The anti-AIDS drug AZT (Retrovir) is suddenly being pushed as a treatment for preventing HIV-positive mothers from passing on the condition to their unborn children.

This new approach follows hard on the heels of the Concorde trials that showed the drug did not delay the onset of AIDS among HIV-positive people.

And as happened with the launch of the drug, the clinical trials among pregnant women have been stopped early because preliminary findings have been so positive.

AZT, also known as zidovudine, manufactured by Burroughs Wellcome, came on to the market in 1987 and was rushed through usually stringent US trials in just 20 months, so beneficial was it believed to be.

But the exhaustive Concorde trials, which ran from 1988 to 1991 and which compared the progress of 877 HIV patients given AZT against 872 given a placebo, showed that AZT had little or no effect in slowing the disease. Both groups showed a rate of progression to full blown AIDS and/or death of 18 per cent (The Lancet, 9 April 1994).

While Burroughs Wellcome, the American arm of Wellcome in the UK, never claimed the drug originally developed in 1963 to fight cancer could cure AIDS, the company said it would slow the progression of HIV by reducing the rate of duplication. Alarming side effects were reported, and Wellcome was criticized for selling the drug for £128 per 100 capsules, far above the usual price for drugs. Profits rocketed as did the share price, from 73.5p to 374.5p in 1987 when the drug was launched.

Despite the major setback of the Concorde findings, HIV-positive pregnant women are now being targeted for the drug following a 59 centre study. The study, by the US National Institutes of Health and the French Agence Nationale de Recherches sur le SIDA, claims the drug can reduce by two thirds the chances of women transmitting the virus to their unborn child.

The trial was stopped early when researchers found the transmission rate among mothers given 100 mg doses, five times a day of AZT was just 8.3 per cent against 25.5 per cent in the group given a placebo (BMJ, 5 March 1994 and JAMA, 16 March 1994).

Despite abandoning the trials prematurely, researchers are still concerned about the possible long term effects of the treatment.

In the US, AIDS is the fifth commonest cause of death among children under the age of 15.

l Researchers have located yet another virus, human herpesvirus 6 (HHV-6), which is found in AIDS sufferers (Lancet, 5 March 1994). The virus was isolated in a laboratory in 1986, and researchers at the National Cancer Institute at Bethesda, Maryland, first noted that HHV-6 could contribute to the depletion of CD4 T cells in AIDS patients about five years ago.