Carbamazapine

Question 1

Indications

Answer 1

1. Epilepsy, as a first choice treatment for focal seizures with and without secondary generalisation and for primary generalised seizures.
2. Trigeminal neuralgia, as first choice treatment to control pain and reduce frequency and severity of attacks.
3. Bipolar disorder, as an option for prophylaxis in patients resistant to or intolerant of other medication.

Question 2

Mechanisms of action

Answer 2

The mechanism of action of carbamazepine is incompletely understood. It appears to inhibit neuronal sodium channels, stabilising resting membrane potentials and reducing neuronal excitability (see Phenytoin). This may inhibit spread of seizure activity in epilepsy, control neuralgic pain by blocking synaptic transmission in the trigeminal nucleus and stabilise mood in bipolar disorder by reducing electrical ‘kindling’ in the temporal lobe and limbic system.

Question 3

Adverse effects

Answer 3

The most common dose-related adverse effects are gastrointestinal upset (e.g. nausea and vomiting) and neurological effects (particularly dizziness and ataxia). Carbamazepine hypersensitivity affects about 10% of people taking the drug and most commonly manifests as a mild maculopapular skin rash. Antiepileptic hypersensitivity syndrome affects about 1 in 5000 people taking carbamazepine or phenytoin, usually within 2 months of starting treatment. Clinical features include severe skin reactions (e.g. Stevens–Johnson syndrome, toxic epidermal necrolysis), fever and lymphadenopathy with systemic (e.g. haematological, hepatic, renal) involvement and mortality of about 10%. Other common adverse effects include oedema and hyponatraemia due to an antidiuretic hormone-like effect.

Question 4

Warnings

Answer 4

Exposure in utero is associated with neural tube, cardiac, and urinary abnormalities.

Prior sensitivity to antiepileptics is a contraindication

Question 5

Interactions

Answer 5

P450 inducer (lowers conc of warfarin, oestrogens etc)

Metabolised by P450 so concentration increased by P450 inhibitors.

Question 6

Prescribing

Answer 6

PO or PR

Question 7

Administration

Answer 7

Immediate or modified-release

Question 8

Communication

Answer 8

See other anti-epileptics