Carbamazepine

Brand Names: Tegretol

Drug Class: Anticonvulsant, Sodium Channel Blocker

Overview

Carbamazepine is an anticonvulsant and specific analgesic for trigeminal neuralgia. It stabilizes hyperexcited neuronal membranes by inhibiting voltage-gated sodium channels, reducing synaptic transmission. It is used for epilepsy (partial and generalized tonic-clonic seizures) and neuropathic pain conditions.

Mechanism of Action

Carbamazepine exerts its anticonvulsant and analgesic effects primarily by blocking voltage-gated sodium channels, stabilizing hyperexcitable neuronal membranes, inhibiting repetitive neuronal firing, and reducing synaptic transmission. It may also modulate neurotransmitter release.

Indications

  • Partial seizures with complex symptomatology
  • Generalized tonic-clonic seizures
  • Trigeminal neuralgia

Common Doses

  • 100 mg
  • 200 mg
  • 300 mg
  • 400 mg

Dosage

Start low and titrate slowly based on indication and patient age. For epilepsy in adults: initial 200 mg twice daily, increase weekly by up to 200 mg/day to maintenance 800-1200 mg/day. For trigeminal neuralgia: initial 100 mg twice daily, titrate to 400-800 mg/day. Use extended-release formulations twice daily and suspension four times daily.

Contraindications

  • History of bone marrow depression
  • Hypersensitivity to carbamazepine or tricyclic compounds
  • Concurrent use with MAO inhibitors (discontinue MAOI ≥14 days prior)
  • Coadministration with nefazodone

Side Effects

  • Dizziness, drowsiness, ataxia, nausea, vomiting
  • Leukopenia, thrombocytopenia, aplastic anemia
  • Rash, Stevens-Johnson syndrome, toxic epidermal necrolysis
  • Hyponatremia, hepatic enzyme elevations
  • Blurred vision, diplopia, nystagmus

Interactions

  • Strong CYP3A4 inducers (e.g., phenytoin, phenobarbital) decrease carbamazepine levels
  • Carbamazepine induces CYP3A4, reducing levels of oral contraceptives, warfarin, many antipsychotics
  • Avoid simultaneous administration of suspension with liquid chlorpromazine/thioridazine (precipitate formation)
  • Increased toxicity with other sodium channel blockers

Counseling Points

  • Take with food to minimize GI upset
  • Do not crush or chew extended-release tablets
  • Suspension should not be mixed with other liquids
  • Report fever, sore throat, mouth ulcers, rash, or easy bruising immediately
  • Avoid abrupt discontinuation
  • Use effective non-hormonal contraception
  • May cause dizziness/drowsiness; avoid driving until effects known