The survival rate among nearly 5,000 AIDS victims who took the drug once know as AZT was much higher than among others who did not take it, say researchers for the medicine's maker. The finding confirms the life-saving potential of zidovudine, which is sold under the brand name Retrovir, said a Duke University physician independent of the study group. Researchers enrolled 4,805 patients who had suffered from pneumonia, common in people with AIDS, and treated them with zidovudine, the only AIDS-fighting medication approved by the federal government. Seventy-three percent of the subjects were still alive about 10 months after treatment started.