In a study performed in healthy volunteers co-administration of atazanavir 300 mg with TPV/ r 500/ 100 mg bid resulted on one hand in a marked increase of Tipranavir exposure (notably Cp12h ratio of 1.75 with 90% CI [1.39-2.20]) and ritonavir exposure (AUC ratio of 1.51 with 90% CI [1.24- 1.83] and Cmax ratio of 1.38 with 90% CI [1.13-1.67]) associated with a risk of over-toxicity and on the other hand on a marked decrease of atazanavir exposure associated with a risk of loss of efficacy (AUC0-24h ratio of 0.32 with 90% CI [0.29-0.36], Cmax ratio of 0.43 with 90% CI [0.38-0.50] and Cp24h ratio of 0.19 with 90% CI [0.15-0.24]).