FDA Committee Recommends New AIDS Drug : Health: Scientists ask government to approve Stavudine, or d4T, after some success in clinical studies. But panel urges caution regarding its risks.

A panel of scientists recommended Friday that the federal government approve a new drug to battle the AIDS virus--but with strong warnings that doctors still don’t know enough about the medicine to say who should take it.

An advisory committee to the Food and Drug Administration said Stavudine, or d4T, probably provides some benefit over the three existing AIDS drugs. But the panel couldn’t say just who would benefit, just how safe it was or whether the manufacturer was on the right track to answer the many questions.

“I’m not sure how good our advice was today,” said Dr. Deborah Cotton, a Harvard University professor who chaired the panel.

The FDA is considering whether to permit the sale of d4T under a special procedure that allows promising drugs for life-threatening diseases on the market before their makers prove definitively that they work. Permission could be revoked if the drug maker fails to meet the FDA’s conditions.

The FDA has not said when it will decide on d4T. It is not bound by the advisory board’s decisions, but generally follows them.

Bristol-Myers Squibb says d4T appears to help raise the immunity of people with the human immunodeficiency virus while causing fewer side effects than other AIDS drugs.

Currently, there are three approved AIDS drugs, AZT, or Zidovudine; ddI, or Didanosine; and ddC, or Zalcitabine. Each works by blocking the action of an enzyme called reverse transcriptase that the virus uses to replicate.

All cause fairly severe side effects, and the virus can mutate to resist them. Some patients experience resistance to AZT, the most widely used drug, as soon as six months after starting treatment.

Officials said d4T works in a similar manner.

But there are major unsettled questions about the new drug: Who will it benefit? Are there short-term benefits? Does it increase AIDS patients’ survival? Are there fewer side effects, as the manufacturer claims?

The company asked the FDA to approve d4T for AIDS patients who cannot take any of the other drugs because of serious side effects or drug resistance.

It has studied 10,000 such people, giving them two different doses of d4T. After a year and a half, 79% are still alive, but 21% have experienced some peripheral neuropathy, a painful nerve disorder, which some critics called an unacceptable risk.

But the study, still incomplete, could not prove whether the neuropathy was caused by d4T or by AIDS. It indicated that a lower dose of d4T--20 milligrams twice a day--poses less of a risk of neuropathy. But the advisory committee said that evidence was troubling because the patients in another study who had the best benefits needed 40 milligrams twice a day.

The advisory committee said the best test given so far was in 359 patients who had taken AZT for six months. Half were given d4T and the rest continued taking AZT. Preliminary data shows those on d4T had a very small increase in CD4 cells, the body’s master immune cell.

The increase--though only about 20 to 25 cells per milliliter of blood--was significant because the AZT patients saw their CD4 cells continuously drop.

The d4T patients also experienced a small weight gain and told the company through questionnaires that they felt some improvement in quality of life.

“It just might be that this drug is a better drug than Zidovudine . . . but we haven’t seen any data to prove that,” said Dr. Paul Lietman, an advisory committee member and professor at Johns Hopkins University.

Some AIDS activists said there are still too many unanswered questions about d4T.

“We don’t know how or when or if to use this drug,” said Derrick Link of Gay Men’s Health Crisis.

The scientists agreed. They urged Bristol-Myers to study how d4T will interact with other AIDS drugs--because patients commonly take more than one--and how it will interact with drugs they need for tuberculosis and other AIDS-related infections.

They told Bristol-Myers to study d4T in children, women and minorities because the studies to date are primarily in young white men.