Coadministration has not been studied. A clinically significant interaction with emtricitabine is unlikely. In vitro data suggest that naproxen is a weak inhibitor of OCT2, and also inhibits the renal transporters OAT1 and OAT3 (which are involved in tenofovir excretion). Renal elimination of tenofovir-DF could potentially decrease, thereby increasing the risk of nephrotoxicity. The risk is also increased if an NSAID is used for a long duration, if the patient has a pre-existing renal dysfunction, has a low body weight, or receives other drugs that may increase tenofovir exposure. Alternatives to NSAIDs should be considered in patients at risk for renal dysfunction. If emtricitabine/tenofovir-DF is co-administered with an NSAID, renal function should be monitored adequately.