Risk factors for raltegravir resistance development in clinical practice

To investigate the best conditions of raltegravir use to avoid the selection of resistance mutations in the three main genetic pathways: 148, 155 and 143.A total of 161 patients failing on raltegravir with two consecutive HIV-1 viral loads20 copies/mL were studied. Ten parameters [HIV-1 RNA and CD4 at baseline and failure, genotypic sensitivity score (GSS) of treatment associated with raltegravir, protease inhibitors used, time spent on raltegravir, subtype, sex and age] were tested in univariate and multivariate logistic regression analyses and compared with the emergence of resistance mutations to raltegravir at failure. Phenotypic susceptibility to raltegravir was studied in 16 patients without the main resistance mutations to raltegravir at failure.At raltegravir failure, 46/161 patients (28.6%) had integrase resistance mutations, whereas 115/161 (71.4%) had no resistance mutations. High HIV-1 viral load level at failure (OR = 2.81, 95% CI 1.8-4.6, P 0.001) and low GSS of treatment associated with raltegravir (OR = 11.6, 95% CI 4.5-36.4, P 0.001) were independently associated with the selection of raltegravir mutations. The percentages of patients with integrase resistance mutations were 7.7% (6/78) versus 48.1% (40/83) when viral load is ≤200 or200 copies/mL and 47.5% (39/82) versus 8.9% (7/79) when GSS is2 or ≥2. Among patients without main resistance mutations, two patients showed raltegravir phenotypic resistance, one naturally with F121Y at baseline and the other acquiring G118R at failure.Our results show that to avoid the selection of raltegravir resistance mutations, patients have to be treated with at least two active drugs in combination with raltegravir and to maintain a viral load ≤200 copies/mL.