Laboratory tests show a potential AIDS drug may be as powerful as AZT, the only government-authorized drug to fight the AIDS virus, while producing fewer side effects, researchers said.

Researchers from University of Massachusetts Medical School in Worcester, Mass., and Boehringer Ingelheim Pharmaceuticals in Ridgefield, Conn., said Thursday they hope to begin testing the promising compound on humans early next year.Scientists found the drug, dubbed B1-RG-587, while screening about 1,000 substances for those that would knock out reverse transcriptase - an enzyme that the AIDS virus needs to multiply - while leaving similar enzymes in human cells unharmed.

The current standard therapy for AIDS, zidovudine or AZT, blocks reverse transcriptase but also damages similar enzymes in human cells, creating serious side effects like bone marrow suppression. Other experimental drugs in widescale testing, DDI and DDC, act in the same fashion as AZT and produce side effects like pain in the nerve endings and potentially fatal inflammation of the pancreas.

"The significant difference of this compound from AZT is that unlike AZT, it is not capable of inhibiting normal cell growth," said Alan Rosenthal, head of research at Boerhinger Ingelheim and co-author of the study published in the journal Science.

In tests on rodents, monkeys and chimpanzees, oral doses of B1-RG-587 did not suppress bone marrow or cause other serious side effects at levels expected to be used in humans.