About a month ago the FDA released a warning about an interaction between very commonly used medications:  aspirin and ibuprofen.

Many patients have been instructed to take low dose aspirin (81 mg daily) for heart attack or stroke prevention.  Aspirin prevents heart attacks and strokes by binding to an enzyme in platelets called cyclooxegenase (COX) and preventing its normal function.  COX is essential for platelet function, so aspirin prevents platelets from aggregating into small blood clots, which is an essential step in heart attacks and some strokes.  For the same reason, aspirin increases the risk of bleeding, since it inhibits normal blood clotting.

Patients on low dose aspirin sometimes need pain relief or anti-inflammatory medication, for example for a headache or a muscle sprain.  Doctors frequently prescribe ibuprofen (which is the medicine in Motrin and Advil), since it is a more effective pain medication than aspirin, and since additional aspirin will further increase bleeding risk.

The FDA alert cautions us that since ibuprofen also binds COX, though much more briefly than aspirin, taking the two together could prevent aspirin from binding, and potentially diminish aspirin’s effectiveness in heart attack and stroke prevention.  The alert suggests that in patients taking daily low dose aspirin who also need ibuprofen, the ibuprofen should be taken least 8 hours before or at least 30 minutes after the aspirin to minimize any interaction.

Another alternative is to use a pain reliever in an entirely different family, like acetaminophen (Tylenol).  This would eliminate any interaction with aspirin, but usually gives less pain relief than ibuprofen and has no anti-inflammatory properties.

I’m grateful to my colleague, Dr. Yaron Elad, for pointing me to this story.  It’s sobering that even with medications that have been around for many years and are used very commonly, we’re still learning new reasons to be cautious.