Resistance development over 144 weeks in treatment-naive patients receiving tenofovir disoproxil fumarate or stavudine with lamivudine and efavirenz in Study 903

Objective Study 903 was a 144-week, randomized, double-blind, active-controlled study of tenofovir disoproxil fumarate (TDF) therapy in treatment-naive HIV-1-infected patients. Patients received either TDF (n=299) or stavudine (d4T) (n=301) with lamivudine (3TC) and efavirenz (EFV). Resistance analyses were performed at baseline and at virological failure to determine the effects of baseline resistance and the patterns of resistance at virological failure. Methods Plasma HIV-1 from patients at baseline and at virological failure (> 400 HIV-1 RNA copies/mL at week 144 or early discontinuation) was analysed phenotypically and by population sequencing. Results Sixteen per cent of patients were classified as having virological failure (47 on TDF and 49 on d4T; P=0.91). Patients with non-B HIV-1 subtypes or baseline nucleoside reverse transcriptase inhibitor (NRTI)-associated mutations responded similarly to the overall population. Resistance to EFV (K103N and others) or 3TC (M184V) developed most frequently (8.3% and 5.8%, respectively) and similarly in the two arms. In the d4T arm, a variety of NRTI mutations developed: K65R (n=2), L74V (n=2), V75M (n=1), and T69A+Y115H (n=1). K65R developed in eight TDF patients (2.7%); in seven of these eight patients, within 48 weeks. All eight patients began new regimens with a protease inhibitor (PI) and NRTIs, including two patients who remained on TDF; five of the eight patients achieved HIV RNA < 50 copies/mL in second-line therapy with the remaining patients having no follow-up or being nonadherent. Conclusions Treatment of HIV-1 with TDF, 3TC and EFV was highly effective, with < 3% of patients developing resistance to TDF over 144 weeks.