More than 10,000 patients a year may be dying because of a bad reaction to common medications such as aspirin, anti-depressants and blood-thinning drugs, new research suggests.

A study has found that adverse drug reactions (ADRs) to medicines accounted for one in 16 hospital admissions, costing the NHS an estimated £466 million a year.

Researchers, writing in the British Medical Journal, called for urgent measures to reduce the burden on the NHS and improve prescribing practices.

The scientists, based at the University of Liverpool, studied 18,820 patients, aged over 16, who were admitted to two NHS hospitals in Merseyside during a six-month period in 2001-02.

The patients were assessed to find out whether their admission to hospital was due to a reaction to their drugs.

The team found that 1,225 admissions (6.5 per cent) were related to adverse drugs reactions, with an average stay of eight days - accounting for 4 per cent of hospital bed capacity.

Most of the patients recovered, but 28 (2.3 per cent) died because of the reaction - most from gastrointestinal bleeding caused by aspirin or a reaction between aspirin and another drug.

Aspirin, which is often prescribed to patients to avoid heart disease, was most commonly implicated - accounting for 18 per cent of the admissions.

Other drugs which caused a bad reaction included the anti-clotting drug warfarin, non-steroidal anti-inflammatory drugs (NSAIDs) and diuretics, used to treat fluid retention, given to people with kidney and heart disorders and used to treat high blood pressure.

But the researchers estimated that three-quarters of the ADRs were "definitely" or "possibly" avoidable with better prescribing patterns.

The team, led by Professor Munir Pirmohamed, said that it was possible that at any one time up to seven 800-bed hospitals may be occupied by patients admitted because of reactions to their drugs.

They also estimated that ADRs causing hospital admission were responsible for the deaths of 5,700 patients a year in England.

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