High doses of aspirin may also be given immediately after an acute heart attack; these doses may inhibit the synthesis of prothrombin and therefore produce a second and different anticoagulant effect, although this is not well understood.
The main undesirable side effects of aspirin are gastrointestinal distress—including ulcers and stomach bleeding—and tinnitus, especially in higher doses. Another adverse effect is increased bleeding in menstruating women, due to aspirin's anticoagulant properties. In children under 12 years of age, aspirin is no longer used to control flu-like symptoms or the symptoms of chickenpox, due to the risk of Reye's syndrome.
Aspirin was the first-discovered member of the class of drugs known as non-steroidal anti-inflammatory drugs (NSAIDs), not all of which are salicylates, although they all have similar effects and most have some mechanism of action which involves non-selective inhibition of the enzyme cyclooxygenase.
Patients resistant to aspirin risk heart attack
Rebecca Smith 18/01/2008A quarter of patients who take aspirin do not respond to the drug, leaving them at greater risk of dying from a heart attack or stroke, scientists claim. A review has found patients who are resistant to the painkiller are four times more likely to have a heart attack, stroke, or blood clot. They are almost six times as likely to die from such an attack. They are also four times as likely to suffer acute coronary syndrome, which causes chest pain due to reduced blood flow to the heart, than patients who respond to aspirin.
Aspirin is one of the most widely taken drugs in the world, costing less than 5p per patient per day. It is used to prevent clotting in millions of people at risk of heart attacks, strokes and blood clots. Almost 28 million prescriptions for aspirin were written in England in 2006.
The research, published in the British Medical Journal, reviewed 20 studies involving almost 3,000 patients and found 28 per cent were aspirin resistant. The work by a team in Toronto, Canada, found that patients who did not respond to aspirin did not respond to other similar drugs either. It is not clear why this is, and there is no simple test to establish which patients are resistant to aspirin, the authors said.
The lead author, George Krasopoulos, a cardiovascular surgery fellow, said: "It is unclear whether these patients simply receive too low an aspirin dose, are not compliant, have differing abilities to absorb aspirin, or have an underlying genetic disposition that renders aspirin ineffective." Mr Krasopoulos calls for further research. Until then he advises that "doctors continue their current practice in prescribing aspirin".
In an accompanying article, Giuseppe Biondi-Zoccai, the assistant professor in cardiology, at the University of Turin, and Marzia Lotrionte, the consultant cardiologist, at Catholic University in Rome, said drug companies might be keen to reduce aspirin's leading role in cardiovascular disease.
The firms could "substitute it with much more expensive but marginally more effective alternatives", they say.
Mike Knapton, the director of prevention and care at the British Heart Foundation, said: "For most people aspirin is a safe and effective treatment that can save lives by preventing heart attacks and strokes. "This study shows that some people may not be gaining as much benefit from taking aspirin as others. This is thought to be due to a 'resistance' to aspirin, but there is no accepted gold standard test to define aspirin 'resistance'. "Patients being prescribed aspirin should talk to their doctor if they are concerned about their medication."
See also
Women and heart disease
What men should eat every day
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