Coadministration has not been studied. Based on metabolism and clearance a clinically significant interaction is unlikely with emtricitabine as cidofovir is eliminated renally via glomerular filtration and active renal secretion by OAT1 and OAT3. Since tenofovir is primarily eliminated by the kidneys, coadministration with drugs that reduce renal function or compete for active tubular secretion may increase concentrations of tenofovir or the coadministered drug. Tenofovir-DF should be avoided with concurrent or recent use of a nephrotoxic agent. If concomitant use of tenofovir-DF and nephrotoxic agents is unavoidable, renal function should be monitored closely.