​Pharmacology - Carbamazepine

​Pharmacology - Carbamazepine 
Carbamazepine Action Anticonvulsant. Relieves neuropathic pain.

Mode of Action Blocks Na+ channels to impede action potential start and propagation. Use-dependence of block means that action is selectively on rapidly firing neurons in the epileptic center.
Oral admin. Metabolised by P450 system in liver to create an active metabolite. T0.5 30h. Phenytoin T0.5 20h but increases with dosage due to saturation kinetics.

Use in Clinical Settings
Partial and generalised seizures (tonic-clonic), but not absence seizures. Also neuropathic pain and bipolar disorder. Phenytoin also used for status epilepticus. Saturable clearance of phenytoin makes it useful to monitor its plasma levels.

Allergies and Reactions
Drowsiness, headache, mental confusion, motor difficulties. Rare, but serious: liver damage, agranulocytosis, aplastic anaemia, skin response. Teratogenic eects (e.g. cleft palate with phenytoin).
Phenytoin may induce thickness of the gums and hirsutism.

Induction of cytochrome P450 enzymes causes several medication interactions (e.g. ineectiveness of oestrogenic contraceptives). Oxcarbazepine substantially weaker P450 inducer.