Steady-state pharmacokinetics of emtricitabine and tenofovir disoproxil fumarate administered alone and in combination in healthy volunteers.

The approved antiretroviral drugs, emtricitabine and tenofovir disoproxil fumarate, were considered good candidates for a fixed-dose combination product that could be administered as a single pill once daily (qd), thereby simplifying existing treatment regimens and promoting patient adherence. As both drugs are extensively renally eliminated, a randomized, 3-way crossover study was conducted in 19 healthy volunteers to formally evaluate the potential pharmacokinetic interaction when the drugs are administered alone and together (ie, 200 mg emtricitabine qd for 7 days, 300 mg tenofovir disoproxil fumarate qd for 7 days, and 200 mg emtricitabine plus 300 mg tenofovir disoproxil fumarate qd for 7 days) with no washout between treatments. Steady-state pharmacokinetic parameters (AUC(tau), C(max), and C(min)) of emtricitabine and tenofovir (as tenofovir disoproxil fumarate) in combination were essentially equivalent versus each drug alone, providing a pharmacokinetic rationale for combining these products in emtricitabine/tenofovir disoproxil fumarate fixed-dose tablets.