Drug Interaction Report

MONITOR: Theoretically, topical administration of minoxidil may potentiate the hypotensive effects of systemic minoxidil and other vasodilators. Although systemic absorption of topical minoxidil is generally minimal (approximately 1.6% to 3.9% of an applied dose), adverse cardiovascular effects such as edema, palpitations, blood pressure decreases, and increased pulse rate have been reported in a few patients. Increased systemic absorption may occur when topical minoxidil is used in excess of normally recommended dosages or applied to compromised skin.

MANAGEMENT: Patients prescribed topical minoxidil in combination with systemic vasodilators or peripherally-acting antiadrenergic agents should be monitored for orthostatic signs and symptoms, including increase in heart rate, decrease in standing blood pressure, dizziness, and headache.

GENERALLY AVOID: The concurrent use of ethanol and alpha-1 adrenergic blockers may cause increased hypotensive effects. Patients with aldehyde dehydrogenase deficiencies (primarily Asians) may be at a higher risk of this interaction. The mechanism has not been determined. Data exist for prazosin and other alpha adrenergic blockers are expected to interact also. In addition, any patients taking alpha adrenergic blockers may experience excessive orthostatic hypotension with ethanol ingestion, due to ethanol's unopposed vasodilatory effects in the presence of alpha adrenergic blockade.

MANAGEMENT: Patients who develop a flushing reaction after ethanol ingestion (indicates a possible aldehyde dehydrogenase deficiency) should be advised to avoid ethanol or limit their intake. All patients should be warned about the possibility of orthostatic hypotension with concurrent ethanol use.