Need for Warfarin is in the Genes

Warfarin less needed by certain African Americans who suffer from blood clots

(RxWiki News) DNA varies from person to person and, in some ways, group to group. Those variations may explain why many blacks require much less of a widely prescribed blood thinner than do whites.

A genetic variant pinpointed through a new study was associated with black patients’ need for a significantly lower dosage of warfarin, whose brand name is Coumadin.

Warfarin is used by many as an effective medication for heart, stroke and other patients who have had blood clots or who are at higher risk for getting them. But warfarin is also responsible for a third of hospitalizations for bad reactions to medicine among people over 65 in the United States, the researchers wrote.

"Ask your pharmacist about the correct medicine dosage."

Minoli Perera, PharmD, of the University of Chicago Department of Medicine, was the study’s lead author.

Her research team conducted genetic testing on an initial set of 533 blacks who were at least 18 years old, and a second, follow-up genetic screening of 432 blacks of the same age range. Patients were recruited at the University of Alabama at Birmingham and through International Warfarin Pharmacogenetics Consortium sites.

Forty percent of patients in both groups had the genetic variant, labeled as rs12777823. It is what’s known as a single nucleotide polymorphism.

Compared to those without that genetic variant, rs12777823 carriers needed from 6.92 fewer milligrams per week to 9.34 fewer milligrams per week of the blood-thinning drug.

Knowing about those genetic details helped doctors improve “...the predictability of warfarin dosing by 21 percent in these individuals,” according to researchers.

That’s good news to some.

“Dosing warfarin appropriately has historically been very challenging, given the variables which can influence the kinetics of this drug,” said Jason Poquette, BPharm, RPh, founder of Blackstone Valley Pharmacy Services, a Massachusetts-based drug retailer and consultancy for patients and others.

“This study," he continued, “identified a single nucleotide polymorphism related to chromosome 10 — specifically rs12777823 — which had a significant impact on warfarin dosing requirements...Although newer anticoagulants are being introduced to the market, the relative affordability of warfarin makes it likely to be used for quite some time into the future.”

According to Mark Newberry, PharmD, of Tarrytown Pharmacy in Austin, TX, “Warfarin has been prescribed to prevent clotting disorders in all races and genders for decades. When prescribed correctly, and monitored appropriately, warfarin can be a very useful medication.”

The researchers wrote that their finding should inform how physicians treating post-surgical heart patients, those with irregular heartbeats and a history of blood clotting decide what is the proper dosage for a racial array of patients.

These study results have “...the potential to increase the safety and effectiveness of this notoriously hard to dose drug," Julie Johnson, PharmD, of the University of Florida’s Department of Pharmacology and Translational Research, one of the researchers, said in a press release from The Lancet.

The study was published June 4 in The Lancet.

The National Institutes of Health, American Heart Association, Howard Hughes Medical Institute, Wisconsin Network for Health Research and the Wellcome Trust funded the study.

The authors reported several potential conflicts of interest regarding their roles in the study, including being paid and unpaid pharmaceutical consultants and serving as investigators in previous clinical trials of warfarin.

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Review Date: 
May 31, 2013