Development and significance of resistance to protease inhibitors in HIV-1-infected adults under triple-drug therapy in clinical practice.

Development of drug resistance is considered a major cause for failure of antiretroviral therapy in human immunodeficiency virus type 1 (HIV-1)-infected patients adherent to treatment. However, the rate of emergence and the significance of HIV-1 drug resistance in clinical practice have been not investigated thoroughly. Selection of HIV-1 variants that are genotypically resistant to protease inhibitors was studied in all the patients (n = 169) who completed at least 18 months of treatment with a protease inhibitor plus two nucleoside reverse transcriptase inhibitors at two urban Italian hospitals. HIV-1 carrying primary protease inhibitor resistance mutations was detected in 70 (41.4%) patients. The estimated proportion of patients developing genotypic resistance to protease inhibitors at 12 and 24 months was 18.3% (95% CI, 12.5-24.2%) and 33.9% (95% CI, 26.4-41.5%), respectively. Independent predictors of development of resistance to protease inhibitors were higher HIV-1 RNA levels at the nadir (P < 0.0001) and inclusion of ritonavir or saquinavir versus indinavir in the starting regimen (P = 0.0313). Resistance to protease inhibitors was strongly associated with a lower response to treatment, as shown by HIV-1 RNA load (P = 0.0001) and CD4 cell counts (P = 0.005). However, a linear increase in CD4 cell counts was maintained up to the end of follow-up even in the protease inhibitor-resistant population. Resistance to protease inhibitors develops in a relevant proportion of patients under long-term triple-drug therapy in clinical practice and is associated with virological treatment failure and limitation of CD4 cell increase.

Divergent distribution of HIV-1 drug-resistant variants on and off antiretroviral therapy.

OBJECTIVE: To investigate the distribution of drug-resistant HIV-1 variants in plasma RNA and peripheral blood monuclear cell (PBMC) DNA at treatment failure while on therapy and after stopping therapy. DESIGN: Fifty-eight patients failing their first highly active antiretroviral treatment while on therapy and 50 patients after a median of 18.6 weeks after treatment interruption following multiple treatment failures were analysed. METHODS: Paired plasma HIV-1 RNA and PBMC HIV-1 DNA were used for genotypic antiretroviral resistance testing. Drug resistance was computed by using the Stanford on-line genotype interpretation system. RESULTS: The extent of drug resistance was larger in plasma RNA than in PBMC DNA in the on-therapy group (P=0.004) and in PBMC DNA than in plasma RNA in the off-therapy group (P=0.04). Interpretation of genotype based on PBMC DNA and plasma RNA in the on-therapy and in the off-therapy group would have missed detection of resistance to one or more drugs in 21 and 22% of the patients, respectively, compared to interpretation based on the other blood compartment. In a subset of 27 patients for whom a sample before stopping therapy was available, there was a significant decrease in the number of RNA (mean 8.1 to 5.3, P=0.004), but not DNA (mean 6.8 to 5.7, P=0.143), resistance mutations following treatment interruption. CONCLUSION: While plasma RNA is the material of choice for early detection of drug resistance while on therapy, analysis of PBMC DNA may additionally support and possibly improve sensitivity of resistance testing in the absence of therapy.