二钾氯氮Clorazepate Dipotassium（氯卓酸钾）

Clorazepate, sold under the brand names Tranxene among others, is a benzodiazepine medication. It possesses anxiolytic, anticonvulsant, sedative, hypnotic, and skeletal muscle relaxant properties. Clorazepate is an unusually long-lasting benzodiazepine and serves as a majoritive prodrug for the equally long-lasting desmethyldiazepam, which is rapidly produced as an active metabolite. Desmethyldiazepam is responsible for most of the therapeutic effects of clorazepate.[1]

 

It was patented in 1965 and approved for medical use in 1967.[2]

 

Medical uses

 

Clorazepate is used in the treatment of anxiety disorders and insomnia. It may also be prescribed as an anticonvulsant or muscle relaxant.[3] It is also used as a premedication.[4]

Clorazepate is prescribed principally in the treatment of alcohol withdrawal and epilepsy, although it is also a useful anxiolytic because of its long half-life. The normal starting dosage range of Clorazepate is 15 to 60 mg per day. The drug is to be taken two to four times per day. Dosages as high as 90 to 120 mg per day may be used in the treatment of acute alcohol withdrawal. In the United States and Canada, Clorazepate is available in 3.75, 7.5, and 15 mg capsules or tablets. In Europe, tablet formations are 5 mg, 10 mg, 20 mg and 50 mg.[5] Clorazepate SD (controlled release) is available and may have a reduced incidence of adverse effects. The sustained-release formulation of clorazepate has some advantages in that, if a dose is missed, less profound fluctuations in blood plasma levels occur, which may be helpful to some people with epilepsy at risk of break-through seizures.[6]

 

Contraindications

 

Benzodiazepines require special precaution if used in the elderly, children, alcohol- or drug-dependent individuals and individuals with comorbid psychiatric disorders.[9]

 

Chlorazepate if used late in pregnancy, the third trimester, causes a definite risk a severe benzodiazepine withdrawal syndrome in the neonate with symptoms including hypotonia, and reluctance to suck, to apnoeicspells, cyanosis, and impaired metabolic responses to cold stress. Floppy infant syndrome and sedation in the newborn may also occur. Symptoms of floppy infant syndrome and the neonatal benzodiazepine withdrawal syndrome have been reported to persist from hours to months after birth.[10]

 

Special precaution is required when using clorazepate in the elderly because the elderly metabolise clorazepate more slowly, which may result in excessive drug accumulation. Additionally the elderly are more sensitive to the adverse effects of benzodiazepines compared to younger individuals even when blood plasma levels are the same. Use of benzodiazepines in the elderly is only recommended for 2 weeks and it is also recommended that half of the usual daily dose is prescribed.[6]

 

Adverse effects

 

Adverse effects of clorazepate include, tolerance, dependence, withdrawal reactions, cognitive impairment, confusion, anterograde amnesia, falls in the elderly, ataxia, hangover effects, and drowsiness. It is unclear whether cognitive deficits resulting from the long-term use of benzodiazepines return to normal or persist indefinitely after withdrawal from benzodiazepines. Benzodiazepines are also known to cause or worsen depression. Paradoxical effects including excitement and paradoxical worsening of seizures can sometimes result from the use of benzodiazepines. Children, the elderly, individuals with a history of alcohol abuse or a history of aggressive behavior and anger are at greater risk of developing paradoxical reactions to benzodiazepines.[6]

 

Tolerance, dependence and withdrawal

 

Delirium has been noted from discontinuation from clorazepate[7] A benzodiazepine dependence occurs in approximately one third of patients who take benzodiazepines for longer than 4 weeks, which is characterised by a withdrawal syndrome upon dose reduction. When used for seizure control, tolerance may manifest itself with an increased rate of seizures as well an increased risk of withdrawal seizures. In humans, tolerance to the anticonvulsant effects of clorazepate occurs frequently with regular use. Due to the development of tolerance, benzodiazepines are, in general, not considered appropriate for the long-term management of epilepsy; increasing the dose may result only in the developing of tolerance to the higher dose combined with worsened adverse effects. Cross-tolerance occurs between benzodiazepines, meaning that, if individuals are tolerant to one benzodiazepine, they will display a tolerance to equivalent doses of other benzodiazepines. Withdrawal symptoms from benzodiazepines include a worsening of pre-existing symptoms as well as the appearance of new symptoms that were not pre-existing. The withdrawal symptoms may range from mild anxiety and insomnia to severe withdrawal symptoms such as seizures and psychosis. Withdrawal symptoms can be difficult in some cases to differentiate between pre-existing symptoms and withdrawal symptoms. Use of high doses, long-term use and abrupt or over-rapid withdrawal increases increase the severity of withdrawal syndrome.[6] However, tolerance to the active metabolite of clorazepate may occur more slowly than with other benzodiazepines.[6] Regular use of benzodiazepines causes the development of dependence characterised by tolerance to the therapeutic effects of benzodiazepines and the development of the benzodiazepine withdrawal syndromeincluding symptoms such as anxiety, apprehension, tremor, insomnia, nausea, and vomitingupon cessation of benzodiazepine use. Withdrawal from benzodiazepines should be gradual as abrupt withdrawal from high doses of benzodiazepines may cause confusion, toxic psychosis, convulsions, or a condition resembling delirium tremens. Abrupt withdrawal from lower doses may cause depression, nervousness, rebound insomnia, irritability, sweating, and diarrhea.[8]