WARNINGS
VERAPAMIL HYDROCHLORIDE SHOULD BE GIVEN AS A SLOW
INTRAVENOUS INJECTION OVER AT LEAST A TWO-MINUTE PERIOD OF TIME (see DOSAGE AND
ADMINISTRATION).
Hypotension
Verapamil hydrochloride injection often produces a
decrease in blood pressure below baseline levels that is usually transient and
asymptomatic but may result in dizziness. Systolic pressure less than 90 mm Hg
and/or diastolic pressure less than 60 mm Hg was seen in 5% to 10% of patients
in controlled U.S. trials in supraventricular tachycardia and in about 10% of
the patients with atrial flutter/fibrillation. The incidence of symptomatic
hypotension observed in studies conducted in the U.S. was approximately 1.5%.
Three of the five symptomatic patients required intravenous pharmacologic treatment
(norepinephrine bitartrate, metaraminol bitartrate, or 10% calcium gluconate).
All recovered without sequelae.
Extreme Bradycardia/Asystole
Verapamil hydrochloride affects the AV and SA nodes and
rarely may produce second- or third-degree AV block, bradycardia, and, in
extreme cases, asystole. This is more likely to occur in patients with a sick
sinus syndrome (SA nodal disease), which is more common in older patients.
Bradycardia associated with sick sinus syndrome was reported in 0.3% of the
patients treated in controlled double-blind trials in the U.S. The total
incidence of bradycardia (ventricular rate less than 60 beats/min) was 1.2% in
these studies. Asystole in patients other than those with sick sinus syndrome
is usually of short duration (few seconds or less), with spontaneous return to
AV nodal or normal sinus rhythm. If this does not occur promptly, appropriate
treatment should be initiated immediately. (See ADVERSE REACTIONS and Suggested
Treatment of Acute Cardiovascular Adverse Reactions.)
Heart Failure
When heart failure is not severe or rate related, it
should be controlled with digitalis glycosides and diuretics, as appropriate,
before verapamil is used. 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.
Concomitant Antiarrhythmic Therapy
Digitalis: Verapamil hydrochloride injection has
been used concomitantly with digitalis preparations without the occurrence of
serious adverse effects. However, since both drugs slow AV conduction, patients
should be monitored for AV block or excessive bradycardia.
Procainamide: Verapamil hydrochloride injection
has been administered to a small number of patients receiving oral procainamide
without the occurrence of serious adverse effects.
Quinidine: Verapamil hydrochloride injection has
been administered to a small number of patients receiving oral quinidine
without the occurrence of serious adverse effects. However, three patients have
been described in whom the combination resulted in an exaggerated hypotensive
response presumably from the combined ability of both drugs to antagonize the
effects of catecholamines on α-adrenergic receptors. Caution should
therefore be used when employing this combination of drugs.
Beta-Adrenergic Blocking Drugs: Verapamil
hydrochloride injection has been administered to patients receiving oral
beta-blockers without the development of serious adverse effects. However,
since both drugs may depress myocardial contractility and AV conduction, the
possibility of detrimental interactions should be considered. The concomitant
administration of intravenous beta-blockers and intravenous verapamil has
resulted in serious adverse reactions (see CONTRAINDICATIONS), especially
in patients with severe cardiomyopathy, congestive heart failure, or recent
myocardial infarction.
Disopyramide: Until data on possible interactions
between verapamil and all forms of disopyramide phosphate are obtained,
disopyramide should not be administered within 48 hours before or 24 hours after
verapamil administration.
Flecainide: A study in healthy volunteers showed
that the concomitant administration of flecainide and verapamil may have
additive effects reducing myocardial contractility, prolonging AV conduction,
and prolonging repolarization.
Heart Block: Verapamil prolongs AV conduction
time. While high-degree AV block has not been observed in controlled clinical
trials in the United States, a low percentage (less than 0.5%) has been reported
in the world literature. Development of second- or third-degree AV block or
unifascicular, bifascicular, or trifascicular bundle branch block requires
reduction in subsequent doses or discontinuation of verapamil and institution
of appropriate therapy, if needed. (See ADVERSE REACTIONS, Suggested
Treatment of Acute Cardiovascular Adverse Reactions.)
Hepatic and Renal Failure: Significant hepatic and
renal failure should not increase the effects of a single intravenous dose of
verapamil hydrochloride but may prolong its duration. Repeated injections of verapamil
hydrochloride injection in such patients may lead to accumulation and an
excessive pharmacologic effect of the drug. There is no experience to guide use
of multiple doses in such patients, and this generally should be avoided. If
repeated injections are essential, blood pressure and PR interval should be
closely monitored and smaller repeat doses should be utilized.
Verapamil cannot be removed by hemodialysis.
Premature Ventricular Contractions: During
conversion to normal sinus rhythm, or marked reduction in ventricular rate, a
few benign complexes of unusual appearance (sometimes resembling premature ventricular
contractions) may be seen after treatment with verapamil hydrochloride. Similar
complexes are seen during spontaneous conversion of supraventricular
tachycardias, after D.C.-cardioversion and other pharmacologic therapy. These
complexes appear to have no clinical significance.
Duchenne's Muscular Dystrophy: Verapamil
hydrochloride injection can precipitate respiratory muscle failure in these
patients and should, therefore, be used with caution.
Increased Intracranial Pressure: Verapamil
hydrochloride injection has been seen to increase intracranial pressure in
patients with supratentorial tumors at the time of anesthesia induction.
Caution should be taken and appropriate monitoring performed.