1. Availability of antiretroviral drugs active against resistant HIV isolates. Clinicians would be more prone to switch to a new salvage regimen if the new regimen contains a new class of drugs and/or at least three drugs without cross resistance with the antiretroviral included in the failing regimen. This scenario is very likely after first or second regimen failure. However, after third regimen failure the possibilities of including at least three active drugs dramatically decrease. For deep salvage the possibilities of constructing a viable rescue regimen often depends on enrolling the patient in a clinical trial of a new antiretroviral (for example CCR5 inhibitors). Enrolment in the trial very often implies that patients have to wait for an undefined period of time until the trial starts.