Twice-Daily Trizivir versus Combivir-Abacavir in Antiretroviral-Experienced Adults with Human Immunodeficiency Virus-1 Infection: A Formulation-Switch Trial

Study Objective. To establish the clinical equivalence (noninferiority) of one tablet containing abacavir 300 mg-lamivudine 150 mg-zidovudine 300 mg (Trizivir) versus a tablet containing lamivudine 150 mg-zidovudine 300 mg (Combivir) given with one abacavir (ABC) 300-mg tablet, administered twice/day, in antiretroviral-experienced, human immunodeficiency virus (HIV)-1-infected patients. Design. Randomized, open-label, parallel-group, multicenter, formulation-switch study. Setting. Twenty seven outpatient treatment sites. Patients. Adults with HIV-1 RNA levels of 400 copies/ml or less and CD4 ⁺ cell counts above 200 cells/mm³ who had been treated for 16 weeks or more with highly active antiretroviral therapy containing Combivir-ABC. Intervention. Patients were randomized 1:1 to Trizivir (97 patients) or Combivir-ABC (98) for 24 weeks. Measurements and Main Results. The primary study end point was the proportion of patients who maintained less than a 0.5-log₁₀ increase from baseline in HIV-1 RNA (virologic success) through week 24. Clinical equivalence of the treatments was established if the 95.1% lower confidence limit (LCL) for the difference in proportion of virologic success with Trizivir minus Combivir-ABC was -0.12 or greater. Trizivir was clinically equivalent to Combivir-ABC. The intent-to-treat observed analysis at week 24 with Trizivir and Combivir-ABC showed a similar rate of virologic success (83% [80/97] and 77% [75/98], respectively, 95.1% LCL -0.026), of patients with HIV-1 RNA levels of 400 or fewer copies/ml (99% [82/83] and 93% [77/83], respectively, 95.1% LCL 0.021), and of patients with HIV-1 RNA levels of fewer than 50 copies/ml (89% [74/83] and 77% [64/83], respectively, 95.1% LCL 0.038). The intent-to-treat missing = failure analysis showed comparable results. Changes in CD4⁺ cell count from baseline, overall mean self-reported adherence (Trizivir 97%, Combivir-ABC 92%), and adverse events did not differ significantly between treatments. No ABC-related hypersensitivity reactions occurred. Conclusion. Trizivir was clinically equivalent to Combivir-ABC and may be substituted for the latter to simplify treatment and reduce pill burden.