QUESTION: Can I administer IV vitamin C to a patient on Warfarin?
ANSWER: Concern exists over the use of IV Vitamin C and Warfarin. Oral vitamin C in two cases were reported to interfere with a patient taking Warfarin. Other reviews did not find significant concern and in fact reported a high threshold of safety. A quick review of the proposed mechanism is warranted: Warfarin is thought to interfere with clotting factor synthesis by inhibition of the C1 subunit of vitamin K epoxide reductase (VKORC1) enzyme complex, thereby reducing the regeneration of vitamin K1 epoxide. In sum, creating a block in the recycling of Vitamin K (or why Warfarin could inhibit all the Vitamin K dependent clotting enzymes). A reductase enzyme may in fact be supported by an antioxidant so theoretically any added antioxidant activity may reduce the Warfarin effect (although reference 4 argues against this idea). In its pro-oxidant use as a high dose IV Vitamin C infusion the effect if anything (using this logic) would support the Warfarin reductase blockade. In many thousands of IV Vitamin C infusions with those concurrently taking Warfarin I have not witnessed changes in bleeding or clotting times, nor any clotting based lab values over time. As the case reports exist and one must use caution we always ramp up the high dose IV Vitamin C (normally 25 grams per sequential dose) and watch the patient for any effects. To date none have occurred in our experience.
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