By themselves, low-dose aspirin and the painkiller Vioxx are usually safe for the stomach, but together they can spell trouble, a new study indicates.

The findings may be relevant to many people who take aspirin to prevent heart problems as well as a COX-2 inhibitor drug like Vioxx for arthritis.

The study, in the medical journal Gastroenterology, found that when patients who routinely take low-dose aspirin are also treated with Vioxx, the incidence of stomach ulcers increases to a rate comparable to that seen with ibuprofen, a traditional nonsteroidal anti-inflammatory drug.

Compared to nonsteroidal anti-inflammatory drugs, COX-2 selective inhibitors have a significantly lower risk of gastrointestinal side effects, according to a multicenter team led by Dr. Loren Laine of the University of Southern California School of Medicine in Los Angeles.

They point out that aspirin, even at low doses, carries some risk for GI complications such as bleeding, but until now there have been no trials looking at the interaction of low-dose aspirin with COX-2 inhibitors.

In the researchers’ current study, 1,615 patients with osteoarthritis who were at least 50 years old were randomly assigned to take either inactive placebo pills, enteric-coated aspirin at a dose of 81 milligrams per day, 800 milligrams of ibuprofen 3 times daily, or a combination of the low-dose enteric-coated aspirin and Vioxx (rofecoxib), 25 mg daily.

After 12 weeks of treatment, stomach ulcers occurred in 5.8 percent of those in the placebo group, 7.3 percent of the aspirin-alone group, 17.1 percent in the ibuprofen group, and 16.1 percent in the combination aspirin/COX-2 group.

In other words, the investigators point out, low-dose aspirin alone did not significantly increase the risk of ulcers. The addition of Vioxx, however, brought the incidence of ulcers up “to a rate not significantly less than a nonsteroidal anti-inflammatory drug (NSAID) alone.”

It will require another study, the team adds, to determine “the relative impact of COX-2 selective inhibitors and nonselective NSAIDs on gastrointestinal mucosal injury in low-dose aspirin users.”

SOURCE: Gastroenterology, August 2004.