Evaluation of potential losartan-phenytoin drug interactions in healthy volunteers.

Background: Phenytoin, a cytochrome P450 (CYP) 2C9 substrate, has a narrow therapeutic index and nonlinear pharmacokinetics. Therefore there is the potential for significant concentration-related adverse effects when phenytoin is coadministered with other CYP2C9 substrates. Losartan, an antihypertensive agent, is also a substrate for CYP2C9.