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    Medication Labeling Alert August 21, 2007
The following was posted on FDA Med Watch alert website dated August 16, 2007: "FDA approved updated labeling to include pharmacogenomics information to the CLINICAL PHARMACOLOGY, PRECAUTIONS, and DOSAGE AND ADMINISTRATION sections of the prescribing information for the widely used blood-thinning drug, Coumadin. This new information explains that people's genetic makeup may influence how they respond to the drug. Specifically, people with variations in two genes may need lower warfarin doses than people without these genetic variations. The two genes are called CYP2C9 and VKORC1. The CYP2C9 gene is involved in the breakdown (metabolism) of warfarin and the VKORC1 gene helps regulate the ability of warfarin to prevent blood from clotting. The dosage and administration of warfarin must be individualized for each patient according to the particular patient's prothrombin time (PT) / International Normalized Ratio (INR) response to the drug. The specific dose recommendations are described in the warfarin product labeling, along with the new information regarding the impact of genetic information upon the initial dose and the response to warfarin. Ongoing warfarin therapy should be guided by continued INR monitoring." An excerpt from the FDA’s "Questions and Answers on New Labeling for Warfarin" is provided below: How will this new warfarin label information benefit patients? This information will benefit patients because it will describe why patients with a variation in the CYP2C9 and/or VKORC1 genes may need a lower warfarin dose than patients with the usual forms of these genes. For patients with these genetic variations, the new label information may help physicians prescribe the correct warfarin dose and also encourage them to give increased attention to how these patients respond to warfarin. How might healthcare professionals use this information in their practice? Healthcare professionals might incorporate the genetic information on CYP2C9 and VKORC1, along with various clinical considerations and patient characteristics (e.g., age, body weight) to better estimate the initial warfarin doses for patients. Warfarin is often administered daily and the response to the drug is mainly measured by a laboratory test result called the INR. The INR measures, in part, the blood's ability to clot and the INR should be performed regularly in all patients receiving warfarin. Genetic information does not replace regular INR testing. Will healthcare professionals be required to test patients for these genetic variations prior to prescribing warfarin? No, healthcare professionals are not required to conduct CYP2C9 and VKORC1 testing before initiating warfarin therapy, nor should genetic testing delay the start of warfarin therapy. What did clinical studies show to support the addition of genetic information to the warfarin label? Clinical studies have shown that patients with CYP2C9 and VKORC1 genetic variations require lower warfarin initial and maintenance dose to stay within the target INR. Future clinical studies are expected to identify which initial warfarin doses are most appropriate for people with different CYP2C9 and VKORC1 gene variants. Many these studies are described at the internet address of: www.clinicaltrials.gov (using the "warfarin" search term). |
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