Drug interactions between Reyataz and Truvada

ADJUST DOSE: Coadministration with tenofovir disoproxil fumarate (DF) may decrease the plasma concentrations of atazanavir. The mechanism of interaction has not been described. In healthy subjects, tenofovir DF (300 mg once a day) decreased the area under the plasma concentration-time curve (AUC) and trough plasma concentration (Cmin) of atazanavir (400 mg once a day) by 25% and 40%, respectively, compared to administration of atazanavir alone. Tenofovir AUC was increased approximately 24%. When ritonavir 100 mg was added as a booster and given simultaneously with atazanavir 300 mg once a day to highly treatment-experienced HIV subjects, coadministration of tenofovir DF (300 mg once daily for 4 weeks) resulted in atazanavir AUC and Cmin that were approximately 1.2- and 4-fold higher, respectively, than the values observed for unboosted atazanavir given at 400 mg once daily to healthy volunteers in the first study. Based on interim data, the safety profile of boosted atazanavir in treatment-experienced patients appears comparable to that of unboosted atazanavir in other clinical trials. The increase in tenofovir AUC also does not appear to be associated with increased toxicity over 24 weeks.

MANAGEMENT: In patients requiring combination therapy with atazanavir and tenofovir DF, consideration should be given to prescription of atazanavir 300 mg with ritonavir 100 mg and tenofovir DF 300 mg, all as a single daily dose with food. Caution is advised if the combination of atazanavir and tenofovir DF is administered without ritonavir as a booster, since reduced atazanavir plasma levels may lead to diminished virologic response and possible resistance to atazanavir.