💊 Carbamazepine

Carbamazepine is an antiepileptic drug (AED) and a mood stabiliser, structurally related to tricyclic antidepressants. It is primarily used for focal seizures and trigeminal neuralgia.

Carbamazepine primarily acts by blocking voltage-gated sodium channels in the neuronal membrane. This stabilises the inactivated state of the sodium channels, preventing repetitive neuronal firing and reducing the propagation of seizure activity. It also has some effects on calcium channels and neurotransmitter systems.

Carbamazepine is a first-line treatment for focal (partial) seizures, with or without secondary generalisation. It is also highly effective for the treatment of trigeminal neuralgia, providing significant pain relief. In some cases, it can be used as a mood stabiliser in bipolar disorder, particularly for manic episodes.

Contraindications include a history of bone marrow depression, acute porphyria, and hypersensitivity to carbamazepine or tricyclic antidepressants. Concomitant use with MAOIs is contraindicated. Caution is required in patients with cardiac conduction abnormalities or significant hepatic or renal impairment.

Common adverse effects include dizziness, drowsiness, ataxia, nausea, and blurred vision. More serious but less common effects include hyponatraemia (due to SIADH), blood dyscrasias (e.g., aplastic anaemia, agranulocytosis), and severe skin reactions (e.g., Stevens-Johnson syndrome, TEN), particularly in certain genetic predispositions (e.g., HLA-B*1502).

Baseline and regular monitoring of full blood count (FBC), liver function tests (LFTs), and electrolytes (especially sodium) is crucial, particularly during the initial months of treatment. Therapeutic drug monitoring may be useful to guide dosage adjustments and assess compliance. Patients should be monitored for signs of skin reactions.

Check for allergies and counsel patients about common side effects like dizziness and drowsiness. Emphasise the importance of reporting any skin rash, fever, or mouth ulcers immediately. Warn about potential interactions with other medications due to its enzyme-inducing properties, which can reduce the efficacy of hormonal contraceptives.

Carbamazepine is a potent enzyme inducer, leading to significant drug interactions (e.g., reduced efficacy of oral contraceptives). Remember the risk of hyponatraemia and severe skin reactions (SJS/TEN), particularly in Asian populations (HLA-B*1502). First-line for focal seizures and trigeminal neuralgia. Monitor FBC, LFTs, and electrolytes.

SBA questions often highlight the risk of hyponatraemia and severe skin reactions (SJS/TEN), especially in specific ethnic groups. Scenarios might present a patient with focal seizures or trigeminal neuralgia and ask about appropriate monitoring or adverse effect counselling. Questions may also test knowledge of drug interactions due to its potent enzyme-inducing properties.