The results, which are only preliminary but are expected to reflect the final outcome of the trial, have set back the prospects of effective HIV treatment immeasurably.
Aids researchers had hoped that AZT, manufactured by the British company Wellcome, would be in the vanguard of other anti-viral drugs that could delay the onset of Aids considerably in HIV-positive people and thereby offer them the prospect of a longer life. Wellcome's shares fell 19p when news of the study reached the stock market.
A joint study financed by the British and French governments involving more than 1,700 participants who were followed over three years found that AZT, also known as zidovudine or Retrovir, was no better than a sugar pill at preventing the onset of Aids and death.
Ian Weller, a principal investigator on the Anglo-French 'Concorde' trial and a leading Aids researcher at the Middlesex Hospital in London, said yesterday that it is the 'most powerful study that has been carried out' into the effects of AZT on healthy carriers of HIV.
'The results are not encouraging as far as early intervention is concerned for asymptomatic people,' he said.
Nick Partridge, chief executive of the Terrence Higgins Trust, an Aids charity, said the results of the trial are 'very depressing' for people who have HIV and are well. 'It shows the need for increased research because we know now that AZT is unlikely on its own to halt progression of the disease. It shows the very limited nature of the treatments currently available. It is clear that we're many, many years away from adequate treatments and even further away from a vaccine.'
In a letter to the Lancet, the Concorde researchers say there is no difference in survival rates or chances of developing Aids between the 877 patients in the study who took AZT and the 872 who received a placebo.
After three years, 92 per cent of the AZT group were still alive, compared with 93 per cent survival in the placebo group. In both groups, 18 per cent had gone on to develop Aids. Side-effects were significantly more common in the AZT group.
The study, which began in October 1988, was organised jointly by the British Medical Research Council and the French National Aids Research Agency. Clinics in the UK, the Irish Republic and France took part and neither patients nor doctors knew whether they were taking a placebo or AZT, a 'double blind' precaution that scientists use to ensure that a bias is not inadvertently introduced.
Dr Weller, who questioned the early use of AZT when smaller clinical trials in the US suggested it could benefit HIV-positive people, said there is no benefit to healthy HIV- positive people in receiving AZT.
'I think we have to wait for the full results to be pubished to judge its effect on clincal practice,' he added.
Dr Weller said that it was always difficult to decide when to begin treatment with AZT, which produces side-effects in some people. The results do not, he said, affect the benefits of giving the drug to people with Aids, who can extend their lives by an average of about nine months or more with treatment.
'I think for people who were uncertain (about when to begin taking AZT), there is going to be more uncertainty. I think people who were waiting for the early symptoms to appear will be more sure they are doing the right thing.'
Wellcome earns more than pounds 200m a year from selling the drug to more than 200,000 people worldwide, most of whom have Aids or the early symptoms of the disease.
A spokesman for Wellcome said the company took exception to the conclusions being drawn from the Concorde study.
He said the company, which has co-operated in the study, suggested alterations to the Lancet letter, but these were refused.
'We agreed to disagree. There are a lot of HIV-positive patients who are being told the drug doesn't work. That's simply not acceptable.'
Dr Weller said that the Concorde trial did identify a short-term benefit to patients in the early stages of the study, as other studies have done, but that did not last.
In 1989, an American trial of AZT was stopped early because it appeared to delay the onset of Aids. It was considered unethical to continue prescribing placebos to patients. Wellcome's shares shot up, adding pounds 1.4bn to its stock market value.
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