VERAPAMIL Drug Interactions: What You Need to Know

INTERACTIONS CYP3A4 inhibitors increase verapamil levels ( 7.1 ) CYP3A4 inducers decrease verapamil levels ( 7.1 ) If simvastatin is co-administered with verapamil, do not exceed doses greater than 10 mg daily of simvastatin ( 7.2 ) If lovastatin is co-administered with verapamil, do not exceed doses greater than 40 mg daily of lovastatin ( 7.2 ) Grapefruit juice may significantly increase verapamil levels ( 7.3 ) Beta blockers: reports of excess bradycardia and AV block, including complete heart block; monitor closely ( 7.4 ) Digoxin levels can increase by 50 to 75%; reduce digoxin dose ( 7.5 ) Alcohol elimination inhibited resulting in elevated ethanol levels ( 7.6 )

7.1 CYP3A4 Inhibitors and Inducers In vitro metabolic studies indicate that verapamil is metabolized by cytochrome P450, CYP3A4, CYP1A2, and CYP2C. Clinically significant interactions have been reported with inhibitors of CYP3A4 (e.g., erythromycin, ritonavir) causing elevation of plasma levels of verapamil. Hypotension, bradyarrhythmias, and lactic acidosis have been observed in patients receiving concurrent telithromycin, an antibiotic in the ketolide class of antibiotics. Inducers of CYP3A4 (e.g., rifampin) have caused a lowering of plasma levels of verapamil.

Ivabradine

Concurrent use of verapamil increases exposure to ivabradine and may exacerbate bradycardia and conductions disturbances. Avoid concomitant use of ivabradine and verapamil.

7.2 HMG-CoA Reductase Inhibitors The use of HMG-CoA reductase inhibitors that are CYP3A4 substrates in combination with verapamil has been associated with reports of myopathy/rhabdomyolysis. Co-administration of multiple doses of 10 mg of verapamil with 80 mg simvastatin resulted in exposure to simvastatin 2.5-fold that following simvastatin alone. Limit the dose of simvastatin in patients on verapamil to 10 mg daily. Limit the daily dose of lovastatin to 40 mg. Lower starting and maintenance doses of other CYP3A4 substrates (e.g., atorvastatin) may be required as verapamil may increase the plasma concentration of these drugs.

7.3 Grapefruit Juice Grapefruit juice may significantly increase concentrations of verapamil. Grapefruit juice given to nine healthy volunteers increased S- and R- verapamil AUC 0-12 by 36% and 28%, respectively. Steady state C max and C min of S-verapamil increased by 57% and 16.7%, respectively with grapefruit juice compared to control. Similarly, C max and C min of R-verapamil increased by 40% and 13%, respectively. Grapefruit juice did not affect half-life, nor was there a significant change in AUC 0-12 ratio R/S compared to control. Grapefruit juice did not cause a significant difference in the pharmacokinetics of norverapamil. This increase in verapamil plasma concentration is not expected to have any clinical consequences.

7.4 Beta Blockers Concomitant therapy with beta-adrenergic blockers and verapamil may result in additive negative effects on heart rate, atrioventricular conduction, and/or cardiac contractility. The combination of extended-release verapamil and beta-adrenergic blocking agents has not been studied. However, there have been reports of excess bradycardia and AV block, including complete heart block, when the combination has been used for the treatment of hypertension. For hypertensive patients, the risk of combined therapy may outweigh the potential benefits. The combination should be used only with caution and close monitoring. Asymptomatic bradycardia (36 beats/min) with a wandering atrial pacemaker has been observed in a patient receiving concomitant timolol (a beta-adrenergic blocker) eyedrops and oral verapamil. A decrease in metoprolol and propranolol clearance has been observed when either drug is administered concomitantly with verapamil. A variable effect has been seen when verapamil and atenolol were given together.

7.5 Digitalis Consider reducing digoxin dose when verapamil and digoxin are to be given together. Monitor digoxin level periodically during therapy. Chronic verapamil treatment can increase serum digoxin levels by 50% to 75% during the first week of therapy, and this can result in digitalis toxicity. In patients with hepatic cirrhosis the influence of verapamil on digoxin pharmacokinetics is magnified. Verapamil may reduce total body clearance and extrarenal clearance of digoxin by 27% and 29%, respectively. If digoxin toxicity is suspected, suspend or discontinue digoxin therapy. In previous clinical trials with other verapamil formulations related to the control of ventricular response in patients taking digoxin who had atrial fibrillation or atrial flutter, ventricular rates below 50/min at rest occurred in 15% of patients, and asymptomatic hypotension occurred in 5% of patients.

7.6 Alcohol Verapamil has been found to significantly inhibit ethanol elimination resulting in elevated blood ethanol concentrations that may prolong the intoxicating effects of alcohol.

7.7 Clonidine Sinus bradycardia resulting in hospitalization and pacemaker insertion has been reported in association with the use of clonidine concurrently with verapamil. Monitor heart rate in patients receiving concomitant verapamil and clonidine.

7.8 Telithromycin Hypotension and bradyarrhythmias have been observed in patients receiving concurrent telithromycin, an antibiotic in the ketolide class of antibiotics.

7.9 Antineoplastic Agents Verapamil can increase doxorubicin levels. The absorption of verapamil can be reduced by the cyclophosphamide, oncovin, procarbazine, prednisone (COPP) and the vindesine, adriamycin, cisplatin (VAC) cytotoxic drug regimens. Concomitant administration of R verapamil can decrease the clearance of paclitaxel.

7.10 Quinidine In a small number of patients with hypertrophic cardiomyopathy, concomitant use of verapamil and quinidine resulted in significant hypotension. Until further data are obtained, avoid combined therapy of verapamil and quinidine in patients with hypertrophic cardiomyopathy. The electrophysiological effects of quinidine and verapamil on AV conduction were studied in 8 patients. Verapamil significantly counteracted the effects of quinidine on AV conduction. There has been a report of increased quinidine levels during verapamil therapy.

7.11 Aspirin In a few reported cases, coadministration of verapamil with aspirin has led to increased bleeding times greater than observed with aspirin alone.

7.12 Antihypertensive Agents Verapamil administered concomitantly with oral antihypertensive agents (e.g., vasodilators, angiotensin-converting enzyme inhibitors, diuretics, beta blockers) will usually have an additive effect on lowering blood pressure. Monitor patients receiving these combinations appropriately. Concomitant use of agents that attenuate alpha-adrenergic function with verapamil may result in reduction in blood pressure that is excessive in some patients. Such an effect was observed in one study following the concomitant administration of verapamil and prazosin.

7.13 Disopyramide Until data on possible interactions between verapamil and disopyramide are obtained, do not administer disopyramide within 48 hours before or 24 hours after verapamil administration.

7.14 Flecainide A study in healthy volunteers showed that the concomitant administration of flecainide and verapamil may have additive effects on myocardial contractility, AV conduction, and repolarization. Concomitant therapy with flecainide and verapamil may result in additive negative inotropic effect and prolongation of atrioventricular conduction.

7.15 Carbamazepine Verapamil therapy may increase carbamazepine concentrations during combined therapy. This may produce carbamazepine side effects such as diplopia, headache, ataxia, or dizziness.

7.16 Cyclosporine Verapamil therapy may increase serum levels of cyclosporine.

7.17 Lithium Increased sensitivity to the effects of lithium (neurotoxicity) has been reported during concomitant verapamil-lithium therapy with either no change or an increase in serum lithium levels. However, the addition of verapamil has also resulted in the lowering of serum lithium levels in patients receiving chronic stable oral lithium. Patients receiving both drugs must be monitored carefully.

7.18 Inhalation Anesthetics Animal experiments have shown that inhalation anesthetics depress cardiovascular activity by decreasing the inward movement of calcium ions. When used concomitantly, inhalation anesthetics and calcium antagonists, such as verapamil, titrate slowly to avoid excessive cardiovascular depression.

7.19 Neuromuscular Blocking Agents Clinical data and animal studies suggest that verapamil may potentiate the activity of neuromuscular blocking agents (curare-like and depolarizing). It may be necessary to decrease the dose of verapamil and/or the dose of the neuromuscular blocking agent when the drugs are used concomitantly.

7.20 Phenobarbital Phenobarbital therapy may increase verapamil clearance.

7.21 Rifampin Therapy with rifampin may markedly reduce oral verapamil bioavailability.

7.22 Theophylline Verapamil may inhibit the clearance and increase the plasma levels of theophylline.

7.23 Cimetidine The interaction between cimetidine and chronically administered verapamil has not been studied. Variable results on clearance have been obtained in acute studies of healthy volunteers; clearance of verapamil was either reduced or unchanged.

7.24 Nitrates Verapamil has been given concomitantly with short- and long-acting nitrates without any undesirable drug interactions. The pharmacologic profile of both drugs and the clinical experience suggest beneficial interactions.

7.25 Mammalian Target of Rapamycin (mTOR) Inhibitors In a study of 25 healthy volunteers with co-administration of verapamil with sirolimus, whole blood sirolimus C max and AUC were increased 130% and 120%, respectively. Plasma S(-) verapamil C max and AUC were both increased 50%. Co-administration of verapamil with everolimus in 16 healthy volunteers increased the C max and AUC of everolimus by 130% and 250%, respectively. With concomitant use of mTOR inhibitors (e.g., sirolimus, temsirolimus, and everolimus) and verapamil, consider appropriate dose reductions of both medications.

CONTRAINDICATIONS Verapamil hydrochloride injection is contraindicated in: Severe hypotension or cardiogenic shock. Second-or third-degree AV block (except in patients with a functioning artificial ventricular pacemaker). Sick sinus syndrome (except in patients with a functioning artificial ventricular pacemaker). Severe congestive heart failure (unless secondary to a supraventricular tachycardia amenable to verapamil hydrochloride therapy). Patients receiving intravenous beta-adrenergic blocking drugs (e.g., propranolol). Intravenous verapamil hydrochloride 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. 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 hydrochloride is administered. Therefore, the use of verapamil hydrochloride in these patients is contraindicated. Ventricular tachycardia: Administration of intravenous verapamil hydrochloride to patients with wide-complex ventricular-tachycardia (QRS ≥ 0.12 sec) can result in marked hemodynamic deterioration and ventricular fibrillation. Proper pre-therapy diagnosis and differentiation from wide-complex supraventricular tachycardia is imperative in the emergency room setting. Known hypersensitivity to verapamil hydrochloride.

WARNINGS VERAPAMIL HYDROCHLORIDE INJECTION 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 United States. 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: 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 hydrochloride 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 hydrochloride 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 hydrochloride and all forms of disopyramide phosphate are obtained, disopyramide should not be administered within 48 hours before or 24 hours after verapamil hydrochloride administration. Flecainide: A study in healthy volunteers showed that the concomitant administration of flecainide and verapamil hydrochloride may have additive effects reducing myocardial contractility, prolonging AV conduction, and prolonging repolarization.

Heart

Block: Verapamil hydrochloride prolongs AV conduction time. While high-degree AV block has not been observed in controlled clinical trials in the U.S., 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 hydrochloride 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.