Warfarin May Be Safer With Genotype-Guided Dosing: Study

Genetics may play a key role in determining which patients face the greatest risk of bleeding and other side effects from warfarin, a decades-old blood thinner, which is also widely known by the brand name Coumadin. 

In a study published this week the Journal of the American Medical Association (JAMA), researchers looked at patients undergoing hip or knee arthroplasty who were given warfarin to prevent blood clots. The findings suggest that individuals with certain gene expressions, known as genotypes, were more susceptible to bleeding incidents and blood clots when taking the anticoagulant.

The findings come from a clinical trial involving 1,650 patients 65 years old or older, who initiated warfarin treatment after undergoing hip or knee surgery. They were divided into four genotypes.

The surgeries and follow-up occurred at six medical centers nationwide from April 2011 through October 2016. Researchers looked for primary endpoints that included serious bleeding events, venous thromboembolism, or death. Some of the patients were guided through the treatment based on genotype, while others were guided based on internationally accepted target numbers for the amount of warfarin in their bodies.

According to the findings, just under 11% of the patients in the genotype-guided group suffered either bleeding events or thromboembolism, compared to nearly 15% of the clinically-guided warfarin group. Only two of the genotype-guided group suffered major bleeding, compared to eight in the clinically-guided group. The rates of venous thromboembolism were fairly similar, and there were no deaths.

“Among patients undergoing elective hip or knee arthroplasty and treated with perioperative warfarin, genotype-guided warfarin dosing, compared with clinically guided dosing, reduced the combined risk of major bleeding… venous thromboembolism, or death,” the researchers concluded. “Further research is needed to determine the cost-effectiveness of personalized warfarin dosing.”

New Blood Thinner Risks

The findings come as warfarin, which has been on the market for decades, faces stiff competition from a crop of new novel oral anticoagulants, such as Xarelto, Pradaxa and Eliquis. The new drugs, released over just the last few years, have made claims that they are safer and more effective than warfarin, while not requiring the regular blood level monitoring needed with warfarin. However, the new drugs have been linked to serious and sometimes fatal bleeding events as well, and while warfarin’s blood thinning effects can quickly be countered with vitamin K or whole plasma, the new drugs were introduced with no such reversal agents available, making bleeding events much harder to stop.

In July, a report warned that oral anticoagulants were linked to nearly 22,000 reports of serious injuries submitted to the FDA in 2016, and were associated with more than 3,000 reports of deaths.

The report concludes that harm from blood thinners was the highest priority drug safety problem of 2016, due to multiple factors, including the high rate of injury, their widespread use, and the seriousness of the injuries.

Of all of the oral anticoagulants examined, including both new and old drugs, Xarelto bleeding problems were the most common.

More than 18,000 Xarelto lawsuits have been filed against Bayer Healthcare and Janssen Pharmaceuticals, indicating that users suffered severe and uncontrollable bleeding events on the drug.

Given the similar questions of fact and law raised in the complaints, all federal cases are centralized before U.S. District Judge Eldon Fallon in the Eastern District of Louisiana, as part of an MDL or multidistrict litigation.

Similar allegations were raised in thousands of Pradaxa lawsuits filed several years ago, as that other new-generation anticoagulant hit the market before Xarelto. However, the maker of that competing drug ultimately agreed to pay $650 million in Pradaxa settlements just before the first bellwether trials were set to begin, with an average of about $150,000 per claim.

As Xarelto bleeding lawyers continue to review potential cases for individuals prescribed the anticoagulant throughout the United States, the number of complaints has surpassed the number of claims involved in the Pradaxa litigation, as the drug has become more widely used in recent years.