When licensed, new drugs are widely used in patients failing antiretroviral therapy, including patients with multiple failures. In such patients, having multi-resistant virus, the introduction of one new drug only in the salvage regimen will infrequently result in undetectable virus load in the plasma. Tenofovir DF and atazanavir appear promising because of their pharmacokinetic profile, activity, safety and resistance properties. In addition, pharmacokinetic data in healthy volunteers suggest that atazanavir could be optimized by adding ritonavir at low dose. Thus, one may speculate that atazanavir pharmacokinetic and antiviral activity could be optimized by adding ritonavir at low dose in patients exhibiting high rate of protease inhibitor mutations.