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*IM, intramuscular injection; IV, intravenous administration; qd, once a day; bid, twice a day; tid, three times a day; qid, four times a day.

*The therapeutic uses are identified as examples to emphasize that most benzodiazepines can be used interchangeably. In general, the therapeutic uses of a given benzodiazepine are related to its half-life and may not match the marketed indications. The issue is addressed more extensively in the text.

^Half-life of active metabolite may differ. See Appendix II in the 11th edition of the parent text for additional information.

'For additional dosage information, see Chapter 13 (Anesthesia), Chapter 17 (Anxiety), and Chapter 19 (Seizure Disorders).

^Approved as a sedative-hypnotic only for management of alcohol withdrawal; doses in a nontolerant individual would be smaller.

#Recommended doses vary considerably depending on specific use, condition of patient, and concomitant administration of other drugs.

*IM, intramuscular injection; IV, intravenous administration; qd, once a day; bid, twice a day; tid, three times a day; qid, four times a day.

*The therapeutic uses are identified as examples to emphasize that most benzodiazepines can be used interchangeably. In general, the therapeutic uses of a given benzodiazepine are related to its half-life and may not match the marketed indications. The issue is addressed more extensively in the text.

^Half-life of active metabolite may differ. See Appendix II in the 11th edition of the parent text for additional information.

'For additional dosage information, see Chapter 13 (Anesthesia), Chapter 17 (Anxiety), and Chapter 19 (Seizure Disorders).

^Approved as a sedative-hypnotic only for management of alcohol withdrawal; doses in a nontolerant individual would be smaller.

#Recommended doses vary considerably depending on specific use, condition of patient, and concomitant administration of other drugs.

although this carries the drawback of increased abuse liability and severity of withdrawal after drug discontinuation. Antianxiety agents should have a long t1/2 despite the risk of neuropsychological deficits caused by drug accumulation.

UNTOWARD EFFECTS At the time of peak concentration in plasma, hypnotic doses of benzodiazepines cause varying degrees of lightheadedness, lassitude, increased reaction time, motor incoordination, impairment of mental and motor functions, confusion, and anterograde amnesia. Cognition appears to be affected less than motor performance. All these effects can greatly impair driving and other psychomotor skills, especially if combined with ethanol. These dose-related residual effects can be insidious because most subjects underestimate the degree of their impairment. Residual daytime sleepiness also may occur. The intensity and incidence of CNS toxicity generally increase with age.

Other relatively common side effects are weakness, headache, blurred vision, vertigo, nausea and vomiting, epigastric distress, and diarrhea; joint pains, chest pains, and incontinence are much rarer. Anticonvulsant benzodiazepines sometimes actually increase the frequency of seizures in patients with epilepsy. Possible adverse effects of altered sleep patterns are discussed below.

Adverse Psychological Effects

Benzodiazepines may cause paradoxical effects. Flurazepam occasionally increases the incidence of nightmares—especially during the first week of use—and sometimes causes garrulousness, anxiety, irritability, tachycardia, and sweating. Amnesia, euphoria, restlessness, hallucinations, and hypomanic behavior have been reported to occur during use of various benzodiazepines. The release of bizarre uninhibited behavior occurs in some users; hostility and rage may occur in others; these are referred to as disinhibition or dyscontrol reactions. Paranoia, depression, and suicidal ideation also occasionally may accompany the use of these agents. Such paradoxical or disinhibition reactions are rare and appear to be dose-related. Because of reports of an increased incidence of confusion and abnormal behaviors, triazolam has been banned in the U.K., although the FDA declared triazolam to be safe and effective in low doses of0.125-0.25 mg. Surveys in the U.K. after the ban found that patients did not have fewer side effects with replacement treatments.

Chronic benzodiazepine use poses a risk for development of dependence and abuse, but not to the same extent as seen with older sedatives and other recognized drugs of abuse. Mild dependence may develop in many patients who have taken therapeutic doses of benzodiazepines on a regular basis for prolonged periods. Withdrawal symptoms may include temporary intensification of the problems that originally prompted their use (e.g., insomnia or anxiety). Dysphoria, irritability, sweating, unpleasant dreams, tremors, anorexia, and faintness or dizziness also may occur, especially when withdrawal of the benzodiazepine occurs abruptly; it is prudent to taper the dosage gradually to discontinue therapy. Nonetheless, benzodiazepines are relatively safe drugs. Even huge doses are rarely fatal unless other drugs are taken concomitantly, and true coma is uncommon in the absence of another CNS depressant (e.g., ethanol). Although overdosage with a benzodiazepine rarely causes severe cardiovascular or respiratory depression, therapeutic doses can further compromise respiration in patients with COPD or OSA. Abuse of benzodiazepines includes the use of flunitrazepam (rohypnol) as a "date-rape" drug.

Adverse Effects and Drug Interactions

A variety of allergic, hepatotoxic, and hematologic reactions to the benzodiazepines may occur, but the incidence is quite low; these reactions have been associated with the use of flurazepam and triazolam but not with temazepam. Large doses taken just before or during labor may cause hypothermia, hypotonia, and mild respiratory depression in the neonate. Abuse by the pregnant mother can result in a withdrawal syndrome in the newborn.

Except for additive effects with other sedative or hypnotic drugs, reports of clinically important pharmacodynamic interactions between benzodiazepines and other drugs have been infrequent. Ethanol increases both the rate of absorption of benzodiazepines and the associated CNS depression. Valproate and benzodiazepines in combination may cause psychotic episodes.

Novel Benzodiazepine-Receptor Agonists: Zolpidem and Zalephon

Hypnotics that are structurally dissimilar to benzodiazepines include zolpicone (not available in the U.S.), zolpidem (ambient), zaleplon (sonata), and indiplon (under review by the FDA); presumably, their therapeutic efficacies are due to agonist effects at the benzodiazepine site of the GABAA receptor.

Zaleplon and zolpidem are effective in relieving sleep-onset insomnia. The two drugs have similar efficacies and both display sustained hypnotic efficacy without occurrence of rebound insomnia on abrupt discontinuation. Late-night administration of Zolpidem has been associated with morning sedation, delayed reaction time, and anterograde amnesia, whereas zaleplon has no more side effects than placebo. Tolerance to zaleplon does not appear to occur, nor do rebound insomnia or withdrawal symptoms after stopping treatment. Unlike the benzodiazepines, Zolpidem has little effect on the stages of sleep in normal human subjects. The drug is as effective as benzodiazepines in shortening sleep latency and prolonging total sleep time in patients with insomnia. After discontinuation of zolpidem, the beneficial effects on sleep reportedly persist for up to 1 week, but mild rebound insomnia on the first night also has occurred. Tolerance and physical dependence develop only rarely. An extended-release formulation of zolpidem (ambien cr) is now marketed in the U.S.

Flumazenil: A Benzodiazepine-Receptor Antagonist

Flumazenil (romazicon) is an imidazobenzodiazepine that behaves as a specific benzodiazepine antagonist. Flumazenil binds with high affinity to specific sites on the GABAa receptor, where it competitively antagonizes the binding and allosteric effects of benzodiazepines and other ligands. The drug antagonizes both the electrophysiological and behavioral effects of agonist and inverse-agonist benzodiazepines and [3-carbolines. Anticonvulsant effects cannot be relied on for therapeutic utility because the administration of flumazenil may precipitate seizures under certain circumstances (see below).

Flumazenil is available only for intravenous administration. Although absorbed rapidly after oral administration, <25% of the drug reaches the systemic circulation owing to extensive firstpass hepatic metabolism; effective oral doses are apt to cause headache and dizziness. On intravenous administration, flumazenil is eliminated almost entirely by hepatic metabolism to inactive products with a t1/2 of about 1 hour; the duration of clinical effects usually is only 30-60 minutes.

The primary uses of flumazenil are the management of suspected benzodiazepine overdose and the reversal of sedative effects produced by benzodiazepines administered during either general anesthesia or diagnostic and/or therapeutic procedures.

The administration of a series of small injections is preferred to a single bolus injection. A total of 1 mg flumazenil given over 1-3 minutes usually is sufficient to abolish the effects of therapeutic doses of benzodiazepines; patients with suspected benzodiazepine overdose should respond adequately to a cumulative dose of 1-5 mg given over 2-10 minutes; a lack of response to 5-mg flumazenil strongly suggests that a benzodiazepine is not the major cause of sedation. Additional courses of treatment with flumazenil may be needed within 20-30 minutes should sedation reappear. Flumazenil is not effective in single-drug overdoses with either barbiturates or tri-cyclic antidepressants. To the contrary, administration of flumazenil in these settings may be associated with the onset of seizures, especially in patients poisoned with tricyclic antidepres-sants. Seizures or other withdrawal symptoms also may be precipitated in patients who had been taking benzodiazepines for protracted periods and in whom tolerance and/or dependence may have developed.

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