28 September 2017

Genetic testing could make warfarin safer

While warfarin is beneficial to patients with high stroke risk, there are other risks involved.

The anti-clotting drug warfarin is often used to reduce stroke risk in patients with a heart rhythm disorder called atrial fibrillation.

This might be a benefit, but since warfarin thins the blood, it carries the risk of bleeding. 

Now a new study reports that genetic testing can improve the safety of the blood thinner warfarin.

Patient's genes determines effect

Warfarin (Coumadin, Jantoven) is often prescribed to prevent life-threatening blood clots in high-risk patients. However, a patient's genes can influence how warfarin is processed in the body. Too little warfarin will not prevent blood clots while too much can trigger internal bleeding, the researchers explained.

Warfarin is "a widely used anticoagulant, but it causes more major adverse events than any other oral drug. Thousands of patients end up in the emergency department or hospital because of warfarin-induced bleeding. But we continue to prescribe it because it is highly effective, reversible and inexpensive," said study first author Dr Brian Gage. He is a professor of medicine at Washington University School of Medicine in St. Louis.

The researchers said they found that by looking for variants in three genes, it's possible to make warfarin therapy safer.

What the study entailed

Variants in one gene affect vitamin K recycling (vitamin K is needed for blood clotting). Variants in another gene affect warfarin sensitivity. And variants in the third gene affect warfarin metabolism in the liver and can cause an overdose if the dose is not adjusted quickly enough, the researchers said.

The study included about 1 600 people 65 and older at high risk for blood clots after undergoing hip or knee replacement surgery. They were randomly assigned to receive either warfarin dosing based on standard clinical factors such as age, height and weight, or dosing based on those clinical factors plus variants in the three genes.

At least one adverse event (bleeding, blood clots in the veins or warfarin overdoses) occurred in 15 of patients dosed in the traditional way and in 11% of patients whose dosing was guided by genetic testing – a 27% difference.

Along with the three variants analysed in this study, there "are additional genetic variants that may help to guide warfarin dosing, especially among patients with African ancestry. In the future, we hope to quantify how these variants affect warfarin," Gage said in a school news release.

High cost involved

One drawback to the testing may be cost.

"Although genetic testing is more expensive than clinical dosing, the cost is falling. In our study, we estimated that genetic testing costs less than $200 (± R2 700) per person, which is less than one month of a newer anticoagulant," Gage noted.

The study was published in the Journal of the American Medical Association.

Managing warfarin

While genetic testing for warfarin is only being studied and will be very expensive to conduct, there are ways to manage the risk of warfarin. Health24 suggested the following in a previous article:

  • Be mindful of what you eat, since some foods might influence the effect of warfarin.
  • Go for regular blood tests.
  • Consult your doctor when you are taking over-the-counter medications to discuss their effect on warfarin.

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