What is My Dose of Coumadin (warfarin) Today?


If you take Coumadin (warfarin) to prevent blood clots, you probably know that you need periodic blood tests to make sure the dose of your medicine is correct. After your doctor reviews the results of these tests, he may ask you to take more or less of the medicine. Sometimes your doctor may even tell you to stop taking the medicine for a few days, or until your next blood test.

A mistake caused by this kind of confusion happened recently to a man taking warfarin. Whenever a dose change had been needed before, his doctor had always called him and told him how many of his 5 mg warfarin tablets to take. But on this occasion, his doctor simply told him to take 7.5 mg every day. The doctor did not specify that he should break one of his 5 mg tablets in half and take 1 1/2 of the tablets. The man instead took 7 1/2 of his 5 mg tablets daily. This was 5 times more medicine than he should have been taking. Taking too much warfarin can lead to serious bleeding. Fortunately, the man’s routine office visit was 2 days later, and his doctor discovered the error.

Taking too little warfarin can also cause serious problems. Another man developed a blood clot in his leg after his doctor told him to stop taking warfarin. His most recent blood test had shown that his current dose was too high. The doctor told the man to stop taking warfarin, and to have another blood test 3 days later. But after that blood test was done, the doctor forgot to call the man back to tell him how much warfarin to start taking again. The man didn’t take warfarin for a week, and then developed a blood clot.

Follow these suggestions to avoid errors when the doctor changes your Coumadin (warfarin) dose:

Keep a record of telephone calls. When your doctor calls to make a change in your warfarin dose: write down the dose and any other directions during the call, read the dose and instructions back to the doctor to make sure you understand them correctly; date the instructions so they won’t be mixed up with older instructions.

Know your dose. Always tell your doctor the strength of warfarin tablets that you have on hand. Then ask him to tell you how much warfarin to take, and how many tablets in that strength to take to equal the dose. If you are running low on tablets, ask for a new prescription. Keep instructions nearby. Keep the dated instructions near the reveal changes.

Tell your doctor if there has been a recent change in your diet or if you are taking any new medicines. Certain foods (green vegetables, green teas) and medicines can change the way that warfarin works in your body.

Call your doctor. If your doctor told you to stop taking warfarin until your next blood test, call him if you don’t hear from him within 24 hours of the test to find out your new dose.

Created on September 1, 2004

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