It is important to monitor trends over time in these indicators to assess whether levels of success are maintained,

or even improved. For the overwhelming majority of people treated to date, ART has been based on the use of drugs from three original classes; nonnucleoside reverse transcriptase inhibitors (NNRTIs); nucleo(t)side reverse transcriptase Vincristine inhibitors [N(t)RTIs]; and protease inhibitors (PIs). Increasing numbers of patients have experienced multiple virological failure, with those who initiated therapy with mono or dual nucleoside therapy before the highly active antiretroviral therapy (HAART) era at particularly high risk [8,9]. Drugs are now available from three other classes (integrase inhibitors, CCR5 antagonists and a fusion inhibitor) and, in addition, there are also some newer generation drugs from the existing classes (e.g. the PI darunavir and the NNRTI etravirine) Enzalutamide supplier [10–13]. Data on the levels of viral suppression to <50 copies/mL in trials of these drugs suggest that patients in routine

practice who have experienced extensive failure of drugs in the original three classes increasingly have the possibility of experiencing viral suppression to <50 copies/mL [11,12,14]. Even so, there is a group of patients for whom viral load remains unsuppressed on ART and in whom the possibility of exhausting all treatment options is likely to remain for the foreseeable future. Monitoring of trends in the number of patients who have experienced multiple drug failure, and the number

of such patients who have a current viral load >50 copies/mL, is important for understanding the likely durability of ART success. In this paper, we present trends over calendar time in key indicators of treatment success and failure from the UK Collaborative HIV Cohort (CHIC) Study, a large multi-clinic cohort of people seen for HIV care. Our estimates at a UK level also incorporate data from the Health Protection Agency (HPA) Survey of Prevalent HIV Infections Diagnosed (SOPHID) STK38 study and update trends from UK CHIC published in 2005 [5]. A previously validated model of HIV progression and the effect of ART, which simulates reconstructed individual patient histories for the infected population in the United Kingdom [15], is used to project future trends in these indicators. Data from the UK CHIC Study and SOPHID studies were used for these analyses. The UK CHIC Study is an observational cohort study of HIV-infected individuals attending some of the largest HIV clinical centres in the United Kingdom; the data set used for the current analysis includes information from 11 centres (see Appendix) [16]. Data collected include information on patient demographics, antiretroviral history, laboratory findings, AIDS-defining events and death. ART data are in the form of start and stop dates for each period of use of each drug, so the drug regimen on any one given day can be reconstructed.