Scientists defended the practice of giving a single dose of the drug nevirapine to protect newborns from their mothers’ AIDS infections, saying on Thursday it works and is not toxic.

They found that adding other drugs to the dose helps even more and is safe for mother and baby.

Several studies presented to the conference show that adding a drug called Combivir to the nevirapine dose reduces mother-to-child transmission even more. Combivir, made by GlaxoSmithKline Plc, contains two HIV drugs called AZT and 3TC.

The use of nevirapine, made by German drugmaker Boehringer Ingelheim under the brand name Viramune, has become controversial. A single dose given to the mother as she goes into labor and to the baby at birth cuts the mother-to-child transmission of the AIDS virus by 47 percent. But in most women who get the drug, the virus mutates and appears to become resistant to nevirapine and perhaps also to other, related drugs.

“While people have been lauding this as a stunning breakthrough, others have said it represents a less-than-optimal regimen and we should not have subjected women in developing countries to this less than optimal approach,” said Dr. James McIntyre of the University of the Witwatersrand in Johannesburg, South Africa.

“In my country this has been seen as a U.S. and pharmaceutical company conspiracy,” McIntyre told the 12th Annual Retrovirus Conference, a meeting of AIDS researchers, in Boston. A U.S. National Institutes of Health researcher attacked the nevirapine studies as well, saying they were sloppily conducted and did not warn women of the risks of toxicity and resistance.

McIntyre said reports of liver toxicity come from people taking nevirapine over a long period of time, not in the single-dose patients.

NEED TO PROTECT BABIES

More than 39 million people around the world are infected with the fatal and incurable AIDS virus, and most of the new infections are now in women of childbearing age.

Nevirapine’s tendency to cause resistance raised fears that women who took the drug would have fewer options when their infection worsens and they need to begin taking the cocktails of drugs that can control the infection.

But Dr. Mary Glenn Fowler, head of perinatal prevention efforts at the U.S. Centers for Disease Control and Prevention, said there is no evidence that this is actually happening. “People have been making statements and there have been lots of opinions, but it is important to have the research to go on,” she said in a telephone interview.

Several teams said they showed giving various drug regimens protected babies, with no ill effects for the mothers.

A team at University Rene Descartes in Paris and at an AIDS treatment project in Abidjan, Ivory Coast, tested 329 pregnant women, giving them and their babies both Combivir and a single dose of nevirapine. “The six-week HIV transmission rate was 4.7 percent,” they told the conference.

Dr. Roger Shapiro of Beth Israel Deaconess Medical Center in Boston and colleagues tested more than 1,100 pregnant women, giving them AZT from 34 weeks gestation and giving the babies a month of AZT after birth. Half the women and babies at 4 sites in Botswana also got a single dose of nevirapine. Only 4.7 percent of the babies developed HIV infection. There was no real difference between the groups.

McIntyre and Fowler agreed that women must be given whatever drugs are available, from full drug cocktails if possible to a single nevirapine pill.

Activists defended the use of nevirapine. “There is absolutely nothing from a scientific vantage point to suggest that it will adversely affect a mother’s health,” said Mark Isaac of the Elizabeth Glaser Pediatric AIDS Foundation.