Interactions May Have Deadly Results

Ask any sixth grader what 1+1 equals and you will be told the answer is 2. Ask a pharmacist, though, and you might get a different answer.

In the Alice-in-Wonderland world of pharmaceuticals, sometimes 1+1 equals 0 or even 3. That's because certain drugs may cancel out the benefits of other medicine or exaggerate their effects and cause toxicity.

Plavix offers a recent example. When people develop serious blockage in a coronary artery surgeons frequently insert a balloon catheter to widen the passageway. To keep it from closing later, they almost always insert a stent.

Although these little metal mesh tubes help keep heart arteries open, they too may sometimes get clogged. That is why there has been great interest in a newer generation of devices called drug-eluting stents. These tiny tubes are coated with an immune-suppressing medication that keeps tissue from growing around the metal.

While that seems like an improvement, it creates problems of its own. Bare metal is more likely to trigger a blood clot. And that's where Plavix comes in.

This medicine prevents life-threatening blood clots from forming in coronary arteries. There's not much room for error. Too much drug can lead to bleeding; too little can allow deadly clots to form.

One fairly common side effect of Plavix is digestive distress. Not surprisingly, doctors frequently prescribe the most popular heartburn medicines on the market. That includes Nexium (the "purple pill") and similar proton pump inhibitors (PPIs) such as Prevacid, Prilosec and Protonix.

There is a huge problem, however. When PPIs are combined with Plavix we may enter the zone where 1+1 don't always equal 2. More than 16,600 stent recipients were studied by Indiana University School of Medicine and Medco Health Solutions. The data show that patients given a PPI along with Plavix are 50 percent more likely to suffer a heart attack or a stroke than those taking Plavix alone.

This study is consistent with findings reported from the VA earlier this year (Journal of the American Medical Association, March 4, 2009). That study also found that people taking both Plavix and a PPI were more likely to die or suffer cardiovascular complications.

The scientists suspect that the heartburn drugs interfere with the effectiveness of Plavix. This is not the only drug combination that may result in reduced effectiveness.

People who take thyroid hormone (levothyroxine, Levoxyl, Synthroid) are warned not to take calcium supplements at the same time. Calcium can interfere with absorption of the hormone. Some antibiotics may also be less effective when taken with calcium in antacids, supplements or foods.

Other drug interactions may result in unexpected toxicity. This is especially true for medicines like digoxin (Lanoxin) or warfarin (Coumadin), which interact with dozens of other drugs. To learn more about the crazy and confusing mine field of drug interactions, readers may be interested in our book, Dangerous Drug Interactions. It is available in libraries, bookstores and online at www.peoplespharmacy.com.

Thousands of drug interactions pose potential hazards. When physicians and pharmacists are too busy to look up potential conflicts, patients will need to watch out for themselves