of sleep induction (latency) and sleep maintenance (duration, number of awakenings, depth and quality of sleep); estazolam 1 mg was similarly superior to placebo on all measures of sleep maintenance, however, it significantly improved sleep induction in only one of two studies. In a similarly designed trial comparing estazolam 0.5 mg and 1 mg with placebo in geriatric outpatients with chronic insomnia, only the 1 mg estazolam dose was consistently superior to placebo in sleep induction (latency) and in only one measure of sleep maintenance (i.e., duration of sleep).

In a single-night, double-blind, parallel-group trial comparing estazolam 2 mg and placebo in patients admitted for elective surgery and requiring sleep medications, estazolam was superior to placebo in subjective measures of sleep induction and maintenance.

In a 12-week, double-blind, parallel-group trial including a comparison of estazolam 2 mg and placebo in adult outpatients with chronic insomnia, estazolam was superior to placebo in subjective measures of sleep induction (latency) and maintenance (duration, number of awakenings, total wake time during sleep) at Week 2, but produced consistent improvement over 12 weeks only for sleep duration and total wake time during sleep. Following withdrawal at Week 12, rebound insomnia was seen at the first withdrawal week, but there was no difference between drug and placebo by the second withdrawal week in all parameters except latency, for which normalization did not occur until the fourth withdrawal week.

Adult outpatients with chronic insomnia were evaluated in a sleep laboratory trial comparing four doses of estazolam (0.25, 0.50, 1.0 and 2.0 mg) and placebo, each administered for 2 nights in a crossover design. The higher estazolam doses were superior to placebo in most EEG measures of sleep induction and maintenance, especially at the 2 mg dose, but only for sleep duration in subjective measures of sleep.

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