Coadministration has not been studied. Based on metabolism and clearance a pharmacokinetic interaction is unlikely as celecoxib is metabolised mainly by CYP2C9. However, coadministration could potentially result in increased risk of nephrotoxicity. Cases of acute renal failure after initiation of high dose or multiple NSAIDs have been reported in patients treated with tenofovir-DF and with risk factors for renal dysfunction. The risk is 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.