Section 02 · Monograph
Verapamil
Reviewed Nov 2026FDA label
Calan / IsoptinCalcium channel blocker
- Forms
- IR tab: 40, 80, 120mg | SR tab: 120, 180, 240mg | ER cap: 100-360mg
- Dose
- Cluster prevention: 240-480mg/day divided (ECG monitoring with dose increases)
- MOA
- L-type Ca2+ channel blockade
Indications
- Hypertension, angina, supraventricular tachyarrhythmiasFDA-labeled
Off-Label Uses
- Cluster headache prophylaxis (first-line)Off-label
- Migraine prophylaxis (limited evidence)Off-label
Mechanism of Action
- Non-dihydropyridine L-type calcium channel blocker; mechanism in cluster headache is thought to involve hypothalamic and trigeminovascular effects
Full Dosing
Adult / usual
- Cluster prophylaxis: typically 240mg/day, increase by 80mg every 1-2 weeks as tolerated to about 480mg/day; higher doses (720-960mg/day) only under specialist supervision with ECG monitoring
- ECG (PR interval) at baseline and after each dose increase
- Use sustained-release formulations to improve tolerability
Contraindications
- Severe left ventricular dysfunction, hypotension or cardiogenic shock
- Sick sinus syndrome or second/third-degree AV block (without pacemaker)
- Atrial flutter/fibrillation with an accessory bypass tract (WPW)
- Hypersensitivity
Drug Interactions
- Strong CYP3A4 inhibitors raise verapamil levels
- CYP3A4 inducers (carbamazepine, phenytoin) lower levels; verapamil raises carbamazepine levels
- Beta-blockers and digoxin: bradycardia and AV block
- Simvastatin and atorvastatin: increased myopathy risk
- Lithium neurotoxicity
Adverse Effects
- Constipation (common)
- Hypotension, edema, bradycardia, AV block
- Dizziness, headache
- Gingival hyperplasia (rare)
Monitoring Parameters
- ECG, heart rate and blood pressure
- Liver tests occasionally
Pregnancy & Lactation
- Crosses the placenta; limited data
- Present in milk