toprol-xl and Norpace cr Interactions

Interactions between toprol-xl(metoprolol) and Norpace cr (disopyramide)

metoprolol and disopyramide (Major Drug-Drug)

GENERALLY AVOID: Due to its potent negative inotropic and chronotropic effects, disopyramide has been associated with severe hypotension, syncope, severe bradycardia, asystole, and heart failure when used with beta-blockers. Fatalities have been reported. In addition, QT interval prolongation and excessive QRS complex widening may occur with concurrent administration of disopyramide and beta-blockers in the treatment of arrhythmias. Some beta-blockers have also been reported to decrease the clearance of disopyramide. No significant drug interaction was reported when disopyramide was coadministered with oral propranolol in healthy subjects.

MONITOR CLOSELY: The use of disopyramide has been associated with rare cases of significant hypoglycemia. Since beta-blockers may inhibit some of the normal physiologic response to hypoglycemia, glucoregulatory mechanisms (in the absence of food) may be compromised. Specifically, inhibition of catecholamine-mediated glycogenolysis and glucose mobilization in association with beta-blockade can potentiate the hypoglycemia and delay recovery of normal blood glucose levels. In addition, symptoms of hypoglycemia such as tremors and tachycardia may be absent, making it more difficult for patients to recognize an oncoming episode. These effects may be more likely with noncardioselective beta-blockers (e.g., propranolol, pindolol, timolol) but may occasionally also occur with relatively beta-1 selective agents (e.g., atenolol, metoprolol), particularly at higher dosages.

MANAGEMENT: The use of disopyramide in combination with beta-blockers should generally be avoided unless the benefits are anticipated to outweigh the risks. Close monitoring of cardiac output, blood pressure, heart rate, and/or ECG is recommended if these drugs must be used together. Patients should be advised to seek medical attention if they experience dizziness, lightheadedness, syncope, palpitations, slow or fast pulse, or irregular heartbeats.