High Doses of a Corticosteroid Drug Interfere with Anticoagulant Medicines

Summaries for Patients are a service provided by Annals to help patients better understand the complicated and often mystifying language of modern medicine.

Summaries for Patients are presented for informational purposes only. These summaries are not a substitute for advice from your own medical provider. If you have questions about this material, or need medical advice about your own health or situation, please contact your physician. The summaries may be reproduced for not-for-profit educational purposes only. Any other uses must be approved by the American College of Physicians-American Society of Internal Medicine.

The summary below is from the full report titled "Potentiation of Vitamin K Antagonists by High-Dose Intravenous Methylprednisolone". It is in the 18 April 2000 issue of Annals of Internal Medicine (volume 132, pages 631-635). The authors are N. Costedoat-Chalumeau, Z. Amoura, G. Aymard, O. Sevin, B. Wechsler, P. Cacoub, L.T.H. Du, B. Diquet, A. Ankri, and J.-C. Piette.

What is the problem and what is known about it so far?

Corticosteroid drugs (medicines related to cortisone, a substance produced by the adrenal glands) are commonly used to treat patients with inflammatory diseases or diseases of the immune system. Many of these patients also require treatment with anticoagulant drugs ("blood thinners"). Anticoagulants are used to treat or prevent blood clots (for example, in the brain [strokes], legs [thrombophlebitis], or lungs [pulmonary embolism]). Many drugs can interfere with the action of anticoagulants; some cause them to thin the blood too much, others to thin it too little. Corticosteroids have not been thought to interfere with anticoagulants, but few reports on this issue exist. Methylprednisolone is a commonly used intravenous corticosteroid.

Why did the researchers do this particular study?

To find out if high-dose methylprednisolone given intravenously would make oral anticoagulants thin the blood too much. "Intravenous" means that the drug is given through a small tube inserted into a vein, and "oral" means it is taken by mouth.

Who was studied?

The researchers studied 10 patients who needed to receive high-dose intravenous methylprednisolone at the same time that they were taking oral anticoagulants (either fluindione or acenocoumarol). They also studied 5 patients who received only methylprednisolone.

How was the study done?

The researchers measured the International Normalized Ratio (INR), a blood test that shows how well the anticoagulant is working. The INR should be somewhere between 2.0 to 4.0 for most people on anticoagulants. International Normalized Ratio values lower than 2.0 can put patients at risk for blood clots, and values higher than 4.0 can put them at high risk for bleeding. The researchers also measured the level of anticoagulant drug in the blood before and after the patients started receiving methylprednisolone.

What did the researchers find?

In the patients who were getting both methylprednisolone and anticoagulants, the average INR before methylprednisolone was 2.75 (range, 2.02 to 3.81). After methylprednisolone, the average INR increased to 8.04 (range, 5.32 to 20.0). The patients who got only methylprednisolone did not have increases in the INR. Blood levels of anticoagulant drugs increased after methylprednisolone

What were the limitations of the study?

The study was small and included only patients getting high-dose intravenous methylprednisolone to treat autoimmune or inflammatory diseases. It is unclear whether the results would be the same in patients with other types of diseases or patients who were on lower-dose, oral, or other corticosteroid medications. It is also unclear whether similar results would occur with warfarin, an anticoagulant drug commonly used in the United States.

What are the implications of the study?

High-dose intravenous methylprednisolone can increase the blood levels and action of certain oral anticoagulants. Doctors should consider monitoring the INR frequently in patients who receive these medications together.