carbamazepine: clinical use

Prescribing considerations

• Confirm seizure type; carbamazepine is generally unsuitable for absence and myoclonic seizures.
• Maintain manufacturer continuity for epilepsy and clinically manage formulation changes.
• Screen for HLA-B*1502 before initiation in people of Han Chinese or Thai ancestry where possible; consider risk in other susceptible Asian populations.
• Review pregnancy potential, contraception and interactions.
• Avoid abrupt withdrawal and consider falls risk.

Contraindications and cautions

• Hypersensitivity to carbamazepine, formulation ingredients or structurally related medicines such as tricyclic antidepressants
• Atrioventricular block
• History of bone-marrow depression
• History of hepatic porphyria
• Concurrent monoamine oxidase inhibitor treatment

Monitoring

• Before treatment, assess full blood count, liver and renal function, electrolytes including sodium, body weight and relevant HLA status.
• Consider ECG for cardiovascular disease or risk and vitamin D assessment where appropriate.
• Monitor electrolytes and liver function periodically; monitor sodium more closely with renal impairment or sodium-lowering medicines.
• Check thyroid function in people with hypothyroidism.
• Concentrations may help assess suspected toxicity, non-adherence, loss of seizure control, pregnancy or pharmacokinetic interactions.
• Investigate fever, sore throat, rash, mouth ulcers, bruising, bleeding, progressive leucopenia or worsening liver dysfunction promptly.

Clinical pharmacology

Carbamazepine produces use- and voltage-dependent sodium-channel blockade. It is extensively metabolised by the liver, forms an active epoxide metabolite and induces CYP3A4 and other enzyme systems, including its own metabolism.

Formulation and product differences

• Conventional tablets are immediate release.
• Oral suspension must be shaken and contains sorbitol and other excipients.
• Prolonged-release tablets reduce peak-to-trough fluctuation and must not be chewed.
• Chewtabs are chewed before swallowing and contain sorbitol.
• Suppositories are rectal, licensed only for epilepsy and used temporarily when oral treatment is not possible.
• Bioavailability can differ between preparations, affecting seizure control or adverse effects.

Modified-release tablet

Route: Oral

Strengths: 200 mg, 400 mg

Oral suspension

Route: Oral

Strengths: 100 mg/5 mL

Tablet

Route: Oral

Strengths: 100 mg, 200 mg, 400 mg