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N Engl J Med. 1996 Oct 10;335(15):1081-90.

A trial comparing nucleoside monotherapy with combination therapy in HIV-infected adults with CD4 cell counts from 200 to 500 per cubic millimeter. AIDS Clinical Trials Group Study 175 Study Team.

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  • 1Harvard Medical School, Boston, MA 02215, USA.



This double-blind study evaluated treatment with either a single nucleoside or two nucleosides in adults infected with human immunodeficiency virus type 1 (HIV-1) whose CD4 cell counts were from 200 to 500 per cubic millimeter.


We randomly assigned 2467 HIV-1--infected patients (43 percent without prior antiretroviral treatment) to one of four daily regimens: 600 mg of zidovudine; 600 mg of zidovudine plus 400 mg of didanosine; 600 mg of zidovudine plus 2.25 mg of zalcitabine; or 400 mg of didanosine. The primary end point was a > or = 50 percent decline in the CD4 cell count, development of the acquired immunodeficiency syndrome (AIDS), or death.


Progression to the primary end point was more frequent with zidovudine alone (32 percent) than with zidovudine plus didanosine (18 percent; relative hazard ratio, 0.50; P<0.001), zidovudine plus zalcitabine (20 percent; relative hazard ratio, 0.54; P<0.001), or didanosine alone (22 percent; relative hazard ratio, 0.61; P<0.001). The relative hazard ratios for progression to an AIDS-defining event or death were 0.64 (P=0.005) for zidovudine plus didanosine, as compared with zidovudine alone, 0.77 (P=0.085) for zidovudine plus zalcitabine, and 0.69 (P=0.019) for didanosine alone. The relative hazard ratios for death were 0.55 (P=0.008), 0.71 (P=0.10), and 0.51 (P=0.003), respectively. For zidovudine plus zalcitabine, the benefits were limited to those without previous treatment.


Treatment with zidovudine plus didanosine, zidovudine plus zalcitabine, or didanosine alone slows the progression of HIV disease and is superior to treatment with zidovudine alone. Antiretroviral therapy can improve survival in patients with 200 to 500 CD4 cells per cubic millimeter.

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