Coadministration with atazanavir alone decreases atazanavir concentrations. Coadministration with atazanavir/ritonavir increases tenofovir concentrations. Coadministration of atazanavir (400 mg once daily) and tenofovir-DF (300 mg once daily) was studied in 33 subjects. Tenofovir Cmax, AUC and Cmin increased by 14%, 24% and 22%, respectively. Atazanavir Cmax, AUC and Cmin decreased by 21%, 25% and 40%, respectively. Coadministration of atazanavir/ritonavir (300/100 mg once daily) and tenofovir-DF (300 mg once daily) was studied in 10 subjects. Tenofovir Cmax, AUC and Cmin increased by 34%, 37% and 29%, respectively. Atazanavir Cmax, AUC and Cmin decreased by 28%, 25% and 23%, respectively. When coadministered with Truvada, atazanavir 300 mg should be given with ritonavir 100 mg. Monitor patients receiving Truvada concomitantly with ritonavir-boosted atazanavir for TDF-associated adverse reactions. Discontinue Truvada in patients who develop TDF-associated adverse reactions.