carbamazepine

Quick answers

What is carbamazepine?

Carbamazepine is a voltage-gated sodium channel blocker used off-label as a mood stabiliser for acute mania, mixed episodes, and rapid-cycling bipolar disorder when lithium or valproate are not tolerated.

What is TEGRETOL?

TEGRETOL is a brand name for carbamazepine.

What is TEGRETOL (carbamazepine) used for?

Label indications include: Seizures (various types); trigeminal neuralgia; off‑label for bipolar mania (consult guidelines).

What drug class is TEGRETOL (carbamazepine)?

Mood Stabilizer.

What is the mechanism of action of TEGRETOL (carbamazepine)?

Voltage‑gated sodium channel blocker; reduces high‑frequency neuronal firing.

What strengths does TEGRETOL (carbamazepine) come in?

Immediate-release tablets/chewables 100–200 mg, oral suspension 100 mg/5 mL, extended-release tablets/capsules 100–400 mg.

Is TEGRETOL (carbamazepine) a controlled substance?

No — it is not scheduled as a controlled substance under U.S. federal law.

General information

Considered second-line in bipolar disorder due to complex kinetics, hematologic risk, and drug interactions; valuable in mixed and rapid-cycling presentations.

Mechanism of action

Refer to the Glossary entry on Neurotransmitters for background on receptor systems involved in serious mental illness.

• Voltage-gated sodium channel blocker with downstream modulation of excitatory neurotransmission.

Metabolism & pharmacokinetics

• Oral bioavailability 70–80%; peak 4–8 h (IR) or 6–24 h (XR).
• Metabolized via CYP3A4 to active 10,11-epoxide; autoinduction lowers half-life to 12–17 h after chronic dosing.
• Eliminated renally as metabolites.
• Autoinduction develops over the first several weeks; serum levels may fall after an initially stable dose, so a planned level recheck after 3–4 weeks helps avoid underdosing.

Dosing & administration

• Typical start is 200 mg BID; increase by 200 mg/day every 3–5 days to 800–1,200 mg/day (max 1,600 mg).
• Target serum concentration 4–12 µg/mL; levels are often checked 3–5 days after dose changes and again after 3–4 weeks to account for autoinduction.
• When sedation, dizziness, or diplopia limit titration, slower dose increases (smaller steps with longer intervals) are often better tolerated than rapid escalation.

Monitoring & labs

• Baseline: CBC (including WBC/ANC), LFTs, sodium; HLA-B*1502 testing in at-risk ancestry.
• Ongoing: periodic CBC, LFTs, and sodium; monitoring for rash and hyponatremia/SIADH.
• Serum levels: trough monitoring can be helpful in select cases; autoinduction and strong CYP induction create many drug interactions.
• Recheck serum level after 3–4 weeks on a stable dose to account for autoinduction, and again after adding or stopping strong CYP3A4 inhibitors/inducers.
• Medication reconciliation at each visit (oral contraceptives, warfarin or other anticoagulants, antipsychotics) because enzyme induction can lower exposure and change clinical response.
• Contraception interactions and rash/fever warning signs are typically reviewed.

Sources: FDA label; guideline recommendations; pharmacogenetics advisories. Because carbamazepine is a strong inducer with autoinduction, documentation of the monitoring plan (CBC/LFT/sodium cadence, level timing, and contraception counseling) helps reduce avoidable adverse events, especially in complex polypharmacy in most clinical settings.

Adverse effects

Interactions

• Strong inducer of CYP3A4, CYP1A2, CYP2C, and UGT—reduces levels of antipsychotics, antidepressants, oral contraceptives.
• Reduced hormonal contraceptive efficacy is common; backup or non-hormonal contraception planning is typically discussed when pregnancy is possible.
• Enzyme induction can also lower exposure to some anticoagulants and other narrow-therapeutic-index drugs; clinical response monitoring and dose adjustments are often needed rather than assuming medication failure.
• CYP3A4 inhibitors (erythromycin, ketoconazole) raise carbamazepine levels—risk toxicity.
• Valproate inhibits epoxide hydrolase, increasing active metabolite; toxicity monitoring is important.

Other useful information

• Baseline labs typically include CBC, CMP, pregnancy test, and HLA screening (as indicated).
• Contraception planning matters because carbamazepine reduces efficacy of hormonal contraceptives.
• Rash and infection symptoms requiring urgent evaluation are typically reviewed with patients.
• Printable counselling guidance from the carbamazepine print page can reinforce contraception planning and monitoring expectations.
• Abrupt discontinuation is generally avoided; tapering plans help prevent seizure rebound (in epilepsy) and mood destabilization (in bipolar disorder).
• Grapefruit or other strong CYP3A4 inhibitors can raise carbamazepine levels and are generally avoided; sudden level increases can lead to dizziness, diplopia, and ataxia.

References