Drug Interaction Report

Coadministration with rizatriptan may alter the plasma concentrations of drugs that are primarily metabolized by CYP450 2D6. Rizatriptan has been shown to be a competitive inhibitor of CYP450 2D6 in vitro, but only at high, clinically irrelevant concentrations and a clinically significant inhibitory effect on CYP450 2D6 has not been demonstrated in clinical drug interaction studies. Based on these observations, rizatriptan may be administered with CYP450 2D6 substrates without the need for increased clinical monitoring

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.