Drug Interaction Report

MONITOR: Beta-blockers may antagonize the cardiostimulatory effects of ephedrine by blocking beta-1 adrenergic receptors in the heart. Parenteral ephedrine may be less effective in the treatment of shock and hypotension if the patient is receiving, or has recently received, a beta-blocking drug. In addition, peripheral vascular resistance may increase due to unopposed alpha-adrenergic effect of ephedrine in the presence of beta-blockade. Theoretically, the interaction may also occur with beta-blocker ophthalmic preparations, since they may be systemically absorbed and can produce clinically significant systemic effects even at low or undetectable plasma levels.

MANAGEMENT: Clinicians should be alert to the potential for diminished cardiac response when parenteral ephedrine is used in patients treated with beta-blockers, including ophthalmic formulations.

GENERALLY AVOID: Noncardioselective beta-blockers can antagonize the bronchodilating effects of ephedrine by blocking beta-2 adrenergic receptors in smooth muscles of the bronchial tree. The interaction is less likely to occur with cardioselective beta-blockers, which generally have little effect on beta-2 adrenergic receptors at therapeutic dosages. However, cardioselectivity is not absolute and may be lost with larger doses.

MANAGEMENT: Noncardioselective beta-blockers, including ophthalmic formulations, should generally be avoided in patients using ephedrine-containing preparations for bronchospastic diseases. If beta-blocker therapy is necessary, an agent with beta-1 selectivity (e.g., atenolol, metoprolol, betaxolol) is considered safer. However, caution is advised, especially with higher dosages of the beta-blocker.

GENERALLY AVOID: Moderate-to-high dietary intake of potassium, especially salt substitutes, may increase the risk of hyperkalemia in some patients who are using angiotensin II receptor blockers (ARBs). ARBs can promote hyperkalemia through inhibition of angiotensin II-induced aldosterone secretion. Patients with diabetes, heart failure, dehydration, or renal insufficiency have a greater risk of developing hyperkalemia.

MANAGEMENT: Patients should receive dietary counseling and be advised to not use potassium-containing salt substitutes or over-the-counter potassium supplements without consulting their physician. If salt substitutes are used concurrently, regular monitoring of serum potassium levels is recommended. Patients should also be advised to seek medical attention if they experience symptoms of hyperkalemia such as weakness, irregular heartbeat, confusion, tingling of the extremities, or feelings of heaviness in the legs.

MONITOR: Coadministration of two or more sympathomimetic agents may increase the risk of adverse effects such as nervousness, irritability, and increased heart rate. Central nervous system (CNS) stimulants, particularly amphetamines, can potentiate the adrenergic response to vasopressors and other sympathomimetic agents. Additive increases in blood pressure and heart rate may occur due to enhanced peripheral sympathetic activity.

MANAGEMENT: Caution is advised if two or more sympathomimetic agents are coadministered. Pulse and blood pressure should be closely monitored.