The Food and Drug Administration (FDA) recently announced a "Black Box" warning for the drug Plavix (clopidogrel), a type of blood-thinner often given to patients who have had a heart attack or received stents. While most doctors agree that this medication is important for patients who are at risk for blood clots that can block an artery, possibly causing a heart attack or a stroke, the FDA is concerned about a small percentage of patients who may not receive the full benefits of the medicine.
Here's how Plavix is supposed to work: After a patient swallows a Plavix tablet, the body must "metabolize" the drug before it becomes active and starts to work, in this case thinning the blood and preventing blood clots.
A small body of research has suggested that about 3% of U.S. patients have a genetic variation that prevents their bodies from metabolizing the drug Plavix efficiently. As a result, they do not get the full anti-clotting effects of the drug. These patients, known as "poor metabolizers," have recently been shown to have a higher chance of having a heart attack, despite being on the drug.
Future studies should address which patients should be tested for this genetic variability and how doctors should modify treatment strategies when a "poor metabolizer" is identified. In the meantime, it is most important that heart patients do not stop taking their Plavix, aspirin, or any other prescribed medicine without asking their cardiologist, as this may lead to a heart attack. In fact, not taking medications as prescribed is much more likely to cause "Plavix failure" than being a poor metabolizer.