Carbamazepine acts by binding to the sodium channels of neuronal membranes and prevents the influx of sodium into the cell which normally leads to an action potential. By preventing depolarisation of these neurones, there is not the repeated "firing" of action potentials that is responsible for epileptic seizures.
Carbamazepine has a significant side effect profile.
Two of the most serious side effects are dermatological conditions: Stevens - Johnson syndrome and Toxic Epidermal Necrolysis. Both of these can be life-threatening, and are more common in Asian populations than Caucasians, due to Asians possessing particular genetic alleles. Before deciding to initiate treatment, patients of Han Chinese and Thai origin should whenever possible be screened for HLA-B*1502 as this allele strongly predicts the risk of severe carbamazepine-associated Stevens-Johnson Syndrome.
Carbamazepine can induce Syndrome of Inappropriate Anti-Diuretic Hormone Secretion.
Blood disorders are also a common side effect of carbamazepine.
Common side effects of Carbamazepine which are less serious include:
- Nausea and vomiting
- Dry mouth
- Peripheral Oedema, weight gain
- Dizziness
- Drowsiness and fatigue
- Headache
- Abnormal LFTs
Some side effects are dose related and are more common at the start of treatment and in the elderly. Further detail can be found in the BNF.
Carbamazepine is like phenytoin in that it is also metabolised via the cytochrome P450 system in the liver. As it acts as an enzyme inducer, it is notorious for affecting a whole host of other drugs that are metabolised via the CP450 system - most notably anticoagulants (such as apixaban, dabigatran and warfarin) and the oral contraceptive pill. Higher doses of these drugs may be needed in order to provide their therapeutic effects or alternative treatments may need to be considered.
Bioavailability may vary between different pharmaceutical preparations, so this is one of the rare instances where it is useful to prescribe by brand name.
