Warfarin Dosing Accuracy and Genomic Medicine: A Helix Health CliniCast

Reading time: 4 – 6 minutes

Warfarin, also known under the brand names of Coumadin, Jantoven, Marevan and Waran, is an oral anticoagulant used worldwide for the treatment and prevention of thromboembolic disease. However, warfarin therapy can be difficult to manage because there is a wide variability in patient response and the drug has a narrow therapeutic index. Taking too small a dose can lead to a blood clot while too much can cause life-threatening bleeding.

Single nucleotide polymorphisms (SNPs) in the genes CYP2C9, which influences metabolism, and VKORC1, which influences pharmacodynamic response (meaning the biochemical and physiological effects of the drug on the body), are strongly associated with warfarin responsiveness [1]. According to an article in Wired Science last year [2]:

Doctors in the field say that traditional measurements such as size and age account for just 15% to 20% of the variability in responses to warfarin. Adding the genetic factors can raise that figure to 50% or higher, say advocates of genetic testing.

Indeed, experts estimate that integrating genetic testing into routine warfarin therapy could avoid 85,000 serious bleeding events and 17,000 strokes annually [3]. Integrated genetic testing in warfarin therapy is estimated to reduce healthcare spending by $1.1 billion U.S. annually.

Helix Health, the first U.S. stand-alone genomic medicine practice, is hosting a 90-minute CliniCast today (Monday, June 30, 2008) from 1:00 — 2:30 PM EDT to examine how genomic medicine improves the accuracy of warfarin dosing. The CliniCast will feature Dr. Steven Murphy (the GeneSherpa) and a panel of medical, scientific and legal experts.

The group will discuss a number of topics:

• Why genetic testing is a necessary feature in anticoagulant therapy.
• What potential risks exist in “Trial and Error” dosing?
• Will insurance cover this genetic testing?
• What are potential tort issues in predictive genetic testing and medical uses of genetic tests associated with anticoagulant therapy?
• Why aren’t physicians utilizing FDA approved testing and dosage guidance?

To register for the free webcast, point your browser here: http://event.netbriefings.com/event/helixhealth/Live/warfarin/register.html

A podcast of the CliniCast will be available on Helix Health following the session. For more information, contact info@helixhealth.org or visit Helix Health.

Additional resources can be found in the Personalized Medicine category of the Highlight HEALTH Web Directory.

There are a number of genetic tests currently available that can help predict response to certain medications. Clinical studies are currently being conducted to understand the connection between genotype and warfarin dose for the delivery of optimized anticoagulant therapy. Given the widespread use of warfarin, I anticipate an interesting discussion on the Helix Health CliniCast and encourage everyone to register and attend.

References

1. Cooper et al. A genome-wide scan for common genetic variants with a large influence on warfarin maintenance dose. Blood. 2008 Jun 5. [Epub ahead of print]
   View abstract
2. Genomic Medicine Hits Mainstream Milestone. Wired Science. 2007 Aug 17.
3. Health Care Savings from Personalizing Medicine Using Genetic Testing: The Case of Warfarin. Andrew McWilliam, Randall Lutter, Clark Nardinelli. Working Paper 06-23. 2006 Nov.