A Randomized Controlled Trial of a Reduced Daily Dose of Zidovudine in Patients with the Acquired Immunodeficiency Syndrome

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. 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). 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 lowdose 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). 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. ZIDOVUDINE (3′-azido-3′-deoxythymidine; formerly azidothymidine, or AZT) is a thymidine analogue that inhibits the replication of the human immunodeficiency virus type 1 (HIV) in vitro.¹ The administration of zidovudine to patients with advanced HIV disease over a 6-to-24-month period prolongs survival, decreases the frequency and severity of opportunistic infections, improves neurologic function, transiently improves CD4 T-lymphocyte counts, and decreases the rate of HIV antigenemia.^{2 3 4 5 6 7 8} Despite these benefits, zidovudine therapy is frequently associated with adverse reactions, including both anemia and neutropenia.^2,9 Although the serum half-life of zidovudine is one hour, the intracellular half-life of its 5′-triphosphate form approaches three hours, suggesting that…