GlaxoSmithKline has £9.8bn wiped off its market value

An American medical journal will this week publish a major study that GlaxoSmithKline says will back up its fierce defence of Avandia, its diabetes treatment whose safety has been called into question.

The results of the GSK-commissioned study of 30,000 diabetes patients in a real-world setting, to be published as soon as tomorrow, is expected to show that Avandia has a safety profile similar to rival treatments. The FTSE 100 drug giant hopes that will mean a reprieve after a horrid two weeks, in which it has seen 11.8 per cent of its market value, or £9.8bn, wiped away.

The identity of the American publication was being closely guarded this weekend because of fears that it would be inundated with calls if it was revealed. The public interest in the case is high. Avandia was approved by the US Food and Drug administration in 1999 and is taken by thousands of patients. Last year it generated £1.6bn in sales.

Its safety has come into doubt since The New England Journal of Medicine published a study on 21 May that said that Avandia users were at greater risk of heart attack. Steven Nissen, the chairman of cardiovascular medicine of the Cleveland Clinic in Ohio, found that Avandia users were 43 per cent more likely to suffer a heart attack and 64 per cent more likely to die due to heart complications. Dr Nissen admitted that his meta-analysis was not comprehensive and required further study. GSK has fiercely defended the drug. Ronald Krall, GSK's chief medical officer, published a letter last week in The Lancet citing other studies that he argued proved its safety. Investors fear that the company will have to pay out billions in damages and that sales of its second-best-selling drug will drastically decline. The FDA said it will assemble a group of experts to review the drug.

Further reading: Read 'Hard Sell: The Evolution of a Viagra Salesman' for the inside story of drug company sales wars