Heart Health Treatments

Undermining the Effectiveness of Aspirin Therapy

Who is a good candidate for daily aspirin therapy?
Someone who is at high risk for cardiovascular disease is generally a good candidate. Risk factors for heart attack include high blood pressure, cholesterol and family history of heart attack or diabetes.

Of course, people who do not tolerate aspirin, who have allergic reactions or have had bleeding events such as gastrointestinal bleeding, should not take aspirin. Bleeding events can occur with aspirin therapy because one of the ways aspirin works is by inhibiting the aggregation of platelets blood cells that assist in clotting.

How does aspirin reduce risk?
Aspirin interacts with an enzyme called cyclooxygenase-1, the so-called COX-1 enzyme. By doing so, it irreversibly inhibits the aggregation of platelets. An aggregation of the platelets can cause clotting in the arteries, which can lead to a heart attack or an ischemic stroke. So if you take aspirin and this aggregation is inhibited, you're less likely to have such events.

How do the other NSAIDs work?
There are several different so-called NSAIDs, including aspirin and ibuprofen. These drugs are also working on the COX enzyme. In the COX family, there are several forms of this enzyme and, with aspirin and other NSAIDs, COX-1 and 2 play a role. COX-2 is involved in the pain pathway. There is a newer generation of NSAIDs that only interact with COX-2, and not with COX-1. Virtually none of our participants took COX-2 inhibitors, however, because the study took place before these drugs were on the market. [Since the publication of this article, the COX-2 inhibitor Vioxx has been taken off of the market because of links to increased heart attack and stroke risk, and the safety of other COX-2 inhibitors has been called into question.]

Why do some NSAIDs inhibit aspirin?
Both aspirin and other non-aspirin NSAIDs can work on the COX-1 enzyme. But, the enzyme can probably be blocked only by either aspirin OR another NSAID. Unlike aspirin, however, other NSAIDs impair platelet function for just a limited time, and the platelets regain function after these NSAIDs leave the body. Thus, if both medications are taken together, other NSAIDs may interfere with aspirin's effect on COX-1.

What did your study find?
First, the overall study found that aspirin was highly effective to prevent first heart attack, with a 44 percent risk reduction. The most stable result of our study is that occasional users of NSAID, which are probably most users of NSAIDs, are not affected by an interaction of aspirin and other NSAIDs. Our studies suggest that those who take other NSAIDs regularly do not have the beneficial effect of aspirin, which does not mean that there is an increased risk of heart attack compared to taking nothing, but just that aspirin is not as efficient if you take the other NSAIDs regularly.

What are the options for people who take daily aspirin and have chronic pain?
That is very difficult to answer at this point. But one study suggested that if you take your aspirin somewhat before your NSAID, the interaction might not occur. When you take your aspirin before, the aspirin has time to work on the COX-1 enzyme. Then when you take your other NSAID, it won't interact with aspirin because the COX-1 is already being blocked by aspirin.

So if you take the aspirin and then somewhat later, let's say around two hours or so take the NSAID for pain, you might avoid the problem. We need more information, but to the best of my knowledge, that might be a solution.

Is it known if certain NSAIDs inhibit aspirin less than or more than others?
In our study, we had no information about specific NSAIDs. In the first two studies that came out, this effect was only shown for ibuprofen, but not for other NSAIDs.

Should someone experiencing pain stop taking aspirin therapy temporarily?
No, that's not a good idea. Even if, in theory, that effect might be gone if you're taking an NSAID, you still want to continue to take the aspirin.

If you have to take aspirin and another NSAID regularly, I think the best recommendation is to talk to the treating physician about this issue. See if you should take your aspirin prior to the NSAID.

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