Potentiation of vitamin K antagonists by high-dose intravenous methylprednisolone

Background: Oral anticoagulants and pulse high-dose intravenous methylpredn isolone are often administered concomitantly, but no data on potential inte ractions 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 methylprednisolon e 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 increa sed to 8.04 (range, 5.32 to 20.0) after methylprednisolone administration. Plasma fluindione concentrations and the INR increased after methylpredniso lone administration. Methylprednisolone alone did not increase prothrombin time. Conclusions: The action of oral anticoagulants is potentiated by intravenou s high-dose methylprednisolone. The INR should be monitored daily during co ncomitant administration of these medications.