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.

ADJUST DOSING INTERVAL: Food may delay the gastrointestinal absorption of tamsulosin. The time to maximum plasma concentration (Tmax) is reached by 4 to 5 hours under fasted conditions and by 6 to 7 hours when tamsulosin is administered with food. The delay in Tmax has the desirable effect of smoothing the tamsulosin plasma concentration profile, thereby reducing fluctuation of the plasma peak and trough concentrations with multiple dosing. Food may also affect the extent of absorption of tamsulosin. It has been reported that taking tamsulosin under fasted conditions results in a 30% increase in bioavailability (AUC) and 40% to 70% increase in peak plasma concentration (Cmax) compared to fed conditions. The effects of food on the pharmacokinetics of tamsulosin are consistent regardless of whether tamsulosin is taken with a light meal or a high-fat meal.

MANAGEMENT: To ensure uniformity of absorption, tamsulosin should be administered approximately one-half hour following the same meal each day.