An experimental drug made from a Japanese fungus improves liver transplant patients' chances of survival by up to 20 percent over those taking standard anti-rejection medication, scientists report.

Transplant surgeon Thomas E. Starzl said recently that 23 University of Pittsburgh studies of FK-506 confirm earlier findings of its superiority over cyclosporine, the drug transplant patients must take for the rest of their lives to prevent their bodies from rejecting the donor organ.

Starzl, chief of the university's transplant program, told colleagues at a meeting of the International Congress of the Transplantation Society in San Francisco that FK-506 poses a lower risk of kidney failure and high blood pressure, common side effects of cyclosporine.

Both drugs prevent rejection of the transplanted organ immediately after the operation, but FK-506 also prevents delayed rejection, researchers said.

"Initial results are very encouraging," said John Armitage, assistant professor of surgery at Pitt, who conducted one of the studies. "There's no question that FK-506 is going to find its place in future treatment."

The university has given the drug to about 800 patients. The studies, conducted from February 1989 to June 1990, included the first look at how the drug worked in children. Doctors said high doses of steroids were unnecessary for 42 young patients who used FK-506. Some patients need steroids to reduce the toxicity of cyclosporine, but high doses can cause stunted growth, facial puffiness and other problems.

"With FK-506, we're hoping that these children will not require a second or third transplant," said Andreas Tzakis, an associate professor of surgery who conducted the study. "With the scarcity of organs available for children, this drug may result in organs available for a larger number of children."

But James Wolf, president of the United Network for Organ Sharing, said FK-506 could make more people eligible for transplants, creating pressure to find more donors. About 20,000 Americans are currently awaiting organ transplants.

The drug, made by Fujisawa Pharmaceutical Co. Ltd. of Osaka, Japan, has been approved for testing exclusively at the University of Pittsburgh, although in a few cases it has been given to patients at other hospitals. The drug must undergo further studies before the Food and Drug Administration approves its general use for liver transplant patients.

"There's no question it's a very effective drug for liver transplants," said Robert Corry, board member of the United Network for Organ Sharing. "We still don't know enough about it with other organs."

Ronald Lieberman, who directs an FDA team studying the drug, said approval will probably take at least two years.

In studies on liver transplant patients, the university reported:

18 percent of those taking FK-506 developed high blood pressure, compared with 60 percent of patients taking cyclosporine.

13 percent had kidney failure, compared with 26 percent for those on cyclosporine.

Potentially fatal infections occurred less frequently and were less severe in patients taking FK-506.