carbamazepine

Brand: Tegretol, Carbatrol, Equetro

⚠ BBW Beers Criteria TDM Required Prototype: phenytoin

Drug Class: antiepileptic

Drug Family: antiepileptic

Subclass: iminostilbene

Organ Systems: cns

Mechanism of Action

Blocks voltage-gated sodium channels in the inactivated state, reducing sustained repetitive neuronal firing; also used in neuropathic pain and bipolar disorder via sodium and calcium channel modulation.

voltage-gated sodium channels

Indications

focal and generalized tonic-clonic seizures
trigeminal neuralgia
bipolar disorder (manic episodes)

Contraindications

bone marrow suppression history
MAOIs within 14 days
patients of Han Chinese or Thai descent without HLA-B*1502 testing (SJS risk)
hepatic porphyria

Adverse Effects

Common

diplopia
ataxia
dizziness
nausea
leukopenia

Serious

aplastic anemia
agranulocytosis
Stevens-Johnson syndrome
DRESS syndrome
SIADH
hepatotoxicity

Pharmacokinetics (ADME)

Absorption	Slowly absorbed; bioavailability ~80%
Distribution	Protein binding ~75%; Vd 0.8–1.9 L/kg; crosses BBB and placenta
Metabolism	CYP3A4 (primarily); auto-induces own metabolism — half-life shortens with chronic use from ~36 hours to 12–17 hours
Excretion	Urine 72%, feces 28%; <3% unchanged
Half-life	12–17 hours (chronic; initially 25–65 hours)
Onset	Days to weeks for full effect
Peak	4–5 hours (immediate release)
Duration	12–24 hours
Protein Binding	~75%
Vd	0.8–1.9 L/kg

Drug Interactions

Drug / Agent	Mechanism	Severity
oral contraceptives	CYP3A4 induction reduces contraceptive levels	major
valproate	carbamazepine metabolism increased; valproate levels decreased	moderate
MAOIs	structural similarity to TCAs; serotonin syndrome/hypertensive crisis risk	major

Nursing Considerations

Obtain baseline CBC and LFTs; monitor CBC every 2–4 weeks for first 3 months; hold if ANC <1500/mm³
Therapeutic serum level: 4–12 mcg/mL; monitor levels 2–4 weeks after dose changes due to auto-induction
Screen patients of Asian descent for HLA-B*1502 allele before initiation to assess Stevens-Johnson syndrome risk
Instruct patient to report rash, fever, oral sores, or unusual bruising immediately; avoid abrupt discontinuation

Clinical Pearls

Carbamazepine auto-induces CYP3A4, causing its own half-life to decrease by 50% over the first months of therapy — levels must be rechecked after 4–6 weeks
First-line for trigeminal neuralgia; the number needed to treat (NNT) for pain relief is approximately 2

Safety Profile

Pregnancy use-with-caution

Lactation use-with-caution

Renal Adjustment Not required

Hepatic Adjustment Required

TDM Required

Concordance Terms

Cross-referenced clinical concepts — click any term to see all content where it appears.

Antiepileptic Bipolar Disorder (manic Episodes) Focal And Generalized Tonic-clonic Seizures Trigeminal Neuralgia

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