MajorVitamins. γ-glutamyl carboxylase cofactor×Vitamin K antagonist anticoagulants
Updated · Methodology
Mechanism
Menaquinone is vitamin K just as phylloquinone is, with a longer plasma half-life. It antagonises warfarin by the same mechanism, and its presence in calcium plus vitamin D bone complexes means it enters the regimen without the patient registering it as vitamin K.
Symptoms
INR falling below range in the weeks after starting a bone complex, with no change in diet or warfarin dose.
Management
Check the composition of any bone or joint complex before taking it with warfarin: K2 often appears in the small print. If it is already in use, do not stop it abruptly; check the INR more frequently while the decision is made with the prescriber.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- NIH Office of Dietary Supplements: Vitamin K – Health Professional Fact Sheet (2025)– NIH ODS, Vitamin K, Warfarin and similar anticoagulants