Genetic testing can help determine safest dose of warfarin for joint surgery patients

A new five-year study of nearly 1,600 patients finds that genetic testing can help determine the safest dose of the blood thinner warfarin, with fewer side effects, in patients undergoing joint replacement surgery.

Considering a patient’s genetic makeup when prescribing warfarin—a blood thinner commonly prescribed to prevent life-threatening blood clots—can mean fewer adverse side effects like haemorrhage, researchers found.

Warfarin is a commonly prescribed, very effective anticlotting medicine — but it’s often associated with adverse complications and each patient requires a different dosage to achieve the desired treatment effect.

That unique dosing is based in part on an individual’s genetics, and great interest exists in understanding whether an individual’s genetics can guide how to best prescribe warfarin to reach the optimal therapeutic range.

Now, researchers from Intermountain Medical Center, along with four other research centers, including Washington University School of Medicine in St. Louis, which led the national study, have shown that outcomes greatly improve for older patients who undergo elective hip or knee replacement when the dose of warfarin is based on how a patient’s liver metabolizes the blood thinner, which can be discovered using a blood test.

Researchers say study findings from the GIFT study (Genetics Informatics Trial of Warfarin to Prevent Deep Venous Thrombosis) are significant. Compared to patients who received a standard dose, patients who received genetically-dosed warfarin had a 27 percent reduction in complications.

Specifically, their major bleeding was reduced by 75 percent, the incidence of excessive international normalized ratios was reduced by about 30 percent, and blood clots occurred 15 percent less often. No patients died during the study.

The findings from the GIFT study are published and could be used immediately. The Food and Drug Administration has since 2007 included language in its warfarin packaging that encourages the use of genetic guidance, if it’s available.

“Differences can be identified by looking at a patient’s genetic makeup, and specifically at the genes that are responsible for the liver’s metabolism of the drug,” said Scott Woller, MD, co-director of the Thrombosis Program at Intermountain Medical Center and principal investigator for Intermountain Healthcare.

Intermountain Healthcare