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Tablet $0.06, Vial $5.17

Verapamil

Editor: AP Updated Class: Antiarrhythmic

ADMINISTRATION ROUTES:

PO, IV

ALTERNATIVE NAMES:

Isoptin, Isoptin SR, Verapamil SR

ICU INDICATIONS:

  1. Tachycardias including paroxysmal SVT, AF with rapid ventricular response (excluding WPW syndrome), atrial flutter with rapid ventricular response, extrasystoles
  2. Hypertension
  3. Acute coronary insufficiency

PRESENTATION AND ADMINISTRATION:

PO

  • Isoptin 40 mg (white), 80 mg (white)
  • Isoptin SR 240 mg (light green)
  • Verpamil SR 120 mg (white biconvex), 240 mg (light green biconvex)

IV

  • Isoptin 5mg in 2 mL solution

DOSAGE:

PO:

Hypertension:

240 - 480 mg/day in 2 - 3 divided doses

160 mg maximum single dose

Angina:

360 - 480 mg/day in 2 - 3 divided doses

IV:

5 mg undiluted solution slow push over 2 mins

Patients must have continuous ECG & blood pressure monitoring. Give more slowly in elderly patients. Can repeat if necessary after 5 - 10 mins

DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:

No dose adjustment is required

DOSAGE IN PAEDIATRICS:

PO:

1 - 3 mg/kg every 8 - 12 hours

CLINICAL PHARMACOLOGY:

Verapamil is a calcium ion influx inhibitor. It decreases the influx of ionic calcium across the cell membrane of arterial smooth muscle as well as conductile & contractile myocardial cells. It dilates the main coronary arteries & inhibits coronary artery spasm. It also reduces afterload so reducing myocardial energy consumption. By decreasing calcium influx through the slow channels of the AV node, the effective refractory period is increased so AV conduction is slowed in a rate-related manner. It has no effect on the normal atrial action potential or intraventricular conduction time.

CONTRAINDICATIONS:

  1. Severe LV dysfunction
  2. Hypotension (systolic < 90 mmHg) or cardiogenic shock
  3. Sick sinus syndrome (except in patients with a functioning external ventricular pacemaker)
  4. Second- or third-degree AV block (except in patients with a functioning external ventricular pacemaker)
  5. Atrial flutter or atrial fibrillation and an accessory bypass tract (Wolff-Parkinson- White, Lown-Ganong-Levine syndromes)
  6. Known hypersensitivity to verapamil

WARNINGS:

The negatively inotropic effects of verapamil are mostly compensated for by its afterload reduction without a net impairment of LV performance. It should be used in caution with patients with severe LV dysfunction (LVEF < 30%), moderate to severe symptoms of cardiac failure, and in any patients with dysfunction also receiving beta-blockers.

Very rapid ventricular responses or VF have been described in patients with coexisting accessory AV pathways that may not become apparent until the administration of verapamil. First-degree AV block with transient bradycardia may be seen, sometimes accompanied by nodal escape rhythms. PR-interval prolongation corresponds with verapamil plasma concentrations. Serious adverse effects (including death) have been recorded in a series of patients with hypertrophic cardiomyopathy receiving verapamil. Elevation of liver enzymes have been reported.

PRECAUTIONS:

General:

Severe liver dysfunction prolongs elimination half-life. Only 30% of the dose should be administered to these patients. Verapamil decreases neuromuscular transmission in Duchenne's muscular dystrophy.

Laboratory Tests:

No tests are required in addition to routine ICU blood tests

Drug/Laboratory Test Interactions:

None known

IMPORTANT DRUG INTERACTIONS IN ICU:

Alcohol: May increase blood alcohol concentrations & prolong its effects

Beta-blockers: May result in additive negative effects on heart rate, AV conduction & cardiac contractility.

Digoxin: Chronic verapamil usage can increase serum digoxin levels by 50-75% during first week of therapy. Effects exaggerated in hepatic cirrhosis.

Disopyramide: Should not be given within 48 hours before or 24 hours after verapamil

Lithium: Increased sensitivity to the effects of lithium (neurotoxicity) reported

Carbamazepine: Levels may be increased by verapamil

Rifampicin: Markedly reduces oral verapamil bioavailability

Cyclosporin: Levels may be increased by verapamil

Theophylline: Levels may be increased by verapamil

Neuromuscular blocking agents: Verapamil may prolong the duration of action

ADVERSE REACTIONS:

Neurological:

CVA, confusion, insomnia, paraesthesiae

Cardiovascular:

Angina, AV dissociation

Digestive:

Diarrhoea, dry mouth, gingival hyperplasia

Dermatological:

Rash, hair loss, Stevens-Johnson syndrome, erythema multiforme

Urogenital:

Gynaecomastia, impotence