Drug Interaction Report

MONITOR: Coadministration with inhibitors and/or substrates of organic cation transporter 2 (OCT2) may increase the plasma concentrations of dalfampridine. In vitro studies have shown that OCT2 is the primary transporter responsible for the active tubular secretion of dalfampridine, which accounts for approximately 60% of its renal elimination - the major route of clearance for dalfampridine. When a single 10 mg dose of dalfampridine was administered to 23 healthy volunteers with the OCT2 inhibitor cimetidine (400 mg every 6 hours), dalfampridine systemic exposure (AUC) was 25% higher relative to the reference value. The interaction has not been studied with OCT2 substrates, but competitive inhibition for active tubular secretion is possible. Elevated plasma levels of dalfampridine may increase the risk of adverse effects, particularly seizures.

MANAGEMENT: Caution is advised when dalfampridine is used with OCT2 inhibitors and/or substrates. The potential benefits of concomitant use should be considered against the risk of seizures.

Food enhances the oral absorption and bioavailability of tenofovir, the active entity of tenofovir disoproxil fumarate. According to the product labeling, administration of the drug following a high-fat meal increased the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of tenofovir by approximately 14% and 40%, respectively, compared to administration in the fasting state. However, administration with a light meal did not significantly affect the pharmacokinetics of tenofovir compared to administration in the fasting state. Food delays the time to reach tenofovir Cmax by approximately 1 hour. Tenofovir disoproxil fumarate may be administered without regard to meals.