CORRESPONDENCE: LETTER TO THE EDITOR
Enteric Coating Is a Possible Cause of Aspirin Resistance
John R. Kapoor, MD, PhD*
* Division of Cardiology, Stanford University, 300 Pasteur Drive, Stanford, California 94305 (Email: jkapoor{at}stanford.edu).
The observation that aspirin does not inhibit platelet function as expected in some patients has been referred to as "aspirin resistance." The reported increased incidence of cardiovascular events in patients exhibiting aspirin resistance is indeed concerning (1,2) and highlights the importance of eliminating modifiable etiologies. In a recent issue of the Journal, Gasparyan et al. (3) discussed several of these causes, including poor compliance, nonsteroidal anti-inflammatory agents, and proton pump inhibitors. It is also important to take note of recent reports of incomplete suppression of platelet aggregation with enteric-coated aspirin (4,5). In a randomized, open-label, crossover study of healthy volunteers, incomplete thromboxane (TX) B2 inhibition was found to occur in 8% of the aspirin group and 54.3% of the enteric-coated aspirin group (p = 0.0004) (4). In another study of 131 stable cardiovascular patients treated with enteric-coated aspirin (75 mg/d), 44% of patients failed to attain optimal inhibition of serum TX, indicating suboptimal inhibition of platelet COX-1 activity, and those with an incomplete aspirin response were more likely to demonstrate platelet aggregation to arachidonic acid (21% vs. 3%; p = 0.004) (5). These data are of increasing importance when considering aspirin resistance because many patients now receive low-dose enteric-coated aspirin preparations for primary and secondary prevention of cardiovascular events.
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1. Eikelboom JW, Hirsh J, Weitz JI, Johnston M, Yi Q, Yusuf S. Aspirin-resistant thromboxane biosynthesis and the risk of myocardial infarction, stroke, or cardiovascular death in patients at high risk for cardiovascular events Circulation 2002;105:1650-1655.[Abstract/Free Full Text]2. Gum PA, Kottke-Marchant K, Welsh PA, White J, Topol EJ. A prospective, blinded determination of the natural history of aspirin resistance among stable patients with cardiovascular disease J Am Coll Cardiol 2003;41:961-965.[Abstract/Free Full Text] 3. Gasparyan AY, Watson T, Lip GY. The role of aspirin in cardiovascular prevention: implications of aspirin resistance J Am Coll Cardiol 2008;51:1829-1843.[Abstract/Free Full Text] 4. Cox D, Maree AO, Dooley M, Conroy R, Byrne MF, Fitzgerald DJ. Effect of enteric coating on antiplatelet activity of low-dose aspirin in healthy volunteers Stroke 2006;37:2153-2158.[Abstract/Free Full Text] 5. Maree AO, Curtin RJ, Dooley M, et al. Platelet response to low-dose enteric-coated aspirin in patients with stable cardiovascular disease J Am Coll Cardiol 2005;46:1258-1263.[Abstract/Free Full Text]
Related Article
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- Armen Yuri Gasparyan and Gregory Y.H. Lip
J. Am. Coll. Cardiol. 2008 52: 1277.
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