Drug Interaction Report

MONITOR: The concomitant use of tocainide and beta-blockers may have additive effects on cardiac index, left ventricular function, and pulmonary wedge pressure. While significant interactions have not been reported in studies, cases of asystole have been reported in patients with preexisting electrophysiologic abnormalities after tocainide and metoprolol were coadministered. The mechanism is not known, but may be related to an additive effect on the sinus node or conduction system, especially in patients with sick sinus syndrome. Cases of confusion and paranoia have also been reported after coadministration of tocainide and propranolol.

MANAGEMENT: The concomitant use of tocainide and beta blockers should probably be avoided in patients with atrioventricular conduction abnormalities or sick sinus syndrome. This combination should be used cautiously in other patients, with careful dose titration and close clinical and electrocardiographic monitoring for efficacy and safety.

MONITOR: Topically administered alpha-2 adrenergic receptor agonists such as apraclonidine and brimonidine are systemically absorbed, with the potential for producing rare but clinically significant systemic effects such as hypotension and bradycardia. The possibility for an additive or potentiating effect on blood pressure and heart rate should be considered when used with other medications that affect these parameters, such as ophthalmic and systemic beta blockers, vasodilators, cardiac glycosides, and antihypertensive agents.

MANAGEMENT: Blood pressure and pulse rate should be monitored regularly when topical alpha-2 adrenergic receptor agonists are prescribed in combination with cardiovascular drugs. Patients should be advised to notify their physician if they experience slow pulse, irregular heartbeat, dizziness, lightheadedness, or syncope.