Results from a Phase 3 head-to-head study showed that a significantly greater percent (77 percent) of treatment-experienced HIV-1 infected adults* taking Prezista? (darunavir)/ritonavir, with an optimised background regimen (OBR) of antiretroviral agents, reached a viral load of less than 400 copies/mL at week 48, compared to 68 percent of patients taking the widely prescribed medication lopinavir/ritonavir, with OBR, in a per-protocol analysis (95 percent confidence interval 2-16). In addition, significantly more patients receiving darunavir/r in this study reached an undetectable viral load (<50 copies/mL) compared to patients taking lopinavir/r (71 percent vs. 60 percent).