Bayer’s Trasylol product, used to stop bleeding in patients undergoing open-heart surgery, more than doubles the risk of kidney failure, according to a study published in the New England Journal of Medicine.

The authors say this risk is too high and have called for a block on the use of Trasylol (aprotinin) in these patients. Bayer is also carrying out trials of Phase III Trasylol in other surgical procedures, such as hip replacements and spinal-fusion operations.

The study is a blow to Bayer, which counts Trasylol among its fastest-growing products and has been investing in a marketing campaign to boost the brand, first approved in the USA in 1993. These efforts have started to pay off, with a 36% increase in revenues for the drug in the first nine months of 2005 to 164 million euros ($200m). It is sold in 60 countries around the world.

The NEJM study included 4,374 patients undergoing bypass surgery between 1996 and 2000, who were given Trasylol or two other drugs used to inhibit blood loss, aminocaproic acid or tranexamic acid, which are both available as generics.

Patients receiving Trasylol were 2.6 times more likely to develop kidney failure than those receiving the generics, prompting the authors to suggest that that doctors stop using Trasylol and switch to the alternative drugs. Trasylol also associated with an increased risk for heart attacks and strokes.

Bayer said it had not yet had the chance to fully review the findings but said in a statement they were "not consistent with the more than 15 years of clinical data and experience Bayer has amassed on this drug."