Isoptin Sr (Verapamil Hydrochloride)

Isoptin Sr (verapamil) is indicated for cardiovascular conditions that involve abnormal calcium influx.

• Hypertension: reduces systolic and diastolic blood pressure by causing arterial vasodilation.
• Angina pectoris: alleviates chest pain by decreasing myocardial oxygen demand and improving coronary blood flow.
• Supraventricular tachycardia: slows atrioventricular nodal conduction to restore normal heart rhythm in atrial fibrillation or flutter.

• Verapamil blocks L‑type calcium channels in cardiac and smooth‑muscle cells, limiting calcium entry during depolarisation. This reduces myocardial contractility, slows conduction through the atrioventricular node, and promotes vasodilation of coronary and peripheral vessels, thereby lowering blood pressure and relieving angina. The phenylalkylamine binding profile gives it greater effect on cardiac tissue than on vascular smooth muscle.

Verapamil may cause a range of adverse reactions, varying from mild to serious.

Common Side Effects

• Constipation: reduced gastrointestinal motility.
• Dizziness or light‑headedness: related to blood pressure lowering.
• Headache: often transient.
• Peripheral edema: mild swelling of ankles or feet.

Serious or Rare Side Effects

• Bradycardia: abnormally slow heart rate.
• Heart block: impairment of electrical conduction between atria and ventricles.
• Severe hypotension: marked drop in blood pressure that may cause fainting.

When prescribing Verapamil, clinicians should consider several safety measures.

• Cardiac function assessment: evaluate for existing heart block or severe left ventricular dysfunction before initiating therapy.
• Concomitant beta‑blocker use: avoid combined use unless closely monitored due to risk of excessive bradycardia.
• Liver impairment: dose may need adjustment in patients with hepatic dysfunction.
• Pregnancy and lactation: use only if potential benefit justifies potential risk, as safety data are limited.
• Drug‑induced arrhythmias: monitor ECG for new conduction abnormalities during treatment.
• Store at ambient temperature: keep below 25 °C, in the original container, protected from moisture and light.

Verapamil interacts with several medicines that can alter its plasma concentration or cardiac effects.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): can markedly increase verapamil levels, risking toxicity.
• Digoxin: concurrent use may raise digoxin concentrations and precipitate arrhythmias.

Moderate Interactions (Monitor Closely)

• Beta‑blockers (e.g., metoprolol): may enhance bradycardic and hypotensive effects.
• Antihypertensive diuretics: can potentiate blood pressure lowering, requiring dose adjustments.
• Statins metabolised by CYP3A4 (e.g., simvastatin): may increase statin exposure, raising risk of myopathy.