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Genetic Testing Improves Warfarin Dosing But Not Optimal Dose in Second Study

Predicting right dose of warfarin for older patient can be tricky; two studies of genetics use in warfarin therapy presented at American Heart Association’s Scientific Session; patients with atrial fibrillation, venous thromboembolism, and in second study stroke history

DALLAS, Nov. 19, 2013 — Obtaining genetic information before starting warfarin therapy helped patients increase the effectiveness of treatment while reducing the risk of over-anticoagulation and improper dosing in a late-breaking clinical trial presented at the American Heart Association’s Scientific Sessions 2013. Another study presented, however, found genetics did not prove useful in predicting optimal doses of warfarin.

Genetic Info Helpful Before Warfarin Therapy

Study Highlights:

In a study conducted in Europe, genetic testing before beginning warfarin therapy helped patients increase their time in therapeutic range by 7 percent while reducing the need for warfarin dose adjustments.

“We found that genotyping before starting warfarin increased the time in therapeutic range by approximately 7 percent, reduced over-anticoagulation, reduced the time required to reach therapeutic range, improved the time required to reach stable dose and reduced the number of warfarin dose adjustments,” said Munir Pirmohamed, M.D., Ph.D., lead author of the study and NHS Chair of Pharmacogenetics at the University of Liverpool in the United Kingdom.

The EU Pharmacogenetics of Anticoagulant Therapy (EU-PACT) Warfarin Study of 454 patients in Europe compared using genetic tests to guide warfarin dosing with traditional methods, which involves patients undergoing frequent blood testing to gauge whether their warfarin levels are too high or too low.


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The majority of patients were white, average age 67 years, 61 percent were male, 72 percent had atrial fibrillation and the other patients had venous thromboembolism. All patients were followed for three months, and were checked at days four, six, eight, 15, 22, 57 and 85 of the study. Adjustments to the patients' warfarin doses were either based on genetic results or standard blood testing to decide whether warfarin levels were too high, too low or just right.

Although warfarin has been approved for decades, there is a lot of variability as to how patients will respond to warfarin. Additionally, finding the right dosage can be difficult — too little warfarin can lead to blood clots and too much can cause bleeding.

Researchers specifically looked for two genes associated with the clotting process.

“Our study very much fits in with the concept of personalized medicine, which aims to get the right drug, at the right dose to the right patient,” Pirmohamed said.

“There is huge potential in the cardiovascular field for personalizing therapy on the basis of genetic or non-genetic tests,” he said. “For genetic testing, in some cases it may be possible to undertake the testing at the bedside or in surgery, so called point-of-care tests as we did in this trial. We need evidence from randomized controlled trials to show the utility of genetic testing.”

Co-authors are Girvan Burnside; Jenni Stoddern; Clare Prince; Cheng Hok Toh; Toby Nicholson; Patrick. Kesteven; Andrea Jorgensen; Anne Daly; Anke-Hilse Maitland-van der Zee; Paula Williamson; Niclas Eriksson; Peter Avery; Farhad Kamali and Mia Wadelius for the EU-PACT Investigators, Disclosures

EU-FP7 Programme funded the study.

Genetics Failed to Take Guesswork Out of Warfarin Dosing

Study Highlights:

  • Genetic testing did not prove useful in improving blood thinning control in patients on warfarin.

  • Both the group undergoing genetic testing and the standard dosing group were within the appropriate therapeutic range — meaning that the blood thinning was within the desired level — 45 percent of the time.

Genetics did not prove useful in predicting optimal doses of warfarin for patients in a  late second late breaking clinical trial presented at the American Heart Association’s Scientific Sessions 2013.

In the Clarification of Optimal Anticoagulation through Genetics (COAG) trial, researchers divided 1,015 patients with histories of stroke, venous thrombosis and atrial fibrillation, who took the common blood-thinning drug warfarin into two groups.

Clinical information, such as age, weight, and smoking status, was used for one group to measure how much warfarin they would need while the second group used similar clinical information plus genetics.

During this multi-center, randomized, double-blinded, controlled study, all patients received warfarin, but one group received therapy based on clinical information, while the other group received therapy guided by their genetic information. Each group received an initial warfarin dose, and then four to five days later, adjustments were made to their doses based on either genetic information or standard clinical information.

Patients were followed for up to six months from 2009-2013.

Regardless of whether or not genetic information was used, the two groups of patients showed no significant differences in outcomes; both groups were within the appropriate therapeutic range — meaning that the blood thinning was within the desired range — 45 percent of the time over the first four weeks. In an additional finding among African Americans, those receiving therapy based on genetics didn’t do as well as those who did not use genetics.

Patients’ average age was 57 years; 51 percent were male; 27 percent were African American; 22 percent had atrial fibrillation, and 58 percent had deep vein thrombosis in the legs or lungs.

“This study demonstrates that until you do a clinical trial, you really don't know what the answer is going to be," said Stephen Kimmel, M.D., lead study author and a professor of medicine and epidemiology at the University of Pennsylvania School of Medicine.

"There's a lot of debate about when to bring genetics into clinical practice, and whether or not you need clinical trials before widely using genetics. For a drug as complex as warfarin, the COAG trial demonstrates the utility of performing such trials.”

Predicting the right dose of warfarin for the individual patient can be tricky; too much can lead to internal bleeding and too little can lead to blood clots, some of which can be life-threatening. Patients taking warfarin have to undergo frequent monitoring to see whether their doses need to be changed. Identifying certain genetic markers from a patient's blood sample is suggested to help improve the initial dosing of warfarin and smooth out the many dose changes often required during monitoring.

One gene is responsible for how warfarin is metabolized by the liver. The other gene is about how the body responds to warfarin. Identifying one or both of these two genes in a patient's blood sample has been suggested to help physicians prescribe more specific warfarin doses that better align with the patient's unique biological makeup.

The National Heart, Lung, and Blood Institute funded the study. GenMark Diagnostics and AutoGenomics Inc. loaned genotype platforms to the study and Bristol-Meyers Squibb donated the study drug.

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