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| |  Genetic Information Can Improve Administration of Warfarin CHAPEL HILL, NC -- February 19, 2009 -- A study published in the February 19 issue of the New England Journal of Medicine suggests that using a patient's genetic information can make it easier to get the initial dose of warfarin right. Researchers from the International Warfarin Pharmacogenetics Consortium have shown that taking 2 genes into account can result in a warfarin dose that is closer to being right the first time. "Our analysis shows that the pharmacogenetic test is better at identifying patients who lie at either the high end or the low end of the warfarin-dose spectrum," said coauthor Michael Wagner, PhD, Eshelman School of Pharmacy, University of North Carolina, Chapel Hill, North Carolina. "That's important because nearly half of the people taking warfarin fall into those extreme ranges, putting them at the greatest risk for excessive bleeding or clotting." Variations in cytochrome P450, subfamily 2C, polypeptide 9 (CYP2C9), and vitamin K epoxide reductase complex 1 (VKORC1) affect how much warfarin a person needs to achieve the desired effect. In 2007 the US Food and Drug Administration (FDA) added this genetic information to the warfarin label but did not specify how the information could be used. To begin developing guidelines, consortium members pooled clinical and genetic data from 5,052 patients taking warfarin from 21 centres around the world. Because these patients were already on warfarin, the researchers knew the appropriate dose for each person. They then created 3 different dosing strategies designed to recommend an initial dose for each patient. The first was a fixed dose of 5 mg; the second method factored in clinical data such as age, weight, and medical condition; and the third combined the clinical information with the patient's genetic profile. The 3 strategies were compared to see which one best predicted an initial dose that was within 20% of the dose a patient was taking, a threshold that the researchers considered to be a meaningful difference. For the 46% of patients requiring <3 or >7 mg of warfarin each day, using genetic information resulted in a more accurate dose. For patients needing the smaller dose, the pharmacogenetic method made a correct prediction nearly 50% of the time, compared with the clinical information alone, which was accurate only one-third of the time. For those who required a larger dose, the pharmacogenetic guideline predicted the correct dose nearly 25% of the time, compared with the clinical method's 7% success rate.
SOURCE: University of North Carolina at Chapel Hill
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