Celecoxib Could Impede Effects of Low-Dose Aspirin

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 200 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 the effect of aspirin on platelets is rather quick." If the two drugs are taken at the same time, "you can almost guarantee the aspirin won't be working," he says.

If the effects of celecoxib on low-dose aspirin are replicated in humans, "the greatest risk will be having people take celecoxib who are taking aspirin for cardiovascular problems that are known to be mitigated by aspirin, such as those with unstable angina or after a first heart attack," he notes. "These patients would definitely have to be careful about taking celecoxib; it's a real issue."

Interestingly, in dogs, celecoxib does not seem to blunt the effects of a standard dose of aspirin, similar to what is seen in humans, Smith notes