Drug Interaction Report

GENERALLY AVOID: Theoretically, monoamine oxidase inhibitors (MAOIs) may antagonize the hypotensive effect of peripherally-acting antiadrenergic agents like guanadrel and guanethidine that work by depleting catecholamine stores from adrenergic nerve endings. MAOIs inhibit the breakdown of catecholamines and enhance storage in adrenergic neurons.

MANAGEMENT: While clinical data are lacking, guanadrel and guanethidine should preferably not be used with MAOIs or other agents that possess MAOI activity (e.g., furazolidone, linezolid, methylene blue, procarbazine). The manufacturer of phenelzine considers the combination contraindicated. At least 7 to 14 days should elapse between discontinuation of MAOI therapy and initiation of treatment with guanadrel or guanethidine. If they have been used together, clinicians should be aware that significant hypotension may occur following withdrawal of MAOI therapy.

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.