Posted by: bescothealthcare | August 4, 2011

Consequences of Non-adherence with Aspirin*

Discontinuation of low dose Aspirin* and risk of myocardial infarction: case-control study in UK primary care

Garcia et al BMJ 2011; 343

There is amble evidence to support the use of low dose Aspirin* (75-150mg) as a protective agent in most types of patients who have had a previous cardiovascular event.  However, discontinuation rates of up to 50% have been reported amongst patients taking this medication for a number of years. Discontinuation may well be for a number of reasons; a treatment change, safety concerns, a switch from Rx to OTC Aspirin*, and non-adherence. Non-adherence is a “silent killer” in that the treating physician is likely unaware of the issue and patients who discontinue are exposed to a three-fold increased risk of adverse cardiovascular events, compared to those continuing to take Aspirin*.  This increased risk is seen as soon as four weeks after discontinuation.

This study confirms this picture by extending the data collection from secondary care centres to primary care. The Health Improvement Network (THIN) database in the UK looked at 39,513 individuals aged 50-84 with previous cardiovascular events in 2000-7. Follow-up was for an average of 3.2 years.

Compared to current aspirin* users, people who had stopped taking aspirin for any reason had a significantly increased risk (odds ratio 1.43).  This ratio was higher for those who discontinued for non-adherence (odds ratio 1.54).  Of the 1,222 people with cardiovascular events 75 (6.1%) were in non-adherent people vs 242 out of 5,000 controls (4.8%).

One key conclusion from this study is that, for whatever reason, people discontinue low dose Aspirin* despite there being clear evidence that it is beneficial. Reducing this number could therefore have a major impact on the benefit obtained with low dose aspirin in the general population.  Non-adherence is a major problem typically dealt with by patient questioning which is clearly inadequate. ASA Effect is a simple random urine based assay that measures the urinary metabolite of thromboxane A. The use of ASA Effect to evaluate the clinical effectiveness of aspirin could be a simple, low cost approach to objectively evaluate the level of adherence.

Note* – In Canada, Aspirin is a trademark of Bayer AG, used under license.

The full article can be found at http://www.bmj.com/content/343/bmj.d4094.full?sid=99ce7930-63e0-40dd-b550-2c6934d9607f

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