Background. The initially tested dose of zidovudine for the treatment of patients with advanced disease caused by the human immunodeficiency virus type 1 (HIV) was 1500 mg. Although this dose is effective, it is associated with substantial toxicity. Methods. To evaluate the efficacy and safety of a reduced dose, we conducted a randomized controlled trial in 524 subjects who had had a first episode of Pneumocystis carinii pneumonia. The subjects were assigned to receive zidovudine in either a dose of 250 mg taken orally every four hours (the standard-treatment group, n = 262) or a dose of 200 mg taken orally every four hours for four weeks and thereafter 100 mg taken every four hours (the low-dose group, n = 262). Results. The median length of follow-up was 25.6 months. At 18 months the estimated survival rates were 52 percent for the standard-treatment group and 63 percent for the low-dose group (P = 0.012 by the log-rank test). At 24 months the estimated survival rates were 27 percent for the standard-treatment group and 34 percent for the low-dose group (P = 0.033). In both groups, 82 percent of the subjects had another opportunistic infection, and the length of time to that infection was similar in the two groups (P = 0.56 by the log-rank test). CD4 T-lymphocyte counts improved transiently in both groups, and serum levels of HIV antigen decreased in the subjects with antigenemia. The hemoglobin level declined to less than 5 mmol per liter (80 g per liter) in 101 subjects in the standard-treatment group and in 77 in the low-dose group (39 vs. 29 percent, P = 0.0009 by the log-rank test). The neutrophil count declined to less than 0.750×109 per liter in 134 subjects in the standard-treatment group and in 96 in the low-dose group (51 vs. 37 percent, P = 0.0001). Conclusions. The reduced daily dose of zidovudine used in this study was at least as effective as the standard dose and was less toxic; however, with the use of a four-week induction period with a high dose followed by low-dose treatment, severe anemia and neutropenia were common complications of treatment with zidovudine.
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