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The relationship between inhibition of vitamin K1 2,3‐epoxide reductase and reduction of clotting factor activity with warfarin.
Author(s) -
Choonara IA,
Malia RG,
Haynes BP,
Hay CR,
Cholerton S,
Breckenridge AM,
Preston FE,
Park BK
Publication year - 1988
Publication title -
british journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.216
H-Index - 146
eISSN - 1365-2125
pISSN - 0306-5251
DOI - 10.1111/j.1365-2125.1988.tb03274.x
Subject(s) - warfarin , clotting factor , vitamin k epoxide reductase , vitamin , chemistry , factor vii , pharmacology , medicine , endocrinology , metabolism , coagulation , biochemistry , cytochrome p450 , atrial fibrillation , cyp2c9
1 The effect of low dose steady state warfarin (0.2 mg and 1 mg daily) on clotting factor activity and vitamin K1 metabolism was studied in seven healthy volunteers. 2 Steady state plasma warfarin concentrations were 41‐99 ng ml‐1 for the 0.2 mg dose and 157‐292 ng ml‐1 for the 1 mg dose. 3 There was a significant prolongation of the mean prothrombin time (0.9 s) after 1 mg warfarin daily, but no significant change in prothrombin time after 0.2 mg warfarin daily. There was no significant change in individual clotting factor activity (II, VII, IX or X) with either dose of warfarin. 4 Following the administration of a pharmacological dose of vitamin K1 (10 mg), all seven volunteers had detectable levels of vitamin K1 2,3‐epoxide with both doses of warfarin (Cpmax 31‐409 ng ml‐1). 5 Both the Cpmax and the AUC for vitamin K1 2,3‐ epoxide were significantly greater on 1 mg of warfarin daily than 0.2 mg daily (P less than 0.01). 6 The apparent dissociation between inhibition of vitamin K1 2,3‐epoxide reductase and reduction of clotting factor activity, produced by warfarin, may reflect the insensitivity of functional clotting factor assays to a small reduction in clotting factor concentration.