Evaluation of Patients Who Have Not Had Success With Zidovudine

High-grade resistance to AZT has been detected in HIV isolates from approximately 25 percent of individuals with AIDS who received AZT for at least 1 year. To elucidate the clinical significance of in vitro AZT resistance, it is necessary to distinguish between clinical failure caused by AZT resistance and clinical decompensation caused by other factors. One hundred-twenty patients who have been receiving AZT for at least 1 year are randomized to 1) continue with AZT, 2) switch to treatment with didanosine at 1 of 2 doses, or 3) receive both AZT and ddI. Treatment is given for 16 weeks, with a possible extension to 32 weeks. Patients are followed at weeks 2, 4, 8, 12, and 16. For analysis purposes only, patients are stratified according to degree of susceptibility of HIV isolates to AZT.