Carbamazepine is a first-generation anticonvulsant and mood-stabilizing agent, structurally related to tricyclic antidepressants. It is a cornerstone therapy for focal (partial) seizures and trigeminal neuralgia in India, and is also a primary treatment for bipolar disorder. It works primarily by blocking voltage-gated sodium channels, stabilizing hyper-excitable neuronal membranes, and inhibiting repetitive neuronal firing.
Adult: Epilepsy: Initial: 100-200 mg once or twice daily. Increase slowly by 200 mg/day at weekly intervals. Usual maintenance: 800-1200 mg/day in 2-4 divided doses. Max: 1600-2000 mg/day. Trigeminal Neuralgia: Initial: 100 mg twice daily. Increase by up to 200 mg/day until pain relief (usual range 400-800 mg/day). Bipolar Disorder: 400-1600 mg/day in divided doses.
Note: Administer with meals to improve tolerance and reduce GI upset. Tablets should be swallowed whole with a glass of water. Do not crush or chew. Doses should be evenly spaced. Consistency in timing with respect to food is important.
Carbamazepine's primary mechanism involves use-dependent blockade of voltage-gated sodium channels in the neuronal membrane. It binds preferentially to the inactivated state of the channel, preventing the return to the resting state and thereby inhibiting the generation of repetitive action potentials. This stabilizes hyper-excitable neurons and reduces synaptic transmission.
Pregnancy: Pregnancy Category D (US FDA). Known teratogen. Risk of neural tube defects (spina bifida), craniofacial defects, cardiovascular malformations, and developmental delay. Use only if benefit outweighs risk. Folic acid supplementation (5 mg/day) recommended before and during pregnancy. Monitor drug levels as pharmacokinetics change. Consider switching to a safer anticonvulsant (e.g., levetiracetam) pre-conception if possible.
Driving: May impair mental and/or physical abilities required for driving or operating machinery, especially during initiation and dose titration. Patients should be cautioned not to drive until they know how the medication affects them.
| Phenytoin, Phenobarbital | Mutual metabolism induction; decreased levels of both drugs. | Major |
| Valproic Acid / Sodium Valproate | Inhibits metabolism of carbamazepine epoxide; increases toxic epoxide levels. Valproate levels may decrease. | Major |
| Warfarin | Carbamazepine decreases warfarin efficacy; requires increased warfarin dose and frequent INR monitoring. | Major |
| Oral Contraceptives (Ethinyl Estradiol) | Carbamazepine induces metabolism, causing contraceptive failure. Use non-hormonal or high-dose OC methods. | Major |
| Clarithromycin, Erythromycin, Fluconazole, Ketoconazole | CYP3A4 inhibitors; significantly increase carbamazepine levels, leading to toxicity. | Major |
| Lithium | Increased neurotoxic effects (ataxia, tremor, confusion) even with normal lithium levels. | Moderate |
| Lamotrigine | Carbamazepine decreases lamotrigine levels. Lamotrigine may increase risk of CBZ neurotoxicity. | Moderate |
| Risperidone, Haloperidol | Decreases antipsychotic levels; may need dose adjustment. | Moderate |
| Digoxin | Decreases digoxin levels. | Moderate |
| Theophylline | Decreases theophylline levels. | Moderate |