ObjectivesTo describe the prevalence of baseline drug-resistance mutations, resistance to antiretroviral drugs, and the subsequent virological response to therapy in treatment-naïve patients from Mexico with established HIV-1 infection. MethodsResistance testing was performed on plasma samples from antiretroviral-naïve patients. Data on mutations associated with antiretroviral drug resistance were obtained using Stanford software (http://hivdb.stanford.edu). ResultsNinety-six treatment-naïve individuals were enrolled in the study during 2002-2003. Of these, 83 patients (86%) had at least one resistance mutation and 15 (16%) had drug resistance. At baseline, the mean plasma viral load was 299 834 HIV-1 RNA copies/mL, and at follow-up it was 37 620 copies/mL (Po0.0001). Primary mutations in the reverse transcriptase region were observed in 15% of patients. For nucleoside inhibitors, mutations T215Y/C and F77L (3%) and D67N/S, T69N and M184V (2%), were detected. For nonnucleoside inhibitors, mutations K103N/R (6%), Y181C (3%) and G190A (2%) were detected. Overall, 6% of patients showed resistance to delavirdine and nevirapine, 4% to efavirenz, and 2% to lamivudine and nelfinavir. Twelve patients showed no response to treatment and three of these patients had antiretroviral drug resistance. ConclusionsThe prevalence of baseline drug-resistance mutations found in this study was similar to that found in previous reports for newly HIV-infected individuals, although access to and management of antiretrovirals in Mexico are different.