Thursday, December 17, 2009

Pain Relieving Coxibs Counter Aspirin’s Benefits

Millions of persons are prescribed COX-2 inhibitors, or coxibs, like Celebrex® for arthritis and other pain. However, coxibs may undermine the anti-clotting benefits of low-dose aspirin taken daily to reduce risk of heart attack or stroke in these patients, according to new research.

In laboratory studies, University of Michigan researchers found that coxibs interfere with aspirin’s ability to discourage blood clot formation, if the aspirin is taken in low doses such as the recommended 81 mg/day. “The greatest risk,” according to William L. Smith, PhD, the study’s senior author, “is having people take Celebrex who are taking aspirin for cardiovascular problems that are known to be mitigated by aspirin, including patients with unstable angina or those at risk for a second heart attack.” Celebrex brand of celecoxib is the only coxib still on the market in the United States, and previous studies of healthy subjects found no ill effect on blood clotting when Celebrex was combined with aspirin at higher doses, specifically a daily “regular” aspirin tablet (324 mg). So, Smith notes, it may be that spreading out the time between taking low-dose aspirin and Celebrex or a higher aspirin dose will allow aspirin to be effective. Of course, at higher doses aspirin’s undesirable effects on the gastrointestinal tract must to be taken into account.

Caveats: This study was in laboratory animals and the detrimental effects need to be replicated in humans. If the problems are evident in people, it will be important to determine if a balance in dose and/or dose regimens can be found so that aspirin and Celebrex can both be effective. At present, more than half of older patients prescribed COX-2 inhibitors long-term are also taking low-dose aspirin to protect against thrombosis, and practitioners should be aware of the possibility that the aspirin might not be delivering the expected and desired anticoagulant effect.

Reference: Rimona G, Sidhua RS. Lauverc A, et al. Coxibs interfere with the action of aspirin by binding tightly to one monomer of cyclooxygenase-1. Proceedings of the National Academy of Sciences (PNAS). 2009 (Dec 1, advance online publication) [abstract here].