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RETROVIR TO VIDEX SWITCH REDUCES "AIDS-DEFINING" EVENTS

Executive Summary

RETROVIR TO VIDEX SWITCH REDUCES "AIDS-DEFINING" EVENTS by 33% in HIV-infected patients who have undergone AZT therapy for at least 16 weeks, James Kahn, principal investigator of a trial comparing the two agents, reported at an April 13 meeting of the National Institutes of Health AIDS Clinical Trial Group (ACTG). Patients enrolled in ACTG trial 116b/117 who were switched to 500 mg daily of ddI (Bristol-Myers Squibb's Videx) experienced "a 33% lower [AIDS-defining] event rate" than patients receiving comparable doses of AZT (Burroughs Wellcome's Retrovir), Kahn declared. Videx patients had "a statistically significant delay" in the onset of opportunistic infections and a "modest," but still statistically significant, increase in CD4 counts, Kahn said. Most of the benefit associated with switching to ddI appeared to occur among AIDS-related complex (ARC) patients, he noted. In patients with full blown AIDS, the performance of both drugs remained roughly "equivalent." A randomized, double-blind, placebo-controlled trial conducted at 43 medical centers throughout the country, 116b/117, compared the effects of two doses of ddI (500 mg and 750 mg daily) and one dose of AZT (600 mg daily) in persons with AIDS, ARC or asymptomatic HIV-disease. A total of 913 patients with CD4 counts between 0 and 300, who had received at least 16 weeks of prior AZT therapy, were enrolled in the trial. Although statistically significant benefits in the number of opportunistic infections and time to AIDS-defining events were observed in both ddI groups compared to AZT, Kahn noted that time to death and overall survival rates did not differ significantly between the three treatment arms. Kahn suggested that this might be the result of the study's follow-up procedures, which tracked patients and included them in the final statistical analysis even if they had "gone off study protocol" and begun taking different drugs. "Surprising[ly]" Kahn noted, the study also failed to differentiate among patients with varying durations of prior AZT therapy. The clinical benefit of ddI was the same in patients who received prior AZT therapy for four months or two years, suggesting that the development of AZT resistance was not a confounding factor in the trial results. Kahn and his co-presenter Stephen Lagakos concluded that further analysis is required to clarify the clinical significance of the 116b/117 results. Other studies examining the issue of resistance and the evaluation of surrogate markers in the trial currently are being planned, Kahn said. In addition, data from the study will be combined with the results of other ongoing clinical trials using ddI to form a larger data pool on the drug's efficacy. Videx is currently approved by FDA only as a second-line therapy for HIV-infection. FDA's Antiviral Drugs Advisory Committee is expected to review the results of the ACTG 116b/117 study when it meets the week of April 20 to discuss the approval status of ddI. FDA conditionally approved the drug on the basis of limited clinical data last fall ("The Pink Sheet" Oct. 14, 1991, p. 15).

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