Population trends in the prevalence and patterns of protease resistance related to exposure to unboosted and boosted protease inhibitors

BACKGROUND: In recent years, several new drugs from the protease inhibitor (PI) class designed to treat HIV infection have become available and the use of ritonavir-boosting has increased in popularity. These changes might be expected to affect the prevalence and patterns of protease resistance in the population of patients who experience treatment failure. METHODS: The UK HIV Drug Resistance Database aims to capture the results of all genotypic resistance tests conducted nationally. Tests on antiretroviral therapy-experienced patients were identified through linkage with the UK Collaborative HIV Cohort Study, from which detailed clinical information on these patients, including a full antiretroviral therapy history, was obtained. RESULTS: Analyses were on the basis of 8,553 genotypic resistance tests carried out between 1998 and 2005, during which time the overall prevalence of protease resistance halved from 35% to 16%. Substantial declines were observed regardless of whether the patient had been exposed to unboosted PIs and/or boosted PIs. The frequency of protease resistance among patients who had received boosted PIs fell sharply until 2002 with a weaker trend thereafter, falling to 12% in 2005. Individual mutations L33F, M461/L, V82A/F/T/S/L and 184V became relatively more frequent over the period of study. CONCLUSIONS: The decline in protease resistance was partly due to increasing use of ritonavir-boosting. Nonetheless, the prevalence of resistance was higher than suggested by clinical trials, indicating that prolonged exposure to a boosted PI could ultimately select for major protease mutations.