Caution over use of AZT to protect foetus: Researchers warn that it can take years to monitor the long-term effects of anti-Aids drug on pregnant women

AIDS RESEARCHERS reacted cautiously yesterday to American approval for the use of the drug AZT in pregnant women infected with the virus, after early trials suggested that it prevented transmission to the foetus.

A study presented at the 10th International Conference on Aids in Yokohama, Japan, concluded that AZT reduced the risk of maternal transmission by up to two-thirds. On the same day the American Food and Drug Administration (FDA) approved the drug for prevention of mother-to-child transmission. British approval is likely before the end of the year; at present it is given to pregnant women who have Aids, and not as a means of protecting the child.

The American decision will trigger an ethical debate about mandatory testing for pregnant women, and how AZT, if effective, could be made available in Africa and Asia where it is most needed. Other methods of reducing HIV transmission, such as Caesarean sections and bottle feeding, are also impractical for these countries. It is not known how many babies are infected by their mothers: figures range from 15 per cent to 30 per cent. More than 2 million children have been infected since the start of the pandemic.

James Balsley, of the Aids division of the US National Institutes of Health, which took part in the study, said yesterday: 'The study is still on-going. It can take years to monitor the long-term effects.' He added that the treatment was too costly to be used in the Third World.

Yvonne Bryson, professor of paediatrics at the University of California, Los Angeles, said that, although the drug seemed well-tolerated in mothers and children, 'what we are saying today may not be true in several years'.

Five years ago, an American trial of AZT (also known as zidovudine) in delaying the onset of Aids was halted amid worldwide publicity. The drug appeared to greatly enhance survival and it was deemed unethical to continue with a trial in which only half of the patients were on AZT and the rest had a placebo pill. However, the Concorde trial, a longer-running British/French initiative, last year showed the advantage conferred by AZT was short-lived.

Meanwhile Wellcome, manufacturers of the drug which accounts for about 12 per cent of its pounds 2bn annual sales, has been seeking to promote its use in HIV-positive pregnant women. In a new trial involving 477 women and 421 infants in the US and France, the women were given the drug orally after the first trimester, and then as an infusion during labour. Some of the babies were given AZT syrup. The American arm of this trial was halted in February for ethical reasons. Preliminary results suggested that AZT cut the incidence of transmission of HIV during pregnancy, at delivery and in the neonatal period from 25.5 per cent to 8.3 per cent.