Anticoagulation in a Patient with Mechanical Valve and Bleeding Risk
A 70-year-old woman with a mechanical mitral valve (target INR 2.5–3.5) on warfarin presents with melena and a hemoglobin drop from 12 to 8.5 g/dL. She also takes aspirin 81 mg, omeprazole, and recently started fluconazole for a vaginal yeast infection. Her INR is 6.8. She is hemodynamically stable but has ongoing melena. The team debates holding warfarin, giving vitamin K, and whether to add a PPI or stop aspirin.
1. Explain the interaction with fluconazole and its contribution to the supratherapeutic INR.
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Fluconazole is a potent CYP2C9 (and CYP3A4) inhibitor. Warfarin's more potent S-enantiomer is metabolized primarily by CYP2C9, so fluconazole markedly reduces warfarin clearance and raises INR - a well-described interaction, especially at higher fluconazole doses. Combined with aspirin (antiplatelet, GI injury) and possibly omeprazole (CYP2C19 effects, minor), the bleeding risk is compounded. The INR of 6.8 with melena indicates over-anticoagulation plus GI bleeding; fluconazole is the likely precipitant.
2. Decide on reversal: should she receive vitamin K and/or prothrombin complex concentrate? Justify.
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She has clinically significant GI bleeding with INR 6.8, so reversal is indicated. Give vitamin K 5–10 mg IV (slow infusion) plus 4-factor prothrombin complex concentrate (PCC) or fresh frozen plasma if PCC is unavailable, to rapidly correct INR. Hold warfarin. Because she has a mechanical mitral valve, avoid over-reversal that could cause valve thrombosis - use the lowest effective PCC dose and recheck INR frequently. Do not use large doses of vitamin K repeatedly, which can cause prolonged warfarin resistance and thromboembolism. Resume warfarin when hemostasis is achieved, at a reduced dose, with bridging as needed.
3. Outline the post-bleeding plan: drug changes, monitoring, and prevention.
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- Stop fluconazole; treat the yeast infection with a non-interacting alternative (e.g., topical clotrimazole or a single-dose oral agent with less CYP2C9 inhibition, depending on susceptibility). 2) Hold aspirin during active bleeding; reassess indication (primary vs secondary prevention) and restart only if benefit outweighs bleeding risk, possibly with gastroprotection. 3) Continue omeprazole for GI protection and treat H. pylori if present. 4) Resume warfarin at a reduced dose when bleeding stops, target INR 2.5–3.5, with frequent INR checks (every 2–3 days initially) because fluconazole's effect may persist. 5) Monitor CBC, iron studies, and stool. 6) Counsel on avoiding NSAIDs, alcohol, and interacting drugs; use an anticoagulation clinic; consider a DOAC is not appropriate for mechanical valves - warfarin remains standard.