Verapamil: Calcium Channel Blocker for Heart Conditions and High Blood Pressure

What is Verapamil?

Verapamil is a calcium channel blocker medication primarily used to treat high blood pressure, chest pain (angina), and certain heart rhythm disorders. It belongs to the phenylalkylamine class of calcium channel blockers and works by affecting calcium movement in heart and blood vessel cells. Verapamil has been widely prescribed since the 1980s and is available in both immediate-release and extended-release formulations.

Uses

Verapamil is approved for several cardiovascular conditions:

• High blood pressure (hypertension): Helps lower blood pressure by relaxing blood vessels and reducing the heart’s workload
• Angina pectoris: Prevents chest pain episodes by improving blood flow to the heart muscle and reducing oxygen demand
• Supraventricular tachycardia: Treats rapid heart rhythms originating above the ventricles by slowing electrical conduction
• Atrial fibrillation/flutter: Controls heart rate in patients with these irregular heart rhythms
• Hypertrophic cardiomyopathy: May help reduce symptoms in patients with this heart muscle condition

How it works

Verapamil blocks calcium channels in the heart and blood vessels, preventing calcium from entering cells. This action causes blood vessels to relax and widen, reducing blood pressure, while also slowing the heart rate and reducing the force of heart contractions. The medication particularly affects the electrical conduction system of the heart, making it especially useful for treating certain rhythm disorders.

Side effects

Common side effects include:

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• Constipation (most frequent)
• Dizziness or lightheadedness
• Headache
• Nausea
• Fatigue or weakness
• Swelling in ankles or feet
• Low blood pressure
• Slow heart rate

Serious side effects requiring immediate medical attention:

• Severe drop in blood pressure with fainting
• Heart block or very slow heart rate
• Heart failure symptoms (shortness of breath, severe swelling)
• Severe allergic reactions
• Liver problems (rare but serious)

Warnings and precautions

• Heart conditions: Should not be used in patients with certain heart blocks, severe heart failure, or very low blood pressure without careful medical supervision
• Liver function: Requires dose adjustment in patients with liver disease since verapamil is extensively metabolized by the liver
• Pregnancy and breastfeeding: Classified as pregnancy category C; should only be used when benefits outweigh risks, and passes into breast milk
• Elderly patients: May be more sensitive to blood pressure and heart rate effects, often requiring lower doses
• Sudden discontinuation: Should not be stopped abruptly as this may worsen angina or cause rebound high blood pressure

Interactions

Verapamil has numerous important drug interactions:

• Beta-blockers: Combined use can cause dangerous drops in heart rate and blood pressure
• Digoxin: Verapamil increases digoxin levels, potentially causing toxicity
• Simvastatin and other statins: Increases statin levels, raising risk of muscle damage
• Lithium: May increase lithium toxicity risk
• Grapefruit juice: Significantly increases verapamil levels and effects
• Rifampin: Reduces verapamil effectiveness by increasing its breakdown
• Cyclosporine: Verapamil increases cyclosporine levels
• Alcohol: May enhance blood pressure lowering effects

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Dosage

Verapamil dosing varies significantly based on the condition being treated and the formulation used. For immediate-release tablets, typical starting doses range from 80mg three times daily for hypertension to 120mg three times daily for angina. Extended-release formulations may start at 120-240mg once daily. Maximum doses can reach 480mg daily, though most patients respond to lower doses. Dose adjustments are made gradually, typically at weekly intervals, based on patient response and tolerance. All dosing decisions should be made by a healthcare provider who can assess individual patient factors and monitor for effectiveness and side effects.

Sources: FDA DailyMed drug labels (public domain), BNF, WHO Essential Medicines List. This article is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider before starting or stopping any medication.

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