benzodiazepine — ベンゾジアゼピン
One of a group of structurally related drugs used mainly as sedatives/hypnotics, muscle relaxants, and anti-epileptics, and once referred to by the now-deprecated term “minor tranquillisers”. These agents are believed to produce therapeutic effects by potentiating the action of gamma-aminobutyric acid (GABA), a major inhibitory neurotransmitter.
Benzodiazepines were introduced as safer alternatives to barbiturates. They do not suppress REM sleep to the same extent as barbiturates, but have a significant potential for physical and psychological dependence and misuse.
Short-acting benzodiazepines include halazepam and triazolam, both with rapid onset of action; alprazolam, flunitrazepam, nitrazepam, lorazepam, and temazepam, with intermediate onset; and oxazepam, with slow onset. Profound anterograde amnesia (“blackout”) and paranoia have been reported with triazolam, as well as rebound insomnia and anxiety. Many clinicians have encountered particularly difficult problems on discontinuing treatment with alprazolam.
Long-acting benzodiazepines include diazepam (with the fastest onset of action), clorazepate (also fast onset), chlordiazepoxide (intermediate onset), flurazepam (slow onset), and prazepam (slowest onset). The long-acting benzo-diazepines may produce a cumulative disabling effect and are more likely than the short-acting agents to cause daytime sedation and motor impairment.
Even when benzodiazepines are taken in therapeutic doses, their abrupt discontinuation induces a withdrawal syndrome in up to 50% of people treated for 6 months or longer. Symptoms are more intense with shorteracting preparations; with the long-acting benzodiazepines, withdrawal symptoms appear one or two weeks after discontinuation and last longer, but are less intense. As with other sedatives, a schedule of slow detoxification is necessary to avoid serious complications such as withdrawal seizures.
Some benzodiazepines have been used in combination with other psychoactive substances to accentuate euphoria, e.g. 40-80 mg of diazepam taken shortly before or immediately after a daily maintenance dose of methadone. Benzodiazepines are frequently misused in conjunction with alcohol or in opioid dependence (see multiple drug use).
Fatal overdose is rare with any benzodiazepine unless it is taken concurrently with alcohol or other central nervous system depressants.