nMRCGP exam update - Evidence for aspirin use

Contributed by Dr Louise Newson, a GP in the West Midlands.

Current situation

  • Many healthy people over the age of 50 years in the UK take regular aspirin.
  • Many patients at high risk of cardiovascular disease are still not taking aspirin.
  • Aspirin remains the most cost effective and safest anti-thrombotic treatment for peripheral arterial disease (Heart 2007; 93: 303-8).

What is the evidence?

  • Low-dosage aspirin is associated with a significant reduction in the risk for major cardiovascular events and all-cause mortality. It is also associated with a significant increase in the risk for major bleeding in patients with stable cardiovascular disease, meta-analysis findings show (Am J Med 2008; 121: 43-9). Despite the increased bleeding risk, the entirety of evidence still demonstrated the benefit of aspirin in this high-risk group of patients.
  • In a prospective observational study in two large UK general hospitals, aspirin was found to be the causal agent in 18 per cent of all admissions for adverse drug reactions (BMJ 2004; 329: 15-9).
  • Women derive different benefits to men from taking low-dosage aspirin for primary prevention of cardiovascular disease. The results of one study found that the number needed to treat to prevent one cardiovascular disease event over 6.4 years was 333 women and 270 men (JAMA 2006; 295: 306-13).
  • A US study has found that aspirin significantly lowered all-cause mortality in women with no history of cardiovascular disease (Arch Intern Med 2007; 167: 562-72).
  • A recent systematic review has shown that there is no evidence to use dosages greater than 75-81mg of aspirin a day for the prevention of cardiovascular disease, especially because higher dosages are associated with increased GI side-effects (JAMA 2007; 297: 2,018-24).
  • Taking long-term aspirin may have other benefits. One long-term trial showed that aspirin can reduce the incidence of colorectal cancer when taken at 300mg a day for at least five years (Lancet 2007; 396: 1,603-13).

Implications for practice

  • The absolute benefit of aspirin in people aged 55-9 years is around two first MIs avoided per 1,000 population each year (BMJ 2005; 330: 1,442-3).
  • However, the excess risks of GI bleeding with aspirin are 1-2/1,000 a year at age 60 and 7/1,000 a year at age 80.
  • Many patients with cardiovascular disease are 'resistant' or non-responsive to aspirin and are therefore more at risk of adverse cardiovascular events (BMJ 2008; 336: 195-8).

Dr Newson is a GP in the West Midlands and author of 'Hot Topics for MRCGP and General Practitioners', Pas Test 2006

Key points

  • Aspirin is increasingly being taken by healthy people.
  • Many people are at unnecessary risk of GI haemorrhage.
  • Aspirin still benefits those with high cardiovascular risk.
  • More research is needed before aspirin can be widely advocated.

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