Generic Name

Sodium‑channel blockade

Mechanism

• Sodium‑channel blockade: Stabilizes the inactive state of voltage‑gated Na⁺ channels, reducing high‑frequency firing of neurons.
• Decreases glutamate release: Modulates excitatory neurotransmission.
• Metabolic inhibition: Suppresses 2,3‑epoxides of phenobarbital, affecting enzyme pathways.

Pharmacokinetics

• Absorption: Rapid, oral peak ≈ 1–2 h; high bioavailability (~80 %).
• Distribution: 70–80 % protein‑bound (albumin, α₁‑acid glycoprotein).
• Metabolism: Hepatic glucuronidation (UGT enzymes); hepatic CYP3A4 induction increases metabolism.
• Elimination: Primarily renal (≈ 30 % unchanged); half‑life 12–30 h (dose‑dependent, longer in the elderly).

Indications

• Partial (focal) seizures and absence seizures in epilepsy.
• Trigeminal neuralgia (painful facial neuropathy).
• Bipolar disorder – maintenance therapy for manic or mixed episodes.

Contraindications

• Absolute contraindications:
• Hypersensitivity to carbamazepine or other oxcarbazepines.
• Severe hepatic or renal impairment (dose adjustment or avoid).
• Avoid in:
• Severe anemia, thrombocytopenia (risk of aplastic anemia, agranulocytosis).
• Myelodysplastic syndromes, JAK2‑positive myeloproliferative disorders (risk of erythroleukemia).
• Pregnancy (category D; teratogenic in primates).
• Warnings:
• Drug‑induced CYP3A4 induction → reduced efficacy of oral contraceptives, warfarin, antiretrovirals.
• Potential for serotonin syndrome when combined with SSRIs, SNRIs, or MAOIs.

Dosing

• Titration: Increase 100–200 mg every 3–5 days to avoid toxic response.
• Abrupt discontinuation: Risk of status epilepticus, seizures, or withdrawal seizures; taper over 4–6 weeks.

Adverse Effects

• Common (≤ 10 %)
• Dizziness, ataxia, nausea, vomiting, headache, visual disturbances, rash.
• Serious (> 1 %)
• Severe cutaneous adverse reactions (SJS/TEN).
• Aplastic anemia, agranulocytosis, thrombocytopenia.
• Liver injury (hepatitis, cholestatic jaundice).
• Suicidal ideation; monitor mood changes.

Monitoring

• Baseline: CBC with differential, CMP, pregnancy test (female of childbearing potential).
• Periodic:
• CBC q2–4 weeks for first 3 months, then every 3 months.
• Liver function tests every 3–6 months.
• Serum carbamazepine levels: 4–12 µg/mL (therapeutic), 15–40 µg/mL (peak toxicity).
• Drug interactions: Periodic INR monitoring if on warfarin; review endocrine/adrenal axis if on steroids.

Clinical Pearls

• Induction vs. Inhibition: Carbamazepine is a strong inducer of CYP3A4, not an inhibitor; thus it can lower plasma levels of many drugs rather than increase them.
• Avoid abrupt discontinuation: Patients may experience seizure rebound. Tapering schedule should be individualised.
• Therapeutic drug monitoring: Helpful in patients with hepatic disease, renal impairment, or those on interacting drugs.
• SARS‑CoV‑2: Some reports of reduced immunogenicity with COVID‑19 vaccines; consider booster timing.
• Pregnancy: First‑trimester use linked to congenital malformations; consider alternative mood stabilizers (lithium, valproate) after risk–benefit discussion.
• Psychiatric profile: Patients may develop depression or agitation; screen at baseline and when dose changes.

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