New warfarin labelling recommends genetic testing to guide initial warfarin dosing

The U.S. FDA is updating the label for warfarin to include information reminding physicians that people with variations in two genes, CYP2C9 or VKORC1, may require a lower initial dose of the drug. “The FDA labeling change for warfarin is the next step in the pathway toward incorporating genetics into the care of patients who need anticoagulation. The FDA has said that physicians should be aware of the role of genetics in warfarin dosing, but now the hard part is doing the necessary groundwork to determine how best to use genetic testing to improve care,” said Marc Williams, Board Member and a co-chair of the expert group on Pharmacogenetic Testing of CYP2C9 and VKORC1 Alleles for Warfarin Use. The new labeling does not dictate how physicians should change the dosage as no clinical trials have yet shown that using a genetic test to determine initial warfarin dosing actually has an impact on the safety or efficacy of the drug. “Although genetic testing can currently identify who has these genetic variants, more studies are needed to explore the precise starting dose for these patients,” said Larry Lesko, Ph.D., director of the FDA's Office of Clinical Pharmacology. “FDA has been working with other government agencies and organizations to develop such studies under the auspices of our three-year-old Critical Path Initiative, which addresses the challenges of moving promising medical products from discovery to patient use.” Reference...