All of the patients also took tenofovir disoproxil and emtricitabine (other antiviral medicines); The other three studies involved adults who were already receiving HIV treatment but were not responding to it: • one study compared ritonavir-boosted Prezista with ritonavir-boosted lopinavir in 604 patients who had taken some anti-HIV medicines in the past; • two studies involved 628 patients who had taken many anti-HIV medicines in the past and compared ritonavir-boosted Prezista with other protease inhibitors chosen on the basis of the patient’ s previous treatments and predicted response.