An additive/subtractive genotypic score as a determinant of the virological response to didanosine in HIV-1 infected patients.

To assess the genotypic determinants of the virological response (VR) to didanosine (ddI) in nucleoside reverse transcriptase inhibitors (NRTI)-experienced patients.Human immunodeficiency virus type 1 (HIV-1) genotype was determined at baseline in 74 ddI-naive-patients with baseline viral load >500 copies/ml and receiving ddI as part of a new regimen. VR was defined as a plasma HIV-1 RNA <50 copies/ml after three months on ddI. NRTI resistance mutations associated with higher or lower frequencies of VR with a p-value<0.25 were retained in different sets of mutations, where the mutations associated with a worse VR were added, whereas the mutations associated with a better VR were subtracted. The most significant mutation scores were then studied in a multivariate analysis.Changes at three codons (M41L, L210W, T215Y/F/D/C/E) were associated with a worse VR and three mutations (K70R, M184V, K219Q) with a better VR. The strongest association with the VR was obtained with the score M41L+L210W+T215Y/F/D/C/E-K70R-K219Q. The score was independently associated with the VR in the multivariate analysis.Taking into account the mutations associated with a better VR may improve genotypic resistance algorithms. Our results are of interest for the management of antiretroviral therapy in NRTI-experienced patients.