Carbamazepine
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Carbamazepine
Tegretol (IR, XR, suspension), Carbatrol (ER), Equetro (ER for bipolar), Epitol
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Summary
Common uses
Partial-onset and generalized tonic-clonic seizures (FDA)0, Trigeminal neuralgia (FDA; the first-line and textbook indication)0, Bipolar I mania and mixed episodes (Equetro; FDA)0, Neuropathic pain (off-label)0
Pharmacy
Starting dose
Seizures: 200 mg PO BID, titrate by 200 mg/week to 800-1200 mg/day. Trigeminal neuralgia: 100-200 mg BID, titrate to 200-400 mg TID. Bipolar: 200 mg BID, titrate to 1600 mg/day
Preparations
IR tablets 200 mg; chewable 100 mg; oral suspension 100 mg/5 mL; XR tablets 100, 200, 400 mg (Tegretol XR); ER capsules 100, 200, 300 mg (Carbatrol, Equetro)
US FDA Max
1200 mg/day (adult seizures); 1600 mg/day (bipolar mania)
Pharmacology
Routes
Oral
Onset
Anticonvulsant effect within days; trigeminal neuralgia relief 24-72 hours; mood-stabilizing effect over weeks
Duration
BID-QID dosing (IR); BID for ER formulations
Half-life
Autoinduction: 25-65 hours initially, falling to 12-17 hours after 2-3 weeks of dosing as carbamazepine induces its own CYP3A4 metabolism. Major clinical implication: doses require re-titration after the autoinduction period[2]
Bioavailability
~80% (oral)[2]
Pregnancy
Substantial teratogenic risk including neural tube defects, craniofacial malformations, cardiac defects, and growth restriction; folic acid supplementation and effective contraception are required in reproductive-age patients[2]
Legal status
Rx-only in US
Purported mechanism
Voltage-gated sodium channel blocker in the inactivated state (similar mechanism to lamotrigine), reducing high-frequency repetitive neuronal firing and presynaptic glutamate release. The trigeminal neuralgia efficacy reflects blockade of paroxysmal trigeminal afferent firing.0 Strong CYP3A4 inducer (and autoinducer) producing many interactions: reduces exposure of oral contraceptives, warfarin, lamotrigine, many neuroleptics and antidepressants, antiretrovirals, and direct oral anticoagulants. The HLA-B*15:02 allele substantially elevates Stevens-Johnson syndrome and toxic epidermal necrolysis risk in Asian populations; CPIC and FDA recommend pre-treatment HLA-B*15:02 testing in ancestry-at-risk patients. HLA-A*31:01 confers additional risk in European populations[1]. Rare but recognized aplastic anemia and agranulocytosis warrant periodic CBC monitoring.
References
- ↑ CPIC Guideline for HLA Genotype and Use of Carbamazepine and Oxcarbazepine, 2017. https://cpicpgx.org/guidelines/guideline-for-carbamazepine-and-hla-b/
- ↑ 2.0 2.1 2.2 FDA Prescribing Information, Tegretol (carbamazepine), Novartis, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2018/016608s120,018281s069lbl.pdf