Major
Carbamazepine × Warfarin
Antiepileptics. Carboxamide derivatives×Vitamin K antagonist anticoagulants
Mechanism
Carbamazepine strongly induces CYP2C9 and CYP3A4. Warfarin plasma levels fall by 50–70% over 2–4 weeks; anticoagulant effect weakens.
Symptoms
INR drops below target. Thromboembolic risk rises: deep vein thrombosis, pulmonary embolism, ischaemic stroke in atrial fibrillation.
Management
After starting carbamazepine, check INR every 1–2 weeks for the first month and titrate warfarin (usually 1.5- to 2-fold dose increase). On carbamazepine withdrawal, induction persists for 2–4 weeks – return warfarin gradually. Alternative anticonvulsants without induction: levetiracetam, lamotrigine.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.