Carbamazepine is chemically similar to the tricyclic antidepressant drugs. It is most commonly used in the treatment of epilepsy, particularly partial seizures, where carbamazepine remains a first-line medication. Other uses include

• trigeminal neuralgia
• bipolar disorder

Mechanism of action

• binds to sodium channels increases their refractory period
• Carbamazepine binds to voltage-gated sodium channels in the neuronal cell membrane in their inactive form. Here, they block voltage-gated sodium channel action and thus takes longer for the neurone to depolarize - increasing the absolute refractory period. This increases the threshold for seizure activity that helps prevent epileptic seizures.

Adverse effects

• P450 enzyme inducer
• dizziness and ataxia
• drowsiness
• headache
• visual disturbances (especially diplopia)
• Steven-Johnson syndrome
• leucopenia and agranulocytosis
• hyponatraemia secondary to syndrome of inappropriate ADH secretion

Carbamazepine is known to exhibit autoinduction, hence when patients start carbamazepine they may see a return of seizures after 3-4 weeks of treatment.