Calcium channel blockers · Cardiovascular
Verapamil
Isoptin®(brand names vary by market)
The most cardiac of the calcium channel blockers, and the most constipating.
Also: modified release, injection
Mechanism
Non-dihydropyridine calcium channel blocker with the strongest negative inotropic and AV-nodal effects of the class.
Indications
- Rate control in supraventricular arrhythmia
- Angina
- Hypertension
- Cluster headache prophylaxis
Formulations
Dosing concepts
Heart failure
The negative inotropy is the strongest in the class; in reduced ejection fraction it is contraindicated rather than merely cautioned.
With digoxin
It raises digoxin concentrations, so an existing digoxin dose is reviewed rather than left alone.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~20 to 35% (extensive first-pass)
- Half-life
- 3 to 7 h, longer with chronic dosing
- Elimination
- hepatic: CYP3A4 substrate and inhibitor, more potent than diltiazem
- Protein binding
- ~90%
Adverse effects
- ConstipationcommonAffects a large minority and is the usual reason it is abandoned.
- Bradycardia and AV blockcommon & serious
- Worsening heart failureserious
- Peripheral oedemacommon
- Gingival hyperplasiacommon
Contraindications & precautions
Contraindications
- Heart failure with reduced ejection fraction
- High-grade AV block
- Atrial fibrillation with pre-excitation
- Concurrent intravenous beta blockade
Precautions
- Concurrent beta blockade
- Hepatic impairment
- Older adults, in whom constipation can become obstruction
Interactions
- Beta blockers + Verapamil / diltiazemcautionBradycardia, AV block, hypotension, occasionally pacing-level.
- Amlodipine / felodipine + Strong CYP3A4 inhibitors; grapefruit (felodipine)monitorMore vasodilation: flushing, edema, hypotension.
- Simvastatin / atorvastatin + Clarithromycin, itraconazole, ritonavir (strong CYP3A4 inhibitors)avoidMyopathy up to rhabdomyolysis: muscle pain, dark urine, AKI.
Monitoring
Heart rate, blood pressure, PR interval
Dose-dependent conduction effects
Bowel function
The commonest tolerability failure, and preventable if anticipated
Digoxin level if co-prescribed
Verapamil raises it
Counselling points
- Swallow modified-release forms whole.
- Constipation is very common: start fluids and fibre early rather than waiting for it.
- Avoid grapefruit juice.
- Report fainting or a very slow pulse.
Clinical pearls
- Giving intravenous verapamil to a wide-complex tachycardia that turns out to be ventricular is a classic and sometimes fatal error. Wide and fast is treated as ventricular until proven otherwise.
- In atrial fibrillation with pre-excitation, blocking the AV node pushes conduction down the accessory pathway and can precipitate ventricular fibrillation.
References & review
- Verapamil product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.