Change Ordered to Warfarin Drug Label
Warfarin Label Says Dosage May Depend on Genetic Test
Aug. 1, 2007 - In a new trend, labels on the clot-fighting drug warfarin
will now warn that people with certain gene variations may need lower doses
of the drug.
It's the first time that the FDA has asked doctors to consider a patient's
genetic makeup when prescribing a widely used drug, says Larry Lesko, PhD,
director of clinical pharmacology at the FDA.
"Today is a significant event for those who see the day when medicine is
tailored to the genetic makeup of each one of its users," Lesko said at a
"We are continuing to engage in various projects that will further
evaluate the relationship between genetic variability and treatment outcomes in
patients," FDA Deputy Commissioner and Chief Medical Officer Janet
Woodcock, MD, said at the news conference.
The change in the label for warfarin (originally sold under the brand name
Coumadin) does not require
that patients get genetic tests. But the new label suggests that genetic
testing can help doctors find the correct dosage of the drug.
Each year, about 2 million Americans start taking warfarin to prevent blood
clots, heart attacks, and strokes. It is notoriously difficult to find the
right warfarin dosage for an individual patient. Factors such as age, diet, use
of other medications, and use of vitamins and supplements affect the
Because of this, warfarin is the second most common drug (after insulin)
that sends patients to the emergency room.
Researchers have noticed that about a third of patients who start warfarin
need much lower doses than expected. This difference appears to be due to
variations in two genes. One of the genes, VKORC1, affects a patient's
sensitivity to warfarin. The other gene, CYP2C9, affects how quickly a person
clears warfarin from the body.
The new warfarin label suggests that doctors starting a patient on warfarin
might want to have that patient tested for variations in these genes. Most
major laboratories already offer the test. Lesko says the cost of testing
ranges from $125 to $500; a patient would need to be tested only once.
Patients already taking warfarin probably will not need genetic testing if
they already have found the warfarin dosage that works best for them.