The alarm was sounded by a study in the Netherlands that found that patients taking these drugs had nearly three times the risk of sudden cardiac death. The authors estimate that the drugs cause 320 deaths a year in the Netherlands. By extrapolation, that equates to 1,200 deaths a year in Britain and 15,000 deaths in Europe and the US as a whole.

The Dutch study, published in European Heart Journal, looked at all deaths between 1995 and 2003 in a population of half a million people from 150 general practices nationally for whom complete medical records are kept.

Those who had died of sudden cardiac death were compared with matched controls. The analysis showed that people using a range of different drugs, all known to influence the heart, were nearly three times as likely to suffer sudden cardiac death.

The drugs targeted in the study are those known to prolong the QT interval, the time the heart takes for its lower chambers to activate and deactivate. A long QT interval can lead to abnormal heart rhythm, poor contraction of the heart muscle and sudden death.

Many drugs are known to affect the QT interval. Among those included in the Dutch study, several have been withdrawn, discontinued or suspended in Britain. Cisapride, for example, used to treat heartburn, was suspended in 2000 by the Committee on Safety of Medicines after it had been linked with at least 125 sudden deaths around the world.

Bruno Stricker, the study’s senior author, from the Erasmus Medical Centre in Rotterdam, said that, although the findings were significant, it was important to keep them in proportion. It was normal to expect one or two sudden cardiac deaths per thousand of the population each year in Western countries. The risk for people taking the drugs rose to around three per thousand.

“These drugs are vital treatments for serious conditions in many cases, so it is essential that patients should not stop taking them on their own initiative,” Dr Stricker said. He said that the risk of sudden heart death was highest among those who had been on the drugs for less than 90 days. It was increased among users of gastro-intestinal medication and anti-psychotics, and the risk also tended to be higher among women than men and among older patients.

“Although prolongation of the QT interval by non-cardiac drugs is not an unusual finding, potentially fatal arrhythmias and sudden cardiac death are relatively uncommon,” Dr Stricker added.

Drug safety experts do not want to see valuable drugs withdrawn, particularly if there are no alternatives. They believe that identifying people at risk should make it possible to protect them better.

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