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The waiting game

When is aspirin worth risking in raised BP?

QWhat is the risk of taking 75mg of aspirin in someone over 50 with controlled hypertension?

AAspirin reduces the relative risk of cardiovascular events by about 30 per cent, but the degree to which it lowers the absolute risk will be dependent on the risks to the individual patients.

Aspirin also causes harm (largely due to gastrointestinal haemorrhage) in about one in seven cases. Assessing individual risk is often a matter of clinical judgment.

Nevertheless, if a patient has no particular reason to be at increased risk of gastrointestinal side-effects, it is possible to calculate when the absolute benefits of aspirin are likely to outweigh the absolute risks. So for primary prevention, if the predicted cardiovascular event rate is greater than 0.8 per cent per year aspirin will probably do more good than harm.

In contrast, if the predicted cardiovascular event rate is lower than 0.5 per cent per year the unwanted effects of aspirin outweigh any benefit.

A recent analysis suggested that taking all bleeds into account and considering the numbers of patients needing to be treated, patients with a coronary heart disease event rate of 1.5 per cent per year or higher should be treated with aspirin (provided there is no other contraindication) and that individuals with a risk lower than 1 per cent per year should not. For the patient described, the answer depends on a calculation of their absolute cardiovascular risk.

If they also take an NSAID then it is possible (but not proven) that the beneficial effects of aspirin may be lost, while the unwanted effects will be increased. Equivalent data for clopidogrel are not yet available. It is reasonable to assume a lower GI bleed rate and probably a similar rate of effectiveness but it costs 100 times more.

Professor Patrick Vallance is director of the Centre for Clinical Pharmacology, Royal Free and University College Medical School, London

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