To the Editor: We read with interest the article by Hung on aspirin for cardiovascular disease prevention,1 and would like to alert readers to the fact that, from the same studies Hung discussed, it is clear aspirin fails to prevent 80% of recurrent serious vascular events, and that one in eight high-risk patients will suffer from another “event” in the next 2 years while taking aspirin.2

Recent studies have triggered discussion about the concept of aspirin resistance and competitive binding issues as possible causes for the observed failure of aspirin, or indeed the increased risk of all-cause mortality when aspirin is used in combination with ibuprofen.3,4 Although it may still be premature to recommend routine testing for aspirin resistance, the possibility that testing might lead to improved strategies for reducing the risk of thrombotic complications means that it should be considered. Another point for consideration is whether primary prophylaxis with aspirin might induce aspirin resistance, thereby nullifying the effect of taking it in the first place.

We agree with Hung that the current main alternative to aspirin is clopidogrel, and that this agent could be used in cases in which there is any doubt about the efficacy of aspirin.

In reply: Janssen and Henshaw are correct to point out that aspirin fails to prevent 80% of recurrent serious vascular events among high-risk patients. However, to put this into perspective, simple treatment with aspirin produces about the same relative risk reduction as treatment with a statin or the angiotensin-converting enzyme inhibitor, ramipril, among patients at high risk of vascular events.1-3

Janssen and Henshaw raise the concept of aspirin resistance and the role of a screening test. However, aspirin resistance is a poorly defined term, and could mean the clinical inability of aspirin to protect individuals from arterial thrombotic events, or laboratory measures indicating the failure of aspirin to inhibit platelet activity. There is currently no specific, accurate, and reproducible measure of the antiplatelet effects of aspirin, nor are there methods that can reliably predict the clinical efficacy of aspirin.4 For now, with high-risk patients, doctors should:

• ensure that patients comply with aspirin therapy along with other proven preventive treatments;

• avoid regular concomitant use of non-steroidal anti-inflammatory drugs with aspirin because of the potential for competitive inhibition;5 and

• consider the addition of clopidogrel to therapy with aspirin, so as to block other pathways of platelet activation not blocked by aspirin, particularly in patients who experience thrombotic complications during aspirin therapy.1