Clobazam

Medical uses

Clobazam is used for epilepsy. It is unclear if there are any benefits to clobazam over other seizure medications for children with Rolandic epilepsy or other epileptic syndromes.

As of 2005, 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 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 US until October 25, 2011, when it was approved for the adjunctive treatment of seizures associated with Lennox-Gastaut Syndrome in patients 2 years of age or older.

It is also approved for adjunctive therapy for epilepsy in patients who have not responded to first-line drugs and in children who are refractory to first-line drugs. It is not recommended for use in children between the ages of six months and three years, unless there is a compelling need. In addition to epilepsy and severe anxiety, clobazam is also approved as a short-term (2–4 weeks) adjunctive agent in schizophrenia and other psychotic disorders to manage anxiety or agitation.

Clobazam is also available as an oral suspension in the UK, under the trade name of Tapclob.

Clobazam is sometimes used for refractory epilepsies. However, long-term prophylactic treatment of epilepsy has considerable drawbacks, most importantly loss of antiepileptic effects due to tolerance which may render long-term therapy ineffective. Other antiepileptic drugs may therefore be preferred for the long-term management of epilepsy. Furthermore, benzodiazepines 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.

Contraindications

Clobazam should be used with great care in patients with the following disorders:

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

Common

Common side effects include fever, lethargy or sleepiness, drooling, and constipation.

Post Marketing Experience

include other adverse reactions

Warnings and Precautions

In December 2013 the FDA 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 8 weeks of treatment.

Drug interactions

Overdose

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

Tolerance, dependence, and abuse potential

Clobazam in animal studies has been shown to increase reward seeking behaviours which may suggest an increased risk of addictive behavioural patterns. Significant clobazam abuse has been reported in some countries, according to a 1983 World Health Organisation report.

In humans tolerance to the anticonvulsant effects of clobazam may occur and withdrawal seizures can occur during abrupt or overrapid 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 dose and the longer the drug is taken for, the greater the risk of experiencing unpleasant withdrawal symptoms. Withdrawal symptoms can, however, occur from standard dosages and also after short-term use. Benzodiazepine treatment should be discontinued as soon as possible via a slow and gradual dose reduction regimen.

Physical properties

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.

Pharmacology

Clobazam is a GABA-A receptor agonist action and may affect sodium channels and voltage-sensitive calcium channels.

Like other 1,5-benzodiazepines (e.g., arfendazam, lofendazam, CP-1414S), the active metabolite N-desmethyl-clobazam has less affinity for the α₁ subunit of the GABA_A receptor compared to the 1,4-benzodiazepines. It has higher affinity for α₂ containing receptors, where it has positive modulatory activity.

In a double-blind placebo-controlled trial published in 1990 comparing it to clonazepam, 10 mg of clobazam was shown to be less sedating than either 0.5 mg or 1 mg of clonazepam.

The α₁ subtype of the GABA_A receptor, was shown to be responsible for the sedative effects of diazepam by McKernan et al. in 2000, who also showed that its anxiolytic and anticonvulsant properties could still be seen in mice whose α₁ receptors were insensitive to diazepam.

In 1996, Nakamura et al. reported that clobazam and its active metabolite, N-desmethylclobazam (norclobazam), work by enhancing GABA-activated chloride currents at GABA_A-receptor-coupled Cl⁻ channels. 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-desmethyl-clobazam 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.

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.