AstraZeneca shares have taken a tumble after health regulators in the USA and in Canada revealed that they are conducting safety reviews of the blockbuster antiulcerants Nexium and Prilosec, even though findings thus far suggest that the drugs do not increase the risk of heart trouble.

The process began at the end of May when AstraZeneca sent the US Food and Drug Administration, and other regulatory authorities worldwide, a preliminary review of new data from two small long-term clinical studies of Nexium (esomeprazole) and Prilosec (omeprazole) in patients with severe gastroesophageal reflux disease (GERD). Patients were randomised to receive either drug or to have surgery to control their GERD and the results from the 14-year study of Prilosec and five-year analyses from an ongoing study of Nexium “raised concerns that long-term use” of both drugs “may have increased the risk of heart attacks, heart failure, and heart-related sudden death...compared to patients who received surgery”, the FDA stated.

However the agency went on to state that AstraZeneca has provided it with additional data since then, and the FDA's “preliminary conclusion is that the observed difference in risk of heart attacks and other heart related problems seen in early analyses of the two small long-term studies is not a true effect". The agency added that it “does not believe that healthcare providers or patients should change either their prescribing practices or their use of these products at this time”, noting that it plans to complete its review within three months.

Meantime, Health Canada announced that it too has also launched a safety review of Nexium and Prilosec and its comments echoed those of the FDA. The regulator said that its own preliminary review “suggests that the evidence provided does not confirm the existence of a possible cardiovascular risk” and its analysis of the new information should be done by the end of the year.

However the problem lies in those dreaded words ‘safety review’ and AstraZeneca shares on the London Stock Exchange fell 3.5% to close at £24.30. The company is saying that patients have nothing to worry about but the uncertainty caused by these reports could cause damage to Nexium which had six-month sales of $2.6 billion, up 4%. Prilosec is sold over-the-counter by Procter & Gamble.