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Methylprednisolone: Interaction with Oral Anticoagulants?

Many medications affect the level of anticoagulation achieved by oral anticoagulants. Some case reports have suggested an interaction between corticosteroids and oral anticoagulants, but conflicting results have been reported. French researchers observed a case in which the international normalized ratio (INR) increased after corticosteroids were given; this prompted them to study 10 consecutive patients who took stable doses of oral anticoagulants (for a variety of indications) and who required intravenous hemisuccinate methylprednisolone (2 or 3 doses of 500 or 1000 mg, given over 24 to 72 hours) for various conditions.

Before infusion of methylprednisolone, the patients' mean INR was 2.75. After 2 or 3 doses of methylprednisolone, the mean peak INR was 8.04; the maximum INR occurred after an average of 93 hours. When methylprednisolone was added, in vitro, to the plasma of patients treated with oral anticoagulants, the INR did not change. Five control subjects who received methylprednisolone, but not oral anticoagulants, maintained stable levels of anticoagulation for 7 days.

Comment: High-dose parenteral methylprednisolone appears to potentiate pharmacologic vitamin K antagonism. The mechanism of this effect remains unclear, and none of the study patients received warfarin (they received fluindione or acenocoumarol). Nonetheless, it seems prudent to monitor INRs frequently and to anticipate the need for dose adjustments in patients who receive both oral anticoagulants and high-dose steroids.

— R Saitz

Published in Journal Watch General Medicine May 5, 2000

Citation(s):

Costedoat-Chalumeau N et al. Potentiation of vitamin K antagonists by high-dose intravenous methylprednisolone. Ann Intern Med 2000 Apr 18 132 631-635.

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