IT HAS long been billed as the great hope for HIV sufferers the wonder drug AZT which, it is claimed, can slow the progression towards AIDS. Now its manufacturer, the Wellcome company, is facing a legal case that could blow apart a multi-billion-pound industry.

For Sue Threakall, however, whose husband died after taking AZT, a writ served on her behalf last week was more than an attempt to win damages. She said it represented a chance to end what may be a terrible medical blunder endangering thousands of lives.

Threakall, 40, a former deputy head teacher, has begun her legal action against Wellcome and the National Institute of Allergic and Infectious Diseases (NIAID), the United States government body that tested and promoted the drug.

Supported by legal aid, she is alleging there was a lack of care in the researching, marketing and prescribing of the drug which, she says, contributed to her husband's death. The writ is intended as the start of a group action in Britain, with co-ordinated litigation in other countries.

Threakall, from Birmingham, is convinced that far from helping her HIV-positive husband, Bob, a 47-year-old haemophiliac, AZT damaged his immune system so badly that even after he stopped taking it he went into an irreversible decline.

He tested positive for HIV in 1985, but continued working full-time as a civil servant for four years. He was also involved in a campaign to win compensation for haemophiliacs who had become HIV-positive as a result of treatment for their blood disorder. "He was gregarious, leading a full and busy life," Threakall said.

In August 1989 he was put on AZT, a toxic drug thought to be helpful in fighting HIV, which most doctors believe is the cause of AIDS. His wife believes the decision effectively ended his life.

A letter dated August 25 from the haemophilia unit where he was treated acknowledged that "this gentleman is feeling reasonably well" but added that "in view of the recent study concerning the beneficial effects of AZT in HIV-positive people" he had been started on daily doses.

The study mentioned was co-ordinated by NIAID in collaboration with Wellcome, whose sales of AZT totalled Pounds 270m last year. It was stopped early on the grounds that it had "clearly demonstrated" benefit, but its scientific validity has since been challenged.

A longer trial, conducted by government researchers in Britain and France, failed to find any benefit from AZT in HIV-positive people in fact, sickness and death were higher in the treated group. Detailed analysis of the study, due to be published in The Lancet next month, is expected to confirm this gloomy picture.

Threakall says her husband's health deteriorated from the time he was started on AZT. By December 1989 he was taking more time off work and did less of everything else. "Life here was absolute hell he was so miserable. I was trying to hold down my own job, but I gave it up the following summer because it was getting impossible to cope," she said.

"Our social life stopped. Bob changed from being a happy, gentle man to someone who didn't want anyone near him. It became a nightmare trying to feed him. I would make him a Marmite sandwich with the crusts taken off and he would spend an hour chewing it he became virtually anorexic. He was ashamed at being so thin."

At his request, the AZT treatment was stopped in July 1990. "I think it was too late," Threakall said. "He was so ill by then and so undernourished that he continued to go downhill."

She has since found that doctors have reported "worrying" evidence that blood and bone-marrow changes in long-term AZT treatment "seem not to be readily reversed when the drug is withdrawn".

He was admitted to hospital seven months later, where he died after three days "confused, delirious, wasted, constant diarrhoea, unable to swallow and with hardly any normal lung tissue left", according to his wife. His symptoms were attributed by doctors to HIV, although he was never diagnosed as suffering from full-blown AIDS.

The following April, after reading a report in The Sunday Times that a group of American scientists was challenging the theory that HIV causes AIDS, Threakall wrote to Dr Peter Duesberg, a professor of molecular biology at the University of California at Berkeley and leading member of the group.

Duesberg, who has described AZT as causing "AIDS by prescription", wrote back enclosing a package of material on AIDS and HIV that was to start Threakall on a journey of discovery that led to her decision to sue.

"I know I am right about what happened to Bob, and if the drug is toxic, what about all the other people who are taking it?" she said.

Her solicitor, Graham Ross, of JKeith Park and Co, in Liverpool, has received instructions in seven more cases. Six involve haemophiliacs and one is from a homosexual man suing over the death of his partner.

Ross said that he had become increasingly concerned about the death of Bob Threakall. "I have seen a lot that shows this case is strong. This would mean there has been a horror story in the treatment of HIV-positive individuals; and if there is a horror story, it will continue until the truth comes out."

Wellcome said it would defend the case. *

LINDSEY, 2 IN ORDEAL OF PAIN 

STEVE and Cheryl Nagel, from Minneapolis, are also planning to sue Wellcome. Their adopted daughter, Lindsey, was born in Romania in October 1990 and brought back to America that year. They found within a few weeks that she tested HIV-positive.

She was put on Retrovir syrup AZT, as marketed for children's use for 22 months. "By the grace of God, we determined that it was making her ill," Steve Nagel said.

For the first 18 months her health declined. She did not eat properly, suffered nausea and diarrhoea and became hyperactive. Then, for three months in 1992, the two-year-old "would wake up in the middle of the night grabbing her knees and screeching; she was in severe pain". They consulted Dr Peter Duesberg, who says HIV does not cause Aids, and he told them they should take Lindsey off AZT. "Two days later, the pains stopped, and have never come back since," said her father. *