A dose-ranging study to evaluate the safety and efficacy of abacavir alone or in combination with zidovudine and lamivudine in antiretroviral treatment-naive subjects.

OBJECTIVE

To compare antiretroviral efficacy, safety and tolerance of three dosing regimens of the novel nucleoside reverse transcriptase inhibitor, abacavir (1592U89) over 24 weeks and its efficacy in open-label combination with zidovudine and lamivudine.

DESIGN

Sixty HIV-1-infected antiretroviral therapy naive subjects (entry criteria; CD4+ cell count > or = 100 cells/mm(3), plasma HIV-1 RNA > or = 30 000 copies/ml), randomized into 20 subjects per cohort received 100, 300 or 600 mg abacavir twice daily. Subjects successfully completing 24 weeks' randomized therapy could switch to open label therapy (abacavir, zidovudine, lamivudine at 300, 300 and 150 mg twice daily, respectively) for a further 24 weeks of studly, as could subjects meeting one or more switch criteria.

METHODS

Subjects were assessed for antiretroviral activity by measuring changes in plasma HIV-1 RNA load and CD4+ cell counts. Evaluation of safety and tolerance was based on clinical adverse events and laboratory analyses.

RESULTS

At week 4, subjects receiving 300 or 600 mg abacavir twice daily had greater reductions in plasma HIV-1 RNA (median changes -1.55 and -1.61 log10) copies/ml, respectively); differences (P = 0.007 and P < or = 0.001, respectively) than subjects receiving 100 mg abacavir twice daily (median change, -0.63 log10 copies/ml). Differences between the 300 and 600 mg twice daily groups were not clinically or statistically significant. At 24 weeks, analysis showed a median change in plasma HIV-1 RNA of -0.70 and -1.30 log10 copies/ml in the 300 and 600 mg twice daily groups, respectively. During the open label phase in which zidovudine/lamivudine was added to 300 mg abacavir twice daily, a further median reduction in plasma HIV-1 RNA of 1.74 log10 copies/ml was seen. At 48 weeks pooled data from all abacavir-treated subjects showed a sustained reduction in plasma HIV-1 RNA of 2.8 log10) copies/ml; 65% and 43% of subjects had < or = 400 and < or = 50 HIV-1 RNA copies/ml, respectively, and a further median increase of 111 CD4+ cells/mm3 were seen. Abacavir was generally well tolerated with few clinically significant adverse events. Two subjects (3.3%) developed hypersensitivity reactions to abacavir. There were no differences between the groups with regard to serious adverse events.

CONCLUSIONS

In terms of antiretroviral therapy naive subjects, treatment with 300 or 600 mg abacavir twice daily was statistically superior to a 100 mg twice daily dose at 4 weeks. Combinations therapy containing abacavir-zidovudine-lamivudine was a highly effective antiretroviral regimen, resulting in substantial reductions in plasma HIV-1 RNA which may be comparable to combinations containing protease inhibitors. Abacavir was generally tolerated.