Combining aspirin with the pain medication valdecoxib (Bextra®, Pfizer) may increase the risk of blood clots that can trigger a heart attack or stroke. In December, the FDA warned that valde-coxib should not be used in candidates for heart bypass surgery.
Low-dose aspirin can slow the development of atherosclerosis in mice, but it seems ineffective once the disease is established. Adding a COX-2 inhibitor does not enhance the beneficial effects of aspirin; instead, the combination of valde-coxib and aspirin produces potentially dangerous changes in the makeup of the plaque within the arteries. The added COX-2 inhibitor causes changes that—if they occurred in humans—would result in a loss of stability of the plaque, making it more likely to rupture and activate clotting, causing heart attack or stroke.
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Researchers say aspirin prevents atherosclerosis by blocking COX-1. Adding a COX-2 inhibitor may cause the beneficial effects of aspirin to be lost. This could increase the chance of developing dangerous blood clots.
Researchers caution that these results should not be taken out of context; the patients were at high risk for heart problems because they were undergoing heart bypass surgery. However, they say the findings represent a class effect of the COX-2 inhibitors.