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Determination of who may derive most benefit from aspirin in primary prevention: subgroup results from a randomised controlled trial

BMJ 2000; 321 doi: https://doi.org/10.1136/bmj.321.7252.13 (Published 01 July 2000) Cite this as: BMJ 2000;321:13

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Benefit v. Risk of Aspirin in primary prevention.

Editor,

The 1999 British Hypertension Society Guidelines recommended Aspirin
75mg to reduce the risk of cardiovascular events in patients of age 50 and
over with a 10 year risk of cardiovascular disease of more than 15% and
blood pressure controlled to 150/90 or below (1). The principal support
for this recommendation comes from the HOT study (2). Meade and Brennan
(3) have questioned this recommendation on the basis that, in a subgroup
analysis of the MRC Thrombosis Prevention Trial (4), the beneficial effect
of aspirin was limited to those patients with systolic blood pressure less
than 145mmHg.

Many General Practitioners will be considering using Aspirin for
primary prevention in line with the BHS guidelines. A recent audit in our
practice indicated that whilst 75% of patients eligible to receive aspirin
for secondary prevention of cardiovascular disease were receiving it, only
23% of hypertensives above age 50 years were receiving it. Steps were
taken to address this gap, revising practice protocols and producing a
list of eligible patients.

The debate raised by Meade and Brennan prompted us to examine the HOT
study in detail, with particular reference to the risk:benefit ratio for
aspirin in this context. In the HOT study the principal benefit of aspirin
was a 15% reduction in major cardiovascular events. However the absolute
reduction in risk was only 1.6 per 1000 patients at risk over 3.8 years,
an NNT of 625 to prevent one major event over 4 years. The principal risk
of low dose aspirin therapy is of upper gastrointestinal bleeding.
Although the risk of fatal bleeding was very low (15 events in 18,790
patients) the absolute risk of a major non-fatal bleed was 6.5 per 1000,
representing an number need to harm of 154.

General practitioners and their patients may feel less enthusiastic
about the role of aspirin in primary prevention when confronted with four
patients with a major aspirin-related bleed for every cardiovascular event
avoided.

Dr Brendan Delaney, Senior Lecturer in General Practice, Department
of Primary Care and General Practice, The University of Birmingham,
Edgbaston, Birmingham, B15 2TT

Dr Sheena Kulshrestha, GP Registrar, Laurie Pike Health Centre, 95
Birchfield Rd, Handsworth, Birmingham B19 1LH.

References

1. Ramsay LE, Williams B, Johnston GD, MacGregor GA, Poston L, et al.
British Hypertension Society guidelines for hypertension management 1999:
summary. BMJ 1999; 319: 630-635.

2. Hansson L, Zanchetti A, Carruthers SG, Dahlof B, Elmfeldt D,
Julius S, et al. Effects of intensive blood-pressure lowering and low-dose
aspirin in patients with hypertension: principal results of the
hypertension optimal treatment (HOT) randomised trial. Lancet 1998; 351:
1755-1762.

3. T W Meade and P J Brennan. Determination of who may derive most
benefit from aspirin in primary prevention: subgroup results from a
randomised controlled trial. BMJ 2000; 321: 13-17.

4. General Practice Research Framework Thrombosis Prevention Trial.
Randomised trial of low-intensity oral anticoagulation with warfarin and
low-dose aspirin in the primary prevention of ischaemic heart disease in
men at increased risk. A report from the MRC's general practice research
framework. Lancet 1998; 351: 233-241.

Competing interests: No competing interests

19 July 2000
Brendan Delaney
Senior Lecturer in General Practice
The University of Birmingham, UK