Children who had a history of mono or dual NRTI therapy before starting NNRTI-based ART, or who received an NRTI backbone other than zidovudine plus lamivudine or stavudine plus lamivudine, were excluded from the study. Retrospective data collection was performed using a standardized data collection form. Information obtained from medical records included patient demographics, HIV Centers for Disease Control and
Prevention (CDC) clinical classification, history of ART, CD4 cell count and percentage and plasma HIV RNA measurements during DAPT nmr receipt of NNRTI-based highly active antiretroviral therapy (HAART) and prior to switching to PI-based HAART, and genotypic resistance test results before switching to PI. During the period under study, viral load was not monitored routinely, but generally tested at the time of clinical or immunological failure. The study was approved by the Institutional Review Boards of all sites. The interpretation of mutations was based on the guidelines published by the International AIDS Society (IAS)-USA Drug Resistance Mutations group .
For this study, NRTI resistance mutations included M41L, D67N, K70R, L210W, T215F/Y, and K219Q/E thymidine analogue-associated mutations (TAMs), the Q151M complex, the 69 insertion complex, K65R, L74V, K70E, Y115F and M184V/I. Multi-NRTI resistance was defined as having Dapagliflozin at least four TAMs or the presence of Q151M or the 69 insertion. NNRTI-associated mutations included V90I, A98G, L100I, K101E/H/P, K103N, V106A/M, HCS assay V108I, E138A, V179D/F/T, Y181C/I/V, Y188C/L/H, G190S/A, P225H and M230L. The etravirine-weighted mutation score was calculated according to the importance of the mutations . Four mutations merited a weighting factor of 4: L100I, K101P and Y181C/I. Mutations with a weighting factor of 3 were E138A/G, V179E, G190Q, M230L and K238N. Weighting scores of 2 were assigned to K101E,
V106A, E138K, V179L and Y188L, while mutations at 11 sites had a score of 1: V90I, K101H, V106M, E138Q, V179D/F/M, Y181F, V189I, G190E/T, H221Y, P225H and K238T. A weight mutation score of ≥4 was interpreted as being associated with a significant reduction in etravirine efficacy . Genotypic resistance testing was performed using the TruGene HIV-1 Genotyping system (Visible Genetics, Inc., Toronto, Canada) at five sites, the ViroSeq HIV-1 Genotyping System (Celera Diagnostics, Alameda, CA) at one site, and an in-house method using Stanford and IAS databases  at two sites. Descriptive analyses were performed to describe baseline patient characteristics, using median (interquartile range) and frequencies as appropriate. The proportions of patients with various NRTI- and NNRTI-associated mutations were determined.