High Doses of a Corticosteroid Drug Interfere with Anticoagulant Medicines. Ann Intern Med. 2000;132:631. doi: 10.7326/0003-4819-132-8-200004180-00038
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Published: Ann Intern Med. 2000;132(8):631.
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.
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.
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.
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.
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
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.
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.
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