Carbamazepine (Psychiatric Use)

How it works

It stabilises hyperexcitable neuronal membranes mainly by blocking voltage-gated sodium channels, reducing repetitive neuronal firing and pathological neurotransmission.

Prescribing in practice

• It is a potent inducer of hepatic enzymes and therefore reduces the effectiveness of many co-prescribed drugs, including hormonal contraceptives, so interaction checks are essential.
• Warn patients about signs of blood, liver and skin disorders (including potentially life-threatening rashes such as Stevens-Johnson syndrome) and the increased serious-cutaneous-reaction risk associated with the HLA-B*1502 allele in relevant ancestries.
• It is teratogenic and should be avoided in pregnancy and in women of childbearing potential not using effective contraception unless there is no safer alternative.

Monitoring

Monitor full blood count, liver function and, where indicated, plasma carbamazepine concentration, alongside review of mood and emergent rashes.

Counselling the patient

• Seek urgent medical advice if you develop a fever, mouth ulcers, bruising, a rash or yellowing of the skin.
• This drug can stop hormonal contraception working, so discuss reliable contraception.
• Do not stop suddenly without medical advice.

Evidence & guidelines

Carbamazepine is recognised in NICE guidance as a mood-stabilising option in bipolar disorder; MHRA advice highlights teratogenicity and serious cutaneous reactions.