In two studies in patients anticoagulant effects of warfarinwere unchanged by small to large doses of vitamin E, althoughthere is an isolated case of bleeding attributed to concurrent use.In three healthy subjects, effects of dicoumarol were slightlyincreased by vitamin E.
A study in 3 healthy subjects found that 42 units of vitamin E daily for a month increased response to a single dose of dicoumarol after 36 hrs (decrease in prothrombin activity from 52 to 33%) (See reference number 1)
In a double-blind,placebo-controlled study in 25 patients stabilised on warfarin, moderate to large daily doses of vitamin E (800 or 1200 units) for a month caused no clinically relevant changes in prothrombin times and INRs (See reference number 2). Similarly, in another study in 12 patients taking warfarin, anticoagulant effects of warfarin were unchanged by smaller daily doses of 100 or 400 units of vitamin E given for 4 weeks (See reference number 3).
However,in one case, a patient taking warfarin (and multiple other drugs) developed ecchymoses and haematuria, which was attributed to him taking 1200 units of vitamin E daily over a 2-month period. His pro-thrombin time was found to be 36 seconds. A later study in this patient showed that 800 units of vitamin E daily for 6 weeks reduced his blood clotting factor levels, increased prothrombin time from about 21 to 29 seconds, and caused ecchymoses (See reference number 4).
The suggested explanation is that vitamin E interferes with activity of vitamin K in producing blood clotting factors,(See reference number 4,5)and increases in dietary requirements of vitamin K (See reference number 6,7)
Information is limited but evidence suggests that most patients taking warfarin are unlikely to have problems if given even quite large daily doses (up to 1200 units) of vitamin E. Nevertheless isolated case cited here shows that occasionally and unpredictably warfarin effects can be changed. It has been recommended that prothrombin times should be monitored when vitamin E is first given (within 1 to 2 weeks has been rec-ommended) (See reference number 2). The same precautions could be applied to dicoumarol as well. However,as only one case of bleeding has been reported this does seem somewhat over-cautious. Information about other oral anticoagulants is lacking.
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