More than 10,000 patients may be dying every year because of adverse reactions to drugs prescribed to treat ailments such as heart disease and arthritis, a study indicates.

Daily low-dose aspirin taken to counter heart disease, warfarin and other non-steroidal anti-inflammatory drugs (NSAIDs) and diuretics were the most common medicines implicated.

Aspirin and other NSAIDs can cause bleeding of the stomach, and diuretics, prescribed to counter fluid retention in heart disease, can lead to dangerously low potassium levels.

The problem is highlighted in the British Medical Journal which publishes a theme issue today on the harm caused by medicine. Very few people attend a doctor thinking they may come out worse than when they went in, but many do, it says. Overall, patients have a one in 10 chance of suffering an adverse event on being admitted to hospital and a one in 100 chance of dying as a result. The BMJ examines how the harms caused by medicine can be balanced against the benefits.

Doctors from the University of Liverpool, who monitored almost 19,000 patients admitted to two NHS hospital in Merseyside over a six-month period, found one in 16 (1,225) were for adverse drug reactions. On average they remained in hospital for eight days. Most patients recovered but 28 (2.3 per cent) died as a result of the interaction. Extrapolating these figures to the whole UK, the researchers say adverse reactions causing hospital admission account for 5,700 deaths a year. When those occurring in hospital are included, the total "may turn out to be greater than 10,000 a year", the researchers write.

In addition to the suffering to patients, the problem also imposes a burden on the NHS with affected patients accounting for 4 per cent of hospital bed capacity at a cost of £466m.

The study's authors include Alasdair Breckenridge, chairman of the Medicines and Healthcare Products Regulatory Agency, responsible for the safety of drug prescribing in the UK. The authors say "most adverse reactions were predictable from the known pharmacology of the drugs and many represented known interactions". They caution that the drugs have benefits, as well as causing harm.

There is a wealth of evidence that low-dose aspirin can prevent heart attacks over the long term in patients at high risk. But the authors say more should be done to avoid adverse reactions. "It is incumbent on prescribers to determine the need for a particular drug in a patient and to use this drug at the lowest dose necessary to achieve benefit." They add: "Many [adverse reactions] may be preventable through simple improvements in prescribing and are therefore likely to be preventable. Measures are urgently needed to reduce the burden on the NHS." The Medical Defence Union said drug errors accounted for a quarter of the claims against GPs on which it paid out, costing £12.5m over five years. Many errors could be avoided by having systems in place to review repeat prescribing, better monitoring of patients on long-term medication and ensuring that when adverse reactions occurred lessons were learnt.

Karen Dalby, MDU clinical risk manager, said it was unclear how many of the patients in the BMJ study had been prescribed drugs by their GP. She added: "But our research shows that GPs have a key role to play in protecting patient safety and helping avoid many preventable drug errors.

"When you consider that the average GP prescribes around 15,000 items a year, it is perhaps not surprising that errors do occasionally occur. But by learning from adverse events doctors can put systems into place to prevent the same thing happening to another patient."


Anti-inflammatory drugs (29.6% of adverse reactions)

Non-steroidal anti-inflammatory drugs include aspirin, diclofenac, ibuprofen and rofecoxib. They are prescribed for heart disease to reduce clotting of the blood, and as painkillers, especially in arthritis. They can cause gastro-intestinal bleeding, peptic ulcers, bleeding in the brain, kidney problems, wheezing or a rash.

Diuretics (27.3% of adverse reactions)

Diuretics such as furosemide, bendroflumethiazide, bumetanide and spironolactone are prescribed for heart disease and other conditions associated with fluid retention to increase urine production.They can cause kidney problems, low blood pressure, electrolyte disturbances and gout.

Warfarin (10.5% of adverse reactions)

Prescribed for heart disease to thin the blood. It can cause gastro-intestinal bleeding, blood in the urine and bruising.

ACE inhibitors (7.7% of adverse reactions)

ACE inhibitors such as ramipril, enalapril and captopril are prescribed for heart disease. They can cause kidney problems, low blood pressure and electrolyte disturbances.

Anti-depressants (7.1% of adverse reactions)

Antidepressants include fluoxetine, paroxetine and amitriptyline. They are prescribed for depression. They can also cause confusion, low blood pressure, constipation and gastro-intestinal bleeding.

Other drugs causing adverse reactions include beta blockers for high blood pressure, opiates to treat severe pain, and steroids to treat inflammation.