Physicians and Healthcare Providers

Warfarin’s efficacy as an anti-clotting medication is well established. But dosing remains a challenge due to serious side effects including life-threatening bleeding. The optimal maintenance dose of warfarin for each patient is difficult to predict at the beginning of treatment, and it can take several weeks of frequent monitoring before a stable maintenance dose is established. While changes in the prothrombin time (PT) may reflect changes in warfarin dose, they may also be due to changes in diet and concomitant medications.

PGxPredict™:WARFARIN test helps solve this problem, reducing uncertainly by predicting a patient’s response to warfarin before the drug is prescribed. It tests for genetic markers that are not affected by diet or concomitant medications.

In August 2007, the FDA approved updated prescribing information for warfarin to include information on the use of genetic testing (CYP2C9 and VKORC1) to optimize dose for the management of blood clots and bleeding.¹ This action follows the Clinical Pharmacology Subcommittee of the FDA’s Advisory Committee for Pharmaceutical Sciences having strongly advocated for the inclusion of genotype information in the prescribing of warfarin in November 2005. At that time, they agreed that:

• “Sufficient mechanistic and clinical evidence exists to use lower doses of warfarin for patients with genetic variations in CYP2C9 that lead to reduced activity and genotyping patients in the induction phase of warfarin therapy would reduce adverse events and improve achievement of stable INR in patients with genetic variations in CYP2C9.”
• “Sufficient mechanistic and clinical evidence exists to use lower doses of warfarin for patients with genetic variations in VKORC1 that lead to reduced VKORC1 activity and genotyping patients in the induction phase of warfarin therapy would reduce adverse events and improve achievement of stable INR in patients with genetic variations in VKORC1.”²

PGxPredict:WARFARIN test is a simple test that may bring about safer dosing, better patient outcomes, and peace of mind for physicians.

In early 2008 the American Medical Association and several partners issued a personalized health care report on warfarin and genetic testing. The report notes that twenty-one percent of patients who receive anticoagulation therapy experience either major or minor bleeding events and that knowing a patient’s genotype may aid in initial warfarin dosing. The report can be viewed at the AMA website and printed versions can be ordered.   

References

¹ Food and Drug Administration’s announcement of label change, August 2007 http://www.fda.gov/bbs/topics/NEWS/2007/NEW01684.html

² Food and Drug Administration’s (FDA) Advisory Committee for Pharmaceutical Sciences http://www.fda.gov/ohrms/dockets/ac/05/minutes/2005-4194M1.pdf

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