DALLAS – Genotyping to guide the starting dosage of warfarin treatment showed no added value above tailoring treatment with a panel of clinical features in a randomized, controlled U.S. trial of more than 1,000 patients.
The resounding null result from adding genotype information should spell the end of this practice, said Dr. Stephen E. Kimmel, lead investigator for the study, and professor and director of cardiovascular epidemiology at the University of Pennsylvania in Philadelphia.
"Based on what we’ve seen, I don’t believe there is sufficient evidence to add genetic information on top of the available clinical algorithms," Dr. Kimmel said at the American Heart Association scientific sessions. "I don’t think we’ll see another genetics trial in warfarin treatment. I think this is it."
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Good outcomes in the comparison group largely accounted for the failure of genotyping to significantly improve the percentage of time that patients’ international normalized ratios (INRs) were in the target range of 2.0-3.0. The amount of time in the therapeutic INR range (PTTR) averaged 45% in patients in the comparison arm during the first 4 weeks of warfarin treatment.
"When the comparison group does so well, it’s more difficult for genotyping to have an effect," said Dr. Elaine M. Hylek, professor of medicine and an anticoagulant specialist at Boston University.
That limitation, coupled with the shifting anticoagulant landscape, knock genotyping out of the picture, she agreed. "It will be difficult funding [another study of genotyping] with all the anticoagulant alternatives that are now out there" for preventing thrombosis in patients with atrial fibrillation or a recent venous thromboembolism.
Mitchel L. Zoler/Frontline Medical Communications
Dr. Stephen E. Kimmel
The Clarification of Optimal Anticoagulant through Genetics (COAG) trial enrolled 1,015 patients initiating warfarin therapy at 18 U.S. centers during September 2009 to April 2013. The study randomized patients to two different ways to calculate their warfarin dosage during the first 5 days of treatment. Half had their dosage calculated by a formula that took into account seven clinical and demographic factors, including age, race, smoking status, and body surface area. The others had their dosage calculated with the same formula and factors plus added information on the patient’s genotype for two genes that affect warfarin activity, CYP2C9 and VKORC1. Patients’ average age was 58 years; just over a quarter were African American.
During the first 4 weeks on treatment, the average PTTR was 45% in both arms of the study, the trial’s primary endpoint. Adding genotyping information led to a bigger improvement in the PTTR among the non–African American patients compared with those who were African American, but did not produce a significantly increased PTTR in the non–African American subgroup.
Dr. Munir Pirmohamed reported results from a similar study that enrolled 455 patients starting warfarin therapy at any of five centers in the United Kingdom and Sweden. The EU-Pharmacogenetics of Anticoagulant Therapy (EU-PACT) Warfarin study mainly differed from the COAG study by the background method used to calculate a starting warfarin dosage over the first 3 days of treatment. In EU-PACT, the warfarin dosage of all patients was adjusted for age but not for other factors. In the intervention arm, the starting dosages were adjusted for the status of the same two genes, CYP2C9 and VKORC1.
During the first 12 weeks after starting warfarin, the cumulative average PTTR was 67% in the patients whose dose was adjusted by genotype and 60% in patients who were not genotyped, a statistically significant difference for this study’s primary endpoint, reported Dr. Pirmohamed, professor and head of molecular and clinical pharmacology at the University of Liverpool, England.
Taken together, the findings of the two studies highlight that patients should not start warfarin treatment on a fixed dosage, said Dr. Patrick T. Ellinor, a cardiologist and arrhythmia specialist at Massachusetts General Hospital, Boston, and designated discussant for both reports at the meeting. The findings support use of a clinical algorithm that takes into account several clinical factors, he added.
Concurrently with the meeting, the reports were published online for COAG (N. Engl. J. Med. 2013 [doi:10.1056/NEJMoa1310669]) and for EU-PACT (N. Engl. J. Med. 2013 [doi:10.1056/NEJMoa1311386]).
The COAG and EU-PACT studies did not receive any direct commercial sponsorship. Dr. Kimmel has been a consultant to Pfizer and Janssen. Dr. Hylek has been a consultant or adviser to Bayer, Boehringer Ingelheim, Bristol-Myers Squibb, Daiichi Sankyo, Johnson & Johnson, and Pfizer. Dr. Pirmohamed and Dr. Ellinor had no disclosures.
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