warnings and cautions
5 WARNINGS AND PRECAUTIONS Congestive heart failure or pulmonary edema may develop ( 5.1 ) Hypotension/dizziness may occur ( 5.2 ) Elevated transaminases have occurred; monitor liver function ( 5.3 ) Ventricular fibrillation has occurred in patients with atrial flutter or atrial fibrillation and an accessory bypass tract ( 5.4 ) Reduce dose or discontinue therapy if marked first-degree AV block or progression to second- or third-degree AV block occurs ( 5.5 ) Sinus bradycardia, pulmonary edema, severe hypotension, second-degree AV block, sinus arrest, and death occurred in patients with hypertrophic cardiomyopathy ( 5.6 ) 5.1 Heart Failure Verapamil has a negative inotropic effect which, in most patients, is compensated by its afterload reduction (decreased systemic vascular resistance) properties without a net impairment of ventricular performance. In previous clinical experience with 4,954 patients primarily with immediate-release verapamil, 87 (1.8%) developed congestive heart failure or pulmonary edema. Avoid verapamil in patients with severe left ventricular dysfunction (e.g., ejection fraction less than 30% or moderate to severe symptoms of cardiac failure) and in patients with any degree of ventricular dysfunction if they are receiving a beta-adrenergic blocker [see Drug Interactions ( 7.4 )]. Control patients with milder ventricular dysfunction, if possible, with optimum doses of digitalis and/or diuretics before verapamil treatment is started [see Drug Interactions ( 7.5 )] . 5.2 Hypotension Occasionally, the pharmacologic action of verapamil may produce a decrease in blood pressure below normal levels which may result in dizziness or symptomatic hypotension. In hypertensive patients, decreases in blood pressure below normal are unusual. The incidence of hypotension observed in 4,954 patients enrolled in clinical trials of other verapamil formulations was 2.5% [see Adverse Reactions ( 6.1 )] . In clinical studies of Verapamil Hydrochloride Extended-release Capsules (PM), 1.7% of the patients developed significant hypotension. Tilt table testing (60 degrees) was not able to induce orthostatic hypotension. 5.3 Elevated Liver Enzymes Elevations of transaminases with and without concomitant elevations in alkaline phosphatase and bilirubin have been reported. Such elevations have sometimes been transient and may disappear even in the face of continued verapamil treatment. Several cases of hepatocellular injury related to verapamil have been proven by rechallenge; half of these had clinical symptoms (malaise, fever, and/or right upper quadrant pain) in addition to elevations of SGOT, SGPT, and alkaline phosphatase. Periodic monitoring of liver function in patients receiving verapamil is therefore prudent. 5.4 Accessory Bypass Tract (Wolff-Parkinson-White or Lown-Ganong-Levine) Some patients with paroxysmal and/or chronic atrial flutter or atrial fibrillation and a coexisting accessory AV pathway have developed increased antegrade conduction across the accessory pathway bypassing the AV node, producing a very rapid ventricular response or ventricular fibrillation after receiving intravenous verapamil (or digitalis). Although a risk of this occurring with oral verapamil has not been established, such patients receiving oral verapamil may be at risk and its use in these patients is contraindicated [see Contraindications (4) ]. Treatment is usually DC-cardioversion. Cardioversion has been used safely and effectively after oral verapamil. 5.5 Atrioventricular Block The effect of verapamil on AV conduction and the SA node may lead to asymptomatic first-degree AV block and transient bradycardia, sometimes accompanied by nodal escape rhythms. PR interval prolongation is correlated with verapamil plasma concentrations, especially during the early titration phase of therapy. Higher degrees of AV block, however, were infrequently (0.8%) observed in previous verapamil clinical trials [see Adverse Reactions ( 6.1 )]. Marked first-degree block or progressive development to second- or third-degree AV block requires a reduction in dosage or, in rare instances, discontinuation of verapamil and institution of appropriate therapy depending upon the clinical situation. 5.6 Patients with Hypertrophic Cardiomyopathy In 120 patients with hypertrophic cardiomyopathy, idiopathic hypertrophic subaortic stenosis (IHSS) (most of them refractory or intolerant to propranolol) who received therapy with verapamil at doses up to 720 mg/day, a variety of serious adverse effects were seen. Three patients died in pulmonary edema; all had severe left ventricular outflow obstruction and a history of left ventricular dysfunction. Eight other patients had pulmonary edema and/or severe hypotension; abnormally high (over 20 mm Hg) pulmonary capillary wedge pressure and a marked left ventricular outflow obstruction were present in most of these patients. Concomitant administration of quinidine [see Drug Interactions ( 7.10 )] preceded the severe hypotension in 3 of the 8 patients (2 of whom developed pulmonary edema). Sinus bradycardia occurred in 11% of the patients, second-degree AV block in 4% and sinus arrest in 2% [see Adverse Reactions (6) ]. It must be appreciated that this group of patients had a serious disease with a high mortality rate. Most adverse effects responded well to dose reduction and only rarely did verapamil have to be discontinued.