Verapamil

Verapamil

[1 vial $1.51; 1 tablet 10 cents]

ADMINISTRATION ROUTES:

  • PO, IV

BRAND NAMES:

  • Isoptin, Isoptin SR, Verpamil 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:

  • Oral:
    Isoptin 40mg (white), 80mg (white) Isoptin SR 240mg (light green)
    Verpamil SR 120mg (white biconvex), 240mg (light green biconvex)
  • IV:
    Isoptin 5mg in 2ml solution

DOSAGE:

  • Oral: Administer in 2-3 divided doses.
    Hypertension: 240-480mg/day, 160mg maximum single dose
    Angina: 360-480mg/day
  • IV: Injection: 5mg undiluted solution slowly over 2 minutes (longer in elderly) with continuous ECG & blood pressure monitoring
    Can repeat if necessary after 5-10 minutes

DOSAGE IN RENAL FAILURE AND RENAL REPLACEMENT THERAPY:

  • No dose adjustment is required

DOSAGE IN PAEDIATRICS:

  • Oral 1-3mg/kg 8-12 hourly

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 <90mmHg) or cardiogenicshock
  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
  5. ventricular pacemaker)
  6. 5. Atrial flutter or atrial fibrillation and an accessory bypass tract (Wolff-Parkinson-White, Lown-Ganong-Levine syndromes)
  7. 6. Knownhypersensitivitytoverapamil

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; 30% of the dose should be administered to these patients.
    Verapamil decreases neuromuscular transmission in Duchenneʼs muscular dystrophy.
  • Laboratory Tests: No tests are required in addition to routine ICU blood tests
  • Drug/Laboratory Test Interactions: None known

IMPORTANT DRUG INTERACTIONS FOR THE ICU

  • Alcohol: may increase blood alcohol concentrations & prolong its effects
  • Beta-blockers: may result in additive negative effects on hear 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

  • Nervous system: CVA, confusion, insomnia, parasthesiae
  • Cardiovascular: Angina, AV dissociation
  • Digestive: Diarrhoea, dry mouth, gingival hyperplasia
  • Skin: Rash, hair loss, Stevens-Johnson syndrome, erythema multiforme
  • Urogenital: Gynaecomastia, impotence

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