Changing rates and patterns of drug resistance mutations in antiretroviral-experienced HIV-infected patients.

Surveillance of drug resistance mutations in antiretroviral-experienced HIV(+) patients may provide useful information regarding options available for rescue interventions. All resistance tests performed from 1999 to 2005 on antiretroviral-experienced individuals at one reference laboratory in Madrid were examined. Only mutations associated with drug resistance recorded at the September 2006 IAS-USA list were considered. A total of 2137 specimens were analyzed. Overall, 71.1% showed resistance mutations to at least one drug class, 56.1% to at least two, and 21% to all three drug families. Resistance mutations were 65% for NRTI, 44.4% for NNRTI, and 42.5% for PI. Mutations T215Y/F, M184V, and M41L were the most frequent for NRTI. Their rate significantly declined since 1999. K65R significantly increased since 1999 (0.8%) to 2003 (7.3%) but declined up to 3.3% in 2005. For NNRTI, K103N significantly increased from 21.8% in 1999 to 29.5% in 2005 (p < 0.01). The most frequent PI resistance mutations were L90M (24.3%), V82X (19.9%), M46I/L (19.5%), and I54V (17.1%). The presence of five or more was 58.8% in 1999 but declined to 22.2% in 2005. The rate of drug resistance mutations causing NRTI and PI resistance has steadily declined in antiretroviral-experienced patients since 1999. The availability of a large number and/or more convenient NRTI as well as the wide use of ritonavir-boosted PI could explain these observations. However, broad PI cross-resistance was seen in nearly 25% of antiretroviral-experienced patients in 2005. Therefore, there is a still need for new antiretrovirals with different resistance profiles.