Vitamin K for Warfarin-Induced Hypocoagulation
Low-dose vitamin K conferred no more clinical benefit than placebo, despite lowering INRs more rapidly.
Patients who over-respond to warfarin are often treated with vitamin K, which quickly lowers INR. Investigators at 14 anticoagulation clinics in Canada, the U.S., and Italy conducted a randomized, placebo-controlled trial to find out whether low-dose oral vitamin K (1.25 mg) would reduce bleeding events in patients with INRs between 4.5 and 10.0 on warfarin. Patient characteristics did not differ significantly between the two groups, and all patients were treated with vitamin K (n=355) or placebo (n=369), as allocated.
Ninety days after enrollment, 56 (15.8%) of the vitamin K recipients and 60 (16.3%) of the placebo recipients had had a bleeding event; such events occurred within 7 days in 28 (7.9%) and 34 (9.2%) patients in the vitamin K and placebo groups, respectively. Major bleeding occurred in nine vitamin K recipients and four placebo recipients. An analysis stratified by center did not affect the results. Thromboembolism occurred in four vitamin K recipients (1.1%) and three placebo recipients (0.8%). INR decreased more rapidly in vitamin K recipients than in placebo recipients. The average reduction in INR was 1.4 units in the placebo group and 2.8 units in the vitamin K group, a statistically significant difference. In patients aged 70 or older (200 vitamin K recipients and 188 placebo recipients), the rates of bleeding events, thromboembolism, and death did not differ significantly between the two treatment arms.
In this multicenter, randomized trial, vitamin K did, indeed, lower INR more and faster than placebo did, but those effects did not lead to fewer major bleeding events. These results suggest that simply stopping warfarin may suffice to treat patients with elevated INRs.
Joel M. Gore, MD
Published in Journal Watch Cardiology March 4, 2009
Citation(s): Crowther MA et al. Oral vitamin K versus placebo to correct excessive anticoagulation in patients receiving warfarin: A randomized trial. Ann Intern Med 2009 Mar 3; 150:293.