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UPDATE: Warfarin Genetic Testing Decreases Hospitalization Rate, Study Finds

This article has been updated to include comments from the ACC meeting.

By a GenomeWeb staff reporter

NEW YORK (GenomeWeb News) – Genetic testing for variants related to warfarin treatment response decreased hospitalization rates by almost one third in a prospective study of patients at sites across the country, according to research being presented today at the American College of Cardiology's scientific session in Atlanta.

Researchers from Medco Health Solutions, the Medco Research Institute, and the Mayo Clinic led the comparative-effectiveness study, which looked at the utility of genetic testing for improving the safety and effectiveness of the widely prescribed blood thinner warfarin (marketed as Coumadin by Bristol-Myers Squibb and Jantoven by Upsher-Smith). The research was funded by Medco and the Mayo Clinic's Center for Individualized Medicine.

Warfarin dosing can be challenging given variable drug response between individuals and a narrow therapeutic range for the drug: doses that are too high or too low can lead to bleeding or clotting complications, respectively. Consequently, the US Food and Drug Administration requires a black box warning on warfarin labels outlining such risks and recommending close patient monitoring.

Last month the FDA also updated warfarin labeling to include genetic testing recommendations as well. As GenomeWeb Daily News sister publication Pharmacogenomics Reporter reported in February, the labeling now refers to a table outlining recommended doses for individuals depending on their CYP2C9 and VKORC1 genotype information.

For the current study, which began in July 2007, researchers enrolled patients from 49 states who were insured by dozens of health plan sponsors managed by Medco.

Using Medco's integrated medical and pharmacy claims systems, the team compared 896 individuals who received genetic testing for CYP2C9 and VKORC1 genes early in their warfarin treatment with 2,688 control individuals, selected from the same group of health insurance sponsors the previous year, who had received treatment without genetic testing.

Patients participating in the study ranged from 40 to 75 years old, with an average age of 65 years old. Around 60 percent of participants in the study and controls groups were men. Genetic testing for the study was performed at the Mayo Clinic, which also gave doctors guidelines for applying genetic information to drug dosing and management.

The researchers found that those in the genetic testing group were 28 percent less likely to be hospitalized for bleeding or thromboembolism — and 31 percent less likely to be hospitalized for any reason — than individuals in the control group, based on medical claim data.

"These results show that we can greatly reduce hospitalizations, and their significant costs, by making genetic testing routine early in a patient's therapy with warfarin," lead author Robert Epstein, Medco's chief medical officer and president of the Medco Research Institute, said in a statement. "If it costs a few hundred dollars for the genetic test but avoids the $13,500 hospital bill, it very quickly pays for itself."

However, according to a review presented at the ACC meeting by Mandeep Mehra, chief of cardiology at the University of Maryland Medical Center, the design of the Medco/Mayo study did not sufficiently account for the fact that physicians, aware that their patients were being genotyped as part of a clinical trial, may have followed those patients more closely, leading to better outcomes.

While Epstein acknowledged that physicians knew their patients were being genotyped, he also said the fact that physicians in the Mayo/Medco study may have followed their patients more closely because of genetic testing shouldn't be a mark against the clinical utility of the intervention.

"If, in fact, receiving genotyping information helps the physician pay closer attention to the patient, like make them do more INRs because it points out the person has a rare genotype and needs to be tracked closer, I don't think that's a bad thing," he said.

Down the road, researchers reportedly plan to look at the cost-benefit profile of warfarin genetic testing.


Turna Ray contributed additional reporting for this article from the ACC meeting. A detailed article on Medco's presentation and Mehra's review can be found on Pharmacogenomics Reporter.

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