Use of oral vitamin K₁ by patients taking warfarin sodium: Experience in an ambulatory care clinic

Background and Objective: Warfarin sodium dosing is adjusted according to the patient's international normalized ratio (INR). On occasion, the INR may be greater than 5.0, and during this time patients experience increased risk of bleeding. The use of oral vitamin K₁ has been recommended in this situation, but the tablet formulation of vitamin K₁ is not marketed in Canada. This report describes the use of vitamin K₁ (in tablet form) to reduce high INR values in patients receiving warfarin sodium. Methods: Patients of a Canadian ambulatory care clinic were given 5-mg tablets of vitamin K₁ (phylloquinone; Mephyton, Merck Frosst Canada, Kirkland, Quebec) through special arrangement with Health Canada's Health Protection Branch. They were instructed to take the vitamin K₁ according to an agreed close schedule, if an INR test result above 5.0 was reported. In such instances, the INR test was repeated the following clay. Results: A total of 47 INR test results above 5.0 were reported in 39 patients over a 21-month period. None of the patients reported bruising or bleeding. On 31 of these occasions, 2.5 mg of vitamin K₁ was taken, and the mean INR fell from 6.8 (range 5.1 to 8.6) to 2.9 (range 1.4 to 5.9) within 24 h. On 6 occasions, 5.0 ing of vitamin K₁ was taken, because the INR value was greater than 9.0; in these cases the mean INR fell from 11.3 (range 9.5 to 13.8) to 2.5 (range 1.8 to 3.9). Data for the remaining 10 INR results were not evaluable. Conclusions: For ambulatory patients taking warfarin sodium, oral vitamin K₁ can be used to reduce a high INR value without the need for a clinic visit.