Drug Interaction Report

MONITOR: Postganglionic adrenergic blocking agents may potentiate the pharmacologic effects of direct-acting sympathomimetic amines, while the hypotensive effect of the former may be diminished. Postganglionic adrenergic blocking agents such as guanadrel, guanethidine, and rauwolfia alkaloids work by depleting catecholamine stores from adrenergic nerve endings, thus they may sensitize adrenergic receptors to direct-acting sympathomimetics. Clinically, hypertension and other cardiovascular adverse effects may occur.

MANAGEMENT: Due to their pressor effect, sympathomimetic amines should be used cautiously in patients with hypertension. Conversely, alternatives to postganglionic adrenergic blocking agents should be considered in patients treated with sympathomimetic amines. If the combination is used, blood pressure and heart rate should be closely monitored.

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients should also avoid driving or operating hazardous machinery until they know how the medications affect them.