Heartburn pills like Nexium and Prilosec do not stop blood-thinning drugs such as Plavix from working effectively, contrary to recent fears, new research on Monday showed.

The finding is reassuring to patients, doctors and drug companies, including AstraZeneca and Sanofi-Aventis, who make the blockbuster treatments.

Plavix is the world's second biggest-selling medicine, with worldwide sales of around $9 billion, while Nexium revenues totalled $5.2 billion in 2008.

Plavix, also known as clopidogrel and sold by Sanofi and Bristol-Myers Squibb, is widely used with proton pump inhibitors, or PPIs, including AstraZeneca's Nexium and Prilosec to cut the risk of gastric problems.

A study in March raised concerns that mixing the two types of medicines increased the risk of heart patients having a second heart attack and led regulators on both sides of the Atlantic to issue warnings discouraging combined use unless essential.

But Michelle O'Donoghue of Boston's Brigham and Women's Hospital said a new analysis of a large clinical involving more than 13,000 patients taking Plavix or Eli Lilly and Daiichi Sankyo's new drug Effient, or prasugrel, showed they did not interfere with the heart drugs' clinical benefits.

'Use of a proton pump inhibitor was not associated with increased risk of cardiovascular events for patients on either clopidogrel or prasugrel,' she told the annual meeting of the European Society of Cardiology.

The most commonly used PPIs in the study were Prilosec and pantoprazole.

O'Donoghue's findings will be published in the Lancet medical journal on Tuesday.

Lars Wallentin of the Uppsala Clinical Research Centre in Sweden told doctors in Barcelona he had also seen no evidence of PPI-associated problems in a study involving more than 18,000 patients that compared Plavix and AstraZeneca's experimental drug Brilinta.

Cardiologists said the new analyses were encouraging. Many had worried that avoiding PPIs would lead to more gastrointestinal bleeding complications.

However, the issue will only be closed conclusively by conducting a large clinical trial focused specifically on interaction, said Kurt Huber, a cardiologist at Wilhelmine Hospital in Vienna.

'There seems to be no deleterious effect ... but we need a prospective randomised trial to definitely establish safety,' he told the meeting. 'As long as we don't have these data, careful selection of patients who need gastric protection should be performed.' – Reuters