Antiseizure medications · Neurology
Carbamazepine
Tegretol®(brand names vary by market)
Induces its own metabolism, and everyone else's.
Also: modified release, oral liquid
Mechanism
Use-dependent sodium channel blockade, stabilising the inactivated state and limiting repetitive firing.
Indications
- Focal seizures
- Trigeminal neuralgia, where it is first-line and dramatically effective
- Bipolar disorder
Formulations
Dosing concepts
Auto-induction
It induces the enzymes that clear it, so levels fall over the first weeks on an unchanged dose. Titration accounts for this; a stable dose at week one is often sub-therapeutic by week four.
HLA screening
HLA-B*1502 carries a strongly increased risk of Stevens-Johnson syndrome and toxic epidermal necrolysis, and screening is recommended before starting in patients of Han Chinese, Thai and other South-East Asian ancestry.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~80%
- Half-life
- 25 to 65 h initially, falling to 12 to 17 h after auto-induction
- Elimination
- hepatic: CYP3A4, and a potent inducer of CYP3A4, CYP2C9 and P-glycoprotein
- Protein binding
- ~75%
Adverse effects
- Dizziness, diplopia, ataxiacommonDose-related and often worst at peak concentration, which splitting the dose can fix.
- Hyponatremia (SIADH)common & seriousCommon enough that sodium is monitored routinely, and the usual cause of confusion on this drug.
- Rash, including severe cutaneous reactionsserious
- Leukopenia and aplastic anemiaserious
- Hepatotoxicityserious
Contraindications & precautions
Contraindications
- Bone marrow depression
- Prior severe cutaneous reaction
- Concurrent or recent MAO inhibitor
- AV block
Precautions
- Ancestry-based HLA-B*1502 risk
- Hyponatremia or concurrent diuretics
- Any drug it will induce
Interactions
Monitoring
Sodium
SIADH is common and is the usual cause of confusion, falls or seizure breakthrough · Baseline, a few weeks in, then periodically
Full blood count and liver enzymes
Marrow and hepatic toxicity
Level once auto-induction has settled
Early levels do not predict steady state
Efficacy of every co-prescribed drug it induces
Contraceptives, anticoagulants, immunosuppressants and antiretrovirals all fall
Counselling points
- Report any rash immediately, especially in the first two months.
- Tell us about fever, sore throat, mouth ulcers or unusual bruising.
- It reduces the effectiveness of hormonal contraception; we need to discuss alternatives.
- Avoid grapefruit juice.
- Confusion or unsteadiness can mean a low sodium and needs a blood test.
Clinical pearls
- It is a potent enzyme inducer, so the harm often shows up as another drug failing rather than as a side effect: an unexpected pregnancy, a clot on a DOAC, a rejected transplant.
- For trigeminal neuralgia it is unusually effective, to the point that a poor response should prompt a rethink of the diagnosis.
References & review
- Carbamazepine product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.