Product Description

Clobazam

Clobazam is a drug which is a benzodiazepine derivative. It has been marketed as an anxiolytic since 1975 and an anticonvulsant since 1984.
Pharmacology

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). Like other 1,5-benzodiazepines (arfendazam, lofendazam, eg.), it has less affinity for the ω1-allosteric binding site on the GABAA receptor compared to the 1,4-benzodiazepines. It has selective affinity for the ω2 site, where it has agonistic activity.

In a double-blind placebo-controlled trial published in 1990 comparing it to clonazepam, 10mg or 20 mg of clobazam was shown to be much less sedating than either 0.5mg or 1 mg of clonazepam.

The ω1-receptor, which is found on the α1 subtype of the GABAA 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. It would seem, then, that the anticonvulsant properties of clobazam are due to its selective affinity for ω2.

In 1996, Nakamura et al reported that clobazam and its active metabolite, N-desmethylclobazam (norclobazam), work by enhancing GABA-activated chloride currents at GABAA-receptor-coupled Cl- channels. It was also reported that these effects were inhibited by the GABA antagonist flumazenil, and that clobazam acts most efficiently in GABA-deficient brain tissue.

Nine years earlier, Kilpatrick et al noted that there was a correlation between plasma levels of norclobazam and therapeutic effects, although this was not true with the parent compound.

According to Valli and colleagues in 1984, clobazam lowered prolactin levels elevated by sulpiride, a typical antipsychotic. Hyperprolactinaemia (ie. elevated blood prolactin) occurs occasionally in people using antipsychotics, (particularly the typical ones), and can lead to cardiovascular disease, breast cancer, galactorrhea, infertility, amenorrhea, dysmenorrhea, osteopaenia, osteoporosis, loss of libido, impotence, and hypogonadism.

Antipsychotics block type 2 dopamine receptors and at least 65% of central D2 receptors need to be occupied to produce a response; >72% D2 receptor occupancy was found to be associated with development of hyperprolactinaemia.

Peak plasma protein binding occurs around 83%.
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.
Uses
Approved
Canada

As of 2005, clobazam (Frisium®) is approved in Canada for adjunctive use in tonic-clonic, complex partial, and myoclonic seizures.
France

Clobazam (Urbanyl®) 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.
India

Clobazam (Frisium®, Aventis Pharma India, Ltd.) is approved for use as an adjunctive therapy in epilepsy and in acute and chronic anxiety.
Japan

Clobazam (Mystan®) is approved for adjunctive therapy in treatment-resistant epilepsy featuring complex partial seizures.
New Zealand

Marketed as: Frisium®
United Kingdom

Clobazam (Frisium®) is approved in the United Kingdom 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 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 an adjunctive agent in schizophrenia and other psychotic disorders.
Dosage

Clobazam is available in oral form only, due to its insolubility in water.
Side effects
Common
Ataxia
Somnolence
Diplopia
Dysarthria
Rare
Gelastic seizures
Urticaria
Rashes
Contraindications

Clobazam should be used with great care in patients with the following disorders:
Myasthenia gravis
Sleep apnoea
Severe liver diseases such as cirrhosis and hepatitis
Respiratory problems, including hypoventilation
Drug Interactions
Alcohol increases bioavailability by 50%
Cimetidine increases the effects of clobazam
valproates