Scientists call for caution in prescribing anticoagulants after some patients with other conditions found to suffer more strokes

Blood-thinning drugs may increase rather than cut the risk of stroke in some people over 65 who have an irregular heartbeat and also chronic kidney disease, according to a new study.

The researchers are calling on doctors to be more cautious in prescribing the drugs, called anticoagulants, until there has been more research.

Research led by scientists at University College London highlights the problems with polypharmacy – the use of multiple drugs for people with more than one health issue. Older people are especially likely to be on medication for more than one complaint.

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The researchers enrolled nearly 7,000 patients who had chronic kidney disease and were then diagnosed with atrial fibrillation – the most common form of irregular heartbeat. It affects at least 33.5 million people over the age of 55 worldwide and accounts for 1% of the NHS health budget in the UK.

Chronic kidney disease is also common, says the paper in the British Medical Journal, affecting 10-15% of adults. A third also have atrial fibrillation. About half a million people in the UK have both conditions and could be prescribed blood-thinning drugs.

The researchers monitored the participants, half of whom were on blood-thinning drugs and half not, for 506 days. They found those on the medication were 2.6 times as likely as those not on anticoagulants to have a stroke, and 2.4 times as likely to have a haemorrhage. There was not, however, an increased risk of death.

“We found that in this particular group, their medication seems to do the opposite of its intended effect,” said the study’s first author, Dr Shankar Kumar of the UCL Centre for Medical Imaging.

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“As we found a paradoxical reduced mortality rate alongside increased rates of stroke and major bleeding, this is clearly a very complex area. We strongly call for randomised controlled studies to test the clinical value and safety of anticoagulant drug therapy for people with both atrial fibrillation and chronic kidney disease,” said Kumar.

The Medicines and Healthcare Products Regulatory Agency, which licenses drugs, said it was aware of the study “and will review the findings to determine whether they have any implications for the safe use of these medicines. Any patient who is concerned about their treatment with blood thinners should contact their doctor but continue to take their medicine in the meantime.”