Vitamin K - Anticoagulant Drug Interactions

Anticoagulant Drug Interactions

Phylloquinone (K₁) or menaquinone (K₂) are capable of reversing the anticoagulant activity (incorrectly but colloquially referred to as "blood-thinning action") of the powerful anticoagulant warfarin (tradename Coumadin). Warfarin works by blocking recycling of vitamin K, so that the body and tissues have lower levels of active vitamin K, and thus a deficiency of the active vitamin.

Supplemental vitamin K (for which oral dosing is often more active than injectable dosing in human adults) reverses the vitamin K deficiency caused by warfarin, and therefore modulates or totally reverses the intended anticoagulant action of warfarin and related drugs. Foods containing high amounts of vitamin K (green leafy vegetables) are avoided when taking warfarin. Sometimes small amounts of vitamin K (one milligram per day) are given orally to patients taking Coumadin so that the action of the drug is more predictable. The proper anticoagulant action of the drug is a function of vitamin K intake and drug dose, and (due to differing absorption) must be individualized for each patient. The action of warfarin and vitamin K both require two to five days after dosing to have maximum effect, and neither Coumadin or vitamin K shows much effect in the first 24 hours after they are given.

The newer anticoagulant Pradaxa has a different mechanism of action that does not interact with vitamin K, and may be taken with supplemental vitamin K.

Following long term use of Coumadin, supplemental vitamin K may reverse the arterial calcification attendant on the long-term blockade of vitamin K.{}