## Clinical Scenario Analysis **Key Point:** The patient's elevated INR (8.5, above therapeutic range) has normalized or decreased despite continued warfarin use, resulting in bleeding. The temporal correlation with increased leafy green intake is the critical clue. ## Vitamin K and Warfarin Mechanism ### Warfarin's Mechanism Warfarin inhibits the vitamin K-dependent carboxylation of: - Prothrombin (Factor II) - Factor VII - Factor IX - Factor X This reduces their γ-carboxylated (active) forms, prolonging PT-INR. ### Vitamin K's Counter-Effect **High-Yield:** Vitamin K (phylloquinone from plants) is a cofactor for the enzyme γ-glutamyl carboxylase. It enables post-translational carboxylation of glutamic acid residues on clotting factors, making them biologically active. **Mnemonic:** **PIVKA** = Proteins Induced by Vitamin K Absence (the inactive, undercarboxylated forms that accumulate when vitamin K is deficient or warfarin is given). ## Drug–Nutrient Interaction ```mermaid flowchart TD A[High dietary vitamin K intake]:::action --> B[Increased hepatic vitamin K pool] B --> C[Enhanced γ-carboxylation of clotting factors] C --> D[More active prothrombin & other factors] D --> E[Warfarin's anticoagulant effect reduced]:::outcome E --> F[INR decreases toward normal]:::outcome F --> G[Loss of anticoagulation → thrombotic risk]:::urgent ``` ## Clinical Pearl **Warning:** Patients on warfarin should maintain **consistent** (not zero) vitamin K intake. Sudden increases (as in this case with leafy greens) or decreases both destabilize INR. The standard advice is "eat vitamin K consistently, not excessively." ## Management 1. Counsel patient on vitamin K consistency 2. Do NOT stop warfarin abruptly 3. Recheck INR in 3–5 days 4. Adjust warfarin dose upward if INR remains subtherapeutic 5. Aim for stable INR 2–3 with stable dietary vitamin K [cite:Harrison 21e Ch 139; KD Tripathi 8e Ch 46]
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