Adjusting for Differential Rates of Prophylaxis Therapy for PCP in High-Versus Low-Dose AZT Treatment Arms in an AIDS Randomized Trial

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Abstract
In the AIDS Clinical Trial Group randomized trial 002 comparing the effect of high-dose versus low-dose 3-azido-3-deoxythymidine (AZT) on the survival of acquired immunodeficiency syndrome (AIDS) patients, the median survival in the low-dose arm exceeded that in the high-dose arm. But subjects in the low-dose AZT arm received significantly more prophylaxis therapy for pneumocystis carinii pneumonia (PCP), a nonrandomized treatment, than those in the high-dose AZT arm. Thus the improved median survival in the low-dose arm might represent either the benefits associated with avoiding the toxicity of high-dose AZT therapy or the benefits of receiving prophylaxis therapy. The authors use structural nested failure time (SNFT) models to estimate the survival curves that would have been observed if the PCP prophylaxis experience in the high-dose and low-dose treatment arms had been similar. Our simplest models relate a subject's observed time of death and observed prophylaxis therapy to the time that the...