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FDA Updates Coumadin Label to Warn of Genetic Risks

Aug 21, 2007 | Parker Waichman LLP, LLP

The Food & Drug Administration (FDA) has approved a label update for a popular blood thinner.   The new label for Coumadin will warn doctors that patients with specific genetic make-ups might not respond well to the drug.  The FDA says that about 30 percent of the patients who take Coumadin (known generically as warfarin) could carry genes that affect how they metabolize the blood thinner.

About 2 million people in the United States take Coumadin, although it can be a difficult drug to administer.  The proper dosage of Coumadin is based on several factors, including age, diet and other medications a patient may be using.  If the dose is too high, patients can suffer severe internal bleeding.  But if it is too low, they run the risk of developing blood clots.  Usually, when a patient starts taking Coumadin, their blood is checked over several days to determine the correct dosing.  Then, patients are tested monthly to see if the drug is working.   According to the FDA,  problems with Coumadin are the second most common drug side effects to result in emergency room visits.   

About a third of the people taking Coumadin seem to metabolize the drug differently than most patients.   According to the FDA, two gene variants,  CYP2C9 and VKORC1, were present in many of the patients who had this problem.   As a result, some patients with the variants might need lower doses of the blood-thinning medication.  The FDA said that the label changes were based on recent studies into these gene variants.  

The new labeling is part of the FDA’s “personalized medicine” initiative that makes use of pharmacogenomics.  Pharmacogenomics is the science that predicts a person’s response to a drug based on their genetic make up.  According to the FDA, differences in gene sequences between individuals can affect how drugs are processed.  Last week as part of the initiative, the FDA warned nursing mothers to exercise caution when using drugs with codeine.  Another gene variant can cause some mothers to metabolize codeine more quickly, causing more of the drug to be present in their breast milk.  When this happens, their babies are at risk of overdose.

The FDA stopped short of mandating genetic testing of Coumadin patients.   Such tests can cost as much as $500, and are not available in all parts of the country.   Also, the FDA said that the genetic testing available at this time may not be an accurate predictor of a patient’s reaction to Coumadin.  The FDA is currently funding projects that are aimed at developing genetically based guidelines for Coumadin dosage.   


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