Preliminary results of a company study to evaluate the effects of Manoplax showed that heart patients receiving a dosage of 100mg a day had a significantly increased risk of death compared with those not taking the drug.
Boots said it had not discovered a similar trend among patients taking 75mg a day. Its study of Manoplax would continue at this lower level and the company, after discussions with the regulatory authorities in the US and the UK, was advising doctors prescribing the drug to reduce dosage below 100mg a day.
Shares in Boots, which has invested more than pounds 55m in Manoplax and has spent pounds 20m marketing the drug in the financial year ended last month, fell back sharply on the news, closing 29p lower at 464p.
Although Boots said yesterday that it had every confidence in the prospects for Manoplax, analysts regarded the news as a noticeable setback. Nigel Barnes, a pharmaceuticals analyst at Hoare Govett, said: 'This news has effectively destroyed the image of the drug. Even if Manoplax is not pulled, its marketing becomes hugely difficult since competitors will be quick to alert doctors to the study's findings'.
Rodney Forrest, retailing analyst at Credit Lyonnais Laing, said: 'Clearly it is a significant blow. But there is still considerable uncertainty about the precise significance of this new information.'
Manoplax is used to treat congestive heart failure in patients who have not responded to or cannot tolerate other forms of therapy such as ACE- inhibitors. The drug aims to improve quality of life by reducing fatigue and breathlessness.
The stock market has seen Manoplax as vital to the future of Boots' pharmaceutical division, which has no other significant products in the pipeline.
Before the latest news, analysts had been tentatively forecasting sales for Manoplax of between dollars 250m ( pounds 160m) and dollars 300m by the late 1990s and operating profits of more than dollars 100m. Boots launched Manoplax in the UK last September, following approval from the Department of Health, and began selling it in the US last month.
Boots said that results to date of its study of the effects of Manoplax, conducted among 3,500 patients in Scandinavia, Canada and the US, had not been completely analysed. It would be some weeks before a further announcement could be made.
In September 1989 Boots said that US clinical trials had shown no statistically significant difference compared with a placebo. Later re-calculations modified these findings.
Boots is expanding further into Continental European healthcare with the purchase of a French and an Italian company for a combined pounds 14.5m. La Societe Francaise du Triclocarbon produces a shaving foam for sensitive skins and medicated washes with annual sales of pounds 5.1m. Marco Viti, based near Milan, supplies a wide range of over-the- counter products with sales of pounds 4.4m. Both companies' products complement Boots' core areas.Reuse content