Clobazam

Medical uses

Clobazam belongs to the benzodiazepine class of drugs. As a long-acting benzodiazepine derivative it is primarily used as a sedative-hypnotic, anxiolytic, and as an adjunctive therapy in epilepsy.

As an adjunctive therapy in epilepsy, it is used in patients who have not responded to first-line drugs and in children who are refractory to first-line drugs. It is unclear if there are any benefits to clobazam over other seizure medications for children with Rolandic epilepsy or other epileptic syndromes. It is not recommended for use in children between the ages of six months and three years, unless there is a compelling need.

Clobazam is sometimes used for refractory epilepsies. However, long-term prophylactic treatment of epilepsy may have considerable drawbacks, most importantly decreased antiepileptic effects due to drug tolerance which may render long-term therapy less effective. Other antiepileptic drugs may therefore be preferred for the long-term management of epilepsy. Furthermore, benzodiazepines may have the drawback, particularly after long-term use, of causing rebound seizures upon abrupt or over-rapid discontinuation of therapy forming part of the benzodiazepine withdrawal syndrome.

Clobazam is approved in Canada for add-on use in tonic–clonic, complex partial, and myoclonic seizures. Clobazam is approved for adjunctive therapy in complex partial seizures, certain types of status epilepticus, specifically the myoclonic, myoclonic-absent, simple partial, complex partial, and tonic varieties, and non-status absence seizures. It is also approved for the treatment of anxiety.

In India, clobazam is approved for use as an adjunctive therapy in epilepsy, and in acute and chronic anxiety. In Japan, clobazam is approved for adjunctive therapy in treatment-resistant epilepsy featuring complex partial seizures. In New Zealand, clobazam is marketed as Frisium. In the United Kingdom clobazam (Frisium) is approved for short-term (2–4 weeks) relief of acute anxiety in patients who have not responded to other drugs, with or without insomnia and without uncontrolled clinical depression. It was not approved in the United States until October 2011, when it was approved for the adjunctive treatment of seizures associated with Lennox–Gastaut syndrome in people aged two years of age or older.

In the United States, clobazam is indicated for use in combination with other medicines to control seizures in people aged two years of age and older who have a specific severe form of epilepsy called Lennox–Gastaut syndrome.

Clinical efficacy and tolerability for management of chronic epilepsy and anxiety disorders has been established in multiple studies.

Side effects

In September 2020, the US Food and Drug Administration required the boxed warning be updated for all benzodiazepine medicines to describe the risks of abuse, misuse, addiction, physical dependence, and withdrawal reactions consistently across all the medicines in the class.

Common

Common side effects include fever, drooling, and constipation.

Warnings and precautions

In December 2013, the US Food and Drug Administration added warnings to the label for clobazam, that it can cause serious skin reactions, Stevens–Johnson syndrome, and toxic epidermal necrolysis, especially in the first eight weeks of treatment.

Overdose

Overdose and intoxication with benzodiazepines, including clobazam, may lead to CNS depression, associated with drowsiness, confusion, and lethargy, possibly progressing to ataxia, respiratory depression, hypotension, and coma or death. The risk of a fatal outcome is increased in cases of combined poisoning with other CNS depressants, including alcohol.

Abuse potential and addiction

Classic (non-anxioselective) benzodiazepines in animal studies have been shown to increase reward-seeking behaviours which may suggest an increased risk of addictive behavioural patterns. Clobazam abuse has been reported in some countries, according to a 1983 World Health Organization report.

Dependence and withdrawal

In humans, tolerance to the anticonvulsant effects of clobazam may occur and withdrawal seizures may occur during abrupt or over-rapid withdrawal.

Clobazam as with other benzodiazepine drugs can lead to physical dependence, addiction, and what is known as the benzodiazepine withdrawal syndrome. Withdrawal from clobazam or other benzodiazepines after regular use often leads to withdrawal symptoms which are similar to those seen during alcohol and barbiturate withdrawal. The higher the dosage and the longer the drug is taken, the greater the risk of experiencing unpleasant withdrawal symptoms. Benzodiazepine treatment should only be discontinued via a slow and gradual dose reduction regimen.

Pharmacology

Clobazam is predominantly a positive allosteric modulator at the GABAA receptor to increase GABAergic transmission, particularly chloride conductance in neurons and with some speculated additional activity at sodium channels and voltage-sensitive calcium channels.

The exact mechanism of action for clobazam, a 1,5-benzodiazepine, which has sedative-hypnotic, anxiolytic, and anticonvulsant effects similar to those produced by other benzodiazepine derivatives, but is a partial agonist at the GABAA receptors. Clobazam is thought to involve the potentiation of GABAergic neurotransmission resulting from binding at the benzodiazepine site of the GABAA receptor. Like other 1,5-benzodiazepines (for example, arfendazam, lofendazam, triflubazam, and CP-1414S), the active metabolite N-desmethylclobazam has less affinity for the α1 subunit of the GABAA receptor compared to the 1,4-benzodiazepines. It has higher affinity for the α2 subunit of the GABAA receptor, which mediates anxiolytic effects, than the α1 subunit. Clobazam also has positive modulatory activity.

Clobazam and its active metabolite, N-desmethylclobazam (norclobazam), work by enhancing GABA-activated chloride influx at GABAA receptors, creating a hyperpolarizing, inhibitory postsynaptic potential. It is the primary active metabolite of clobazam, crucial for its prolonged anti-seizure and anti-anxiety effects, acting similarly on GABAA receptors but with potentially greater importance in long-term therapy, especially for epilepsy, and is largely responsible for the drug's overall clinical action. It was also reported that these effects were inhibited by the GABA antagonist flumazenil, and that clobazam acts more efficiently in GABA-deficient brain tissue.

Metabolism

Clobazam has two major metabolites: N-desmethylclobazam and 4-hydroxyclobazam, the former of which is active. The demethylation is facilitated by CYP2C19, CYP3A4, and CYP2B6 and the 4-hydroxyclobazam by CYP2C18 and CYP2C19.

In children, clobazam half-life values is average 16 hours, while in the elderly, clobazam half-life values are 30 to 48 hours.

Chemistry

Clobazam is a 1,5-benzodiazepine, meaning that its diazepine ring has nitrogen atoms at the 1 and 5 positions (instead of the usual 1 and 4).

It is not soluble in water and is available in oral form only.

History

Clobazam was discovered at the Maestretti Research Laboratories in Milan and was first published in 1969; Maestretti was acquired by Roussel Uclaf which became part of Sanofi.

References

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