Effect of vitamin E on prothrombin levels in warfarin-induced vitamin K deficiency.

Rats rendered lightly vitamin K deficient with warfarin (0.01 mg/100 g, IP) and given the equivalent of 1000 units of vitamin E/kg IM for 7 days, showed a marked reduction in functional factor II activity, but normal factor II levels using Echis venom on coagulation analysis. In 12 humans receiving warfarin, vitamin E was administered in doses of 100 or 400 units/day orally for 4 wk. The results in these patients showed no significant change in the prothrombin time, factor II coagulant activity, or factor II antigen (by electroimmunoassay). However, by using a ratio of factor II coagulant activity to immunoreactive protein, significant reduction was observed when compared to pretreatment ratios. These data suggest that vitamin E acts at the step mediated by vitamin K and not in the synthesis of the factor II precursor. Although the administration of high doses of vitamin E in animals, and possibly humans, with vitamin K deficiency potentiates the vitamin K deficiency, this effect is not clinically obvious with 400 IU/day or less.