Vitamin K and Oral Anticoagulant Drugs as Competitive Antagonists in Man

To determine whether vitamin K and oral anticoagulant drugs act as competitive antagonists in man, various single doses of vitamin K and sodium warfarin were administered to 8 normal subjects. The hypoprothrombinemic response was directly proportional to the warfarin dose and inversely proportional to the vitamin K dose in all instances. Double reciprocal graphs of the data for warfarin alone compared with warfarin and vitamin K showed a common intercept and different slopes in all 8 subjects. It is concluded that vitamin K and oral anticoagulant drugs at therapeutic doses are truly competitive antagonists in man.