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"Ann Arbor, MI - New laboratory research suggests that the COX-2 inhibitor celecoxib (Celebrex, Pfizer), might impede the action of "baby" aspirin [1]. Dr Gilad Rimon (University of Michigan, Ann Arbor) and colleagues found evidence that this was the case in a dog model and say that "it will be important to determine" whether the same is true in humans. The report was published online December 1, 2009 in the Proceedings of the National Academy of Medicine. Celecoxib is the only COX-2 inhibitor to have remained on the market in the US, and doctors who recommend this painkiller often coprescribe a daily low dose of 81 mg of aspirin (known as a "baby" dose) to counteract any possible prothrombotic effects of the coxib, while minimizing potential gastrointestinal toxicity of the aspirin. Senior author of the new work, Dr William L Smith (University of Michigan, Ann Arbor), explained to heartwire that previous studies in humans have shown that celecoxib does not interfere with the effect of a standard dose of aspirin (325 mg), but any potential interaction of celecoxib with the lower dose has not been examined. Stagger dosing to avoid any potential problems First, Smith explained that he and his colleagues looked in vitro at celecoxib and found that it binds to one of two available sites on the COX-1 enzyme. "This surprised us," he commented. "It appears to interfere with the ability of some other drugs to affect COX-1, most notably aspirin." Second, in beagles, they administered the dog-equivalent of a baby dose of aspirin in humans and then gave some of the animals the equivalent of 100 mg of celecoxib twice daily in addition. "Celecoxib plus aspirin interfered with the normal effect of low-dose aspirin on platelets," he notes. Smith says this observation obviously requires confirmation in humans, but in the meantime he suggests "getting around the problem" by patients taking the low-dose aspirin at least 15 to 30 minutes before the celecoxib is taken, "because