ModerateAntiepileptics. Carboxamide derivatives×Non-dihydropyridine calcium channel blocker
Updated · Methodology
Mechanism
Verapamil inhibits CYP3A4, the main enzyme of carbamazepine metabolism (verapamil and carbamazepine labels). In patients with epilepsy, carbamazepine AUC rose by 46%, which can cause its side effects (verapamil label). The reverse effect is also possible: carbamazepine is a potent CYP3A4 inducer (carbamazepine label), and CYP3A4 inducers lower verapamil levels (verapamil labels).
Symptoms
Double vision, headache, ataxia, dizziness, drowsiness and nausea (verapamil and carbamazepine labels). Severe cases: cardiac conduction disorders and atrioventricular (AV) block (carbamazepine label).
Management
The combination is allowed but is managed by carbamazepine levels. After verapamil is added, measure the blood carbamazepine level and adjust its dose if needed (carbamazepine label). The usual adult therapeutic range of carbamazepine is 4–12 mcg/mL (FDA carbamazepine label). Warn the patient about signs of carbamazepine excess: double vision, headache, unsteady gait and dizziness (verapamil labels). Also monitor the effect of verapamil, because CYP3A4 inducers lower its levels (verapamil label).
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.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- FDA: Tegretol / Tegretol-XR (carbamazepine) prescribing information (2026)– FDA label, DailyMed setid 8d409411-aa9f-4f3a-a52c-fbcb0c3ec053, PRECAUTIONS, Drug Interactions
- AEMPS: Ficha técnica: Carbamazepina (nº registro 39955), secciones 4.3 y 4.5 (2026)– AEMPS, CIMA, nº registro 39955, revisión 09/2026, secciones 4.3 y 4.5
- AEMPS: Ficha técnica: Verapamilo (nº registro 50891), secciones 4.4 y 4.5 (2024)– AEMPS, CIMA, nº registro 50891, revisión 06/2024, secciones 4.4 y 4.5
- FDA: Verapamil hydrochloride extended-release tablets (verapamil) prescribing information (2025)– FDA label, Glenmark Pharmaceuticals Inc., USA, DailyMed setid ba1bf1ae-9347-4d17-998b-14bf7b5984ce, revised 12/2025, Warnings: Heart failure, Atrioventricular block; Precautions: Drug interactions (Beta-blockers, Carbamazepine, Cytochrome inducers/inhibitors)