Verapamil (Calan): Uses, Warnings, and Key Facts

What is verapamil?

Verapamil is an active ingredient used in some medicines for the treatment of supraventricular tachycardias, atrial tachycardia, high blood pressure, and angina. The ingredient is verapamil hydrochloride.

In the United States, verapamil has been marketed under brand names such as Calan, Isoptin, Calan SR, and Verelan.

How verapamil works

Verapamil works by inhibiting the entry of calcium through the membrane of heart and vascular muscle cells. This action helps explain its use in heart rhythm control, blood pressure management, and angina.

Therapeutic uses listed for verapamil

The original content lists different uses depending on the formulation and route of administration.

Oral forms

• Prophylaxis and treatment of angina, including vasospastic angina (Prinzmetal variant) and unstable angina.
• High blood pressure.
• Prophylaxis of paroxysmal supraventricular tachycardia after treatment.

Intravenous use

• Control of patients with flutter and/or chronic atrial fibrillation, except when associated with accessory conduction pathways.
• Prevention of second postinfarction of myocardium in patients without cardiac insufficiency during the acute phase.

Injectable use

• Treatment of supraventricular tachycardias.
• Treatment of atrial flutter or fibrillation, except when associated with accessory conduction pathways.

Dosage forms mentioned in the source

The source lists oral tablets or capsules in several strengths, and injectable solutions in different concentrations. The exact dose depends on the product, the route, the condition being treated, and individual clinical factors.

Because dosing is highly specific, readers should verify the prescribed strength and instructions on the official label or medication guide.

Contraindications listed in the source

The original content lists the following situations where verapamil should not be used, depending on the formulation:

• Hypersensitivity.
• Cardiogenic shock.
• Sinus disease, except with an implanted pacemaker.
• Second- or third-degree AV block, except with an implanted pacemaker.
• Atrial flutter or atrial fibrillation with an accessory AV conduction pathway.
• For oral forms: left-sided heart failure and hypotension.
• For injectable forms: severe hypotension, severe CHF, ventricular tachycardia except verapamil-sensitive types, acute myocardial infarction, and use with beta-adrenergic blockers.

Warnings and precautions

• Dose adjustment may be needed in liver failure and kidney failure.
• Patients with heart failure or depressed ventricular function should be compensated before treatment, according to the source.
• Decreased neuromuscular transmission is noted as a precaution, including in Duchenne syndrome.
• For oral use, the source mentions caution in acute myocardial infarction.
• For parenteral use, monitoring is mentioned in Duchenne muscular dystrophy and with supratentorial tumors.

Interactions with verapamil

The source lists several important interaction groups. This is one reason the official medication guide and pharmacist review are important.

• Plasma levels may increase with CYP3A4 inhibitors and ritonavir.
• Plasma levels may decrease with CYP3A4 inducers.
• Cardiovascular effects may be mutually potentiated with antiarrhythmics and beta-blockers.
• Hypotensive effects may be enhanced with antihypertensives, diuretics, and vasodilators.
• Additive hypotensive effect is listed with prazosin and terazosin.
• Toxicity of lithium may increase.
• Bleeding tendency may increase with AAS.
• Plasma levels of ethanol and carbamazepine may increase.
• Activity of neuromuscular blocking agents may be increased.
• Hypotensive effect may be decreased by rifampicin and sulfinpyrazone.
• Caution is advised with atorvastatin, simvastatin, lovastatin, drugs that bind to plasma proteins, and inhalation anesthetics.

Pregnancy and breastfeeding

The source states that safety in pregnancy has not been established and that use is not especially recommended in the first trimester.

For breastfeeding, the source advises avoiding verapamil because it is partly eliminated in milk.

Driving and machinery

Verapamil may sometimes reduce the ability to drive or operate dangerous machinery. This may be more likely at the beginning of treatment, when the dose is increased, when switching from another medicine, or when alcohol is used.

Adverse reactions and side effects listed in the source

• Dizziness.
• Headache.
• Bradycardia.
• Hypotension.

Frequently asked questions

Sources and reference points

This article was rewritten from the supplied content and aligned with the FDA/USP-based ingredient information referenced in the original source. For the most accurate product-specific details, consult the official medication guide and package labeling.