Medical Laboratory Observer - Hitting the target with antithrombotic therapy
Every day, millions of women take a blood thinner called warfarin (Coumadin) to reduce their risk of stroke. It’s commonly prescribed for people with atrial fibrillation (AF), an abnormal heart rhythm that causes the upper chambers of the heart (atria) to quiver ineffectively rather than contract normally, allowing blood to pool and potentially form clots. Although warfarin can cut the risk of stroke by more than 60 percent, it can also increase the chance of hemorrhage. Determining the initial dose can be difficult, and the drug must be managed with monthly blood tests to make sure a patient is taking just the right amount; too much can cause bleeding. Diet and medications (including some antiarrhythmic drugs) also affect warfarin.
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Scientists have discovered two genes related to warfarin. Pilot studies are underway to see if genetic testing can help determine the best dose of warfarin more quickly and lessen side effects.
The effect of genes
One gene, known as CYP2C9, produces a liver enzyme that helps the body metabolize warfarin and other medications, explains Bindi Shah, MD, an assistant professor of medicine at the Weill Medical College of Cornell University. “If a patient has a variant in that gene, the drug may be metabolized more slowly, so that patient may need a smaller dose,” says Dr. Shah. The second gene, VKORC1, is a vitamin K-related gene that produces the clotting protein blocked by warfarin. People with that gene may produce less of the protein and also need smaller doses. The U.S. Food and Drug Administration is changing the labeling on Coumadin and generic warfarin to warn doctors that some patients’ genes may require lower doses.
AF patients with no additional risk factors for stroke can take 81-325 mg of aspirin daily to prevent clots. Patients over age 60 can take either aspirin or warfarin. Those over age 75, or who have high blood pressure, diabetes, or who have had a previous stroke, must take warfarin. It’s not clear if genetic testing may eventually play a role in matching patients with the best therapy, says Dr. Shah.
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COPYRIGHT 2008 Gale, Cengage Learning
