Resistance and Virological Response Analyses in a Three Initial Treatment Strategy Trial: A Substudy of the INITIO Trial

Purpose: To study the impact of baseline resistance mutations and HIV-1 subtypes on virological response to first-line antiretroviral therapy and to analyse the concordance of the results of two antiretroviral resistance interpretation tools in the INITIO trial. Method: Genotype and virco (R) TYPE resistance analyses were studied at baseline, Year 2, Year 3, and at first therapeutic failure on plasma specimens stored at -80 degrees C. Relations between resistance mutations at baseline, subtype, initial virological response, and virological outcome after Week 24 were studied. Results: 781 participants had genotypic results available at baseline. Therapeutic failure occurred for 112 participants. Initial virological response as well as virological outcome after Week 24 were not associated with HIV subtype. Before Week 24, the proportion of participants remaining under strict initial regimen was lower in patients with resistance mutations at baseline than in those without any resistance mutations. Presence of resistance mutations at baseline also impacted negatively long-term virological outcome. Few discrepancies were observed between genotypic and virco (R) TYPE for resistance interpretation. Conclusion: These data showed that presence of resistance mutations at baseline was associated with a poorer long-term virological outcome in the INITIO trial.