Potentiation of Vitamin K Antagonists by High-Dose Intravenous Methylprednisolone

BACKGROUND: Oral anticoagulants and pulse high-dose intravenous methylprednisolone are often administered concomitantly, but no data on potential interactions are available. OBJECTIVE: To assess possible potentiation of oral anticoagulation by high-dose intravenous methylprednisolone. DESIGN: Prospective cohort study. SETTING: University hospital in Paris, France. PATIENTS: 10 consecutive patients concomitantly receiving methylprednisolone and oral anticoagulants (fluindione and acenocoumarol) and 5 consecutive controls receiving methylprednisolone alone. MEASUREMENTS: Serial determinations of the international normalized ratio (INR) and clotting factors during administration of pulse methylprednisolone. The total plasma fluindione concentration was determined in 3 patients. RESULTS: The mean INR was 2.75 (range, 2.02 to 3.81) at baseline and increased to 8.04 (range, 5.32 to 20.0) after methylprednisolone administration. Plasma fluindione concentrations and the INR increased after methylprednisolone administration. Methylprednisolone alone did not increase prothrombin time. CONCLUSIONS: The action of oral anticoagulants is potentiated by intravenous high-dose methylprednisolone. The INR should be monitored daily during concomitant administration of these medications.