Verapamil Hydrochloride

VERAPAMIL HYDROCHLORIDE- verapamil hydrochloride injection, solution
Hospira, Inc.

Fliptop Vial

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Rx only

DESCRIPTION

Verapamil hydrochloride is a calcium antagonist or slow-channel inhibitor. Verapamil Hydrochloride Injection, USP is a sterile, nonpyrogenic solution containing verapamil hydrochloride 2.5 mg/mL and sodium chloride 8.5 mg/mL in water for injection. The solution contains no bacteriostat or antimicrobial agent and is intended for single-dose intravenous administration. May contain hydrochloric acid for pH adjustment; pH is 4.0 to 6.5.

The chemical name of Verapamil Hydrochloride, USP is benzeneacetonitrile, α-[3-[{2-(3,4-dimethoxyphenyl)ethyl} methylamino] propyl]-3,4-dimethoxy-α-(1-methylethyl) hydrochloride. Verapamil hydrochloride is a white or practically white crystalline powder. It is practically odorless and has a bitter taste. It is soluble in water; freely soluble in chloroform; sparingly soluble in alcohol; practically insoluble in ether. It has the following structural formula:

Chemical Structure
(click image for full-size original)

Molecular weight: 491.07

Molecular formula: C27 H38 N2 O4 ∙ HCl

Verapamil hydrochloride is not chemically related to other antiarrhythmic drugs.

CLINICAL PHARMACOLOGY

Mechanism of Action

Verapamil inhibits the calcium ion (and possibly sodium ion) influx through slow channels into conductile and contractile myocardial cells and vascular smooth muscle cells. The antiarrhythmic effect of verapamil appears to be due to its effect on the slow channel in cells of the cardiac conduction system. The vasodilatory effect of verapamil appears to be due to its effect on blockade of calcium channels as well as α receptors.

In the isolated rabbit heart, concentrations of verapamil that markedly affect SA nodal fibers or fibers in the upper and middle regions of the AV node have very little effect on fibers in the lower AV node (NH region) and no effect on atrial action potentials or His bundle fibers.

Electrical activity in the SA and AV nodes depends, to a large degree, upon calcium influx through the slow channel. By inhibiting this influx, verapamil slows AV conduction and prolongs the effective refractory period within the AV node in a rate-related manner. This effect results in a reduction of the ventricular rate in patients with atrial flutter and/or atrial fibrillation and a rapid ventricular response.

By interrupting reentry at the AV node, verapamil can restore normal sinus rhythm in patients with paroxysmal supraventricular tachycardias (PSVT), including PSVT associated with Wolff-Parkinson-White syndrome.

Verapamil does not induce peripheral arterial spasm.

Verapamil has a local anesthetic action that is 1.6 times that of procaine on an equimolar basis. It is not known whether this action is important at the doses used in man.

Verapamil does not alter total serum calcium levels.

Hemodynamics

Verapamil reduces afterload and myocardial contractility. The commonly used intravenous doses of 5 to 10 mg verapamil hydrochloride produce transient, usually asymptomatic, reduction in normal systemic arterial pressure, systemic vascular resistance and contractility; left ventricular filling pressure is slightly increased. In most patients, including those with organic cardiac disease, the negative inotropic action of verapamil is countered by reduction of afterload, and cardiac index is usually not reduced. However, in patients with moderately severe to severe cardiac dysfunction (pulmonary wedge pressure above 20 mm Hg, ejection fraction less than 30%), acute worsening of heart failure may be seen. Peak therapeutic effects occur within 3 to 5 minutes after a bolus injection.

Pharmacokinetics

Intravenously administered verapamil hydrochloride has been shown to be rapidly metabolized. Following intravenous infusion in man, verapamil is eliminated bi-exponentially, with a rapid early distribution phase (half-life about 4 minutes) and a slower terminal elimination phase (half-life 2 to 5 hours). In healthy men, orally administered verapamil hydrochloride undergoes extensive metabolism in the liver, with 12 metabolites having been identified, most in only trace amounts. The major metabolites have been identified as various N- and O-dealkylated products of verapamil. Approximately 70% of an administered dose is excreted in the urine and 16% more in the feces within 5 days. About 3% to 4% is excreted as unchanged drug.

Aging may affect the pharmacokinetics of verapamil given to hypertensive patients. Elimination half-life may be prolonged in the elderly.

INDICATIONS AND USAGE

Verapamil Hydrochloride Injection, USP is indicated for the following:

  • Rapid conversion to sinus rhythm of paroxysmal supraventricular tachycardias, including those associated with accessory bypass tracts (Wolff-Parkinson-White [W-P-W] and Lown-Ganong-Levine [L-G-L] syndromes). When clinically advisable, appropriate vagal maneuvers (e.g., Valsalva maneuver) should be attempted prior to verapamil hydrochloride administration.
  • Temporary control of rapid ventricular rate in atrial flutter or atrial fibrillation except when the atrial flutter and/or atrial fibrillation are associated with accessory bypass tracts (Wolff-Parkinson-White (W-P-W) and Lown-Ganong-Levine (L-G-L) syndromes).

In controlled studies in the United States, about 60% of patients with supraventricular tachycardia converted to normal sinus rhythm within 10 minutes after intravenous verapamil hydrochloride. Uncontrolled studies reported in the world literature describe a conversion rate of about 80%. About 70% of patients with atrial flutter and/or fibrillation with a faster ventricular rate respond with a decrease in ventricular rate of at least 20%. Conversion of atrial flutter or fibrillation to sinus rhythm is uncommon (about 10%) after verapamil hydrochloride and may reflect the spontaneous conversion rate, since the conversion rate after placebo was similar. Slowing of the ventricular rate in patients with atrial fibrillation/flutter lasts 30 to 60 minutes after a single injection.

Because a small fraction (<1%) of patients treated with verapamil hydrochloride respond with life-threatening adverse responses (rapid ventricular rate in atrial flutter/fibrillation, and an accessory bypass tract, marked hypotension, or extreme bradycardia/asystole – see CONTRAINDICATIONS and WARNINGS), the initial use of verapamil hydrochloride injection should, if possible, be in a treatment setting with monitoring and resuscitation facilities, including D.C.-cardioversion capability (see ADVERSE REACTIONS, Suggested Treatment of Acute Cardiovascular Adverse Reactions). As familiarity with the patient’s response is gained, use in an office setting may be acceptable.

Cardioversion has been used safely and effectively after verapamil hydrochloride injection.

CONTRAINDICATIONS

Verapamil hydrochloride injection is contraindicated in:

  1. Severe hypotension or cardiogenic shock.
  2. Second- or third-degree AV block (except in patients with a functioning artificial ventricular pacemaker).
  3. Sick sinus syndrome (except in patients with a functioning artificial ventricular pacemaker).
  4. Severe congestive heart failure (unless secondary to a supraventricular tachycardia amenable to verapamil therapy).
  5. Patients receiving intravenous beta-adrenergic blocking drugs (e.g., propranolol). Intravenous verapamil and intravenous beta-adrenergic blocking drugs should not be administered in close proximity to each other (within a few hours), since both may have a depressant effect on myocardial contractility and AV conduction.
  6. Patients with atrial flutter or atrial fibrillation and an accessory bypass tract (e.g., Wolff-Parkinson-White, Lown-Ganong-Levine syndromes) are at risk to develop ventricular tachyarrhythmia including ventricular fibrillation if verapamil is administered. Therefore, the use of verapamil in these patients is contraindicated.
  7. Ventricular tachycardia: Administration of intravenous verapamil to patients with wide-complex ventricular tachycardia (QRS ≥ 0.12 sec) can result in marked hemodynamic deterioration and ventricular fibrillation. Proper pretherapy diagnosis and differentiation from wide-complex supraventricular tachycardia is imperative in the emergency room setting.
  8. Known hypersensitivity to verapamil hydrochloride.

WARNINGS

VERAPAMIL HYDROCHLORIDE SHOULD BE GIVEN AS A SLOW INTRAVENOUS INJECTION OVER AT LEAST A TWO-MINUTE PERIOD OF TIME (see DOSAGE AND ADMINISTRATION).

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