Vitamin K Reverses Overanticoagulation with Warfarin More Quickly When Given by Mouth Than by Injection

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The summary below is from the full report titled "Oral Vitamin K Lowers the International Normalized Ratio More Rapidly Than Subcutaneous Vitamin K in the Treatment of Warfarin-Associated Coagulopathy. A Randomized, Controlled Trial." It is in the 20 August 2002 issue of Annals of Internal Medicine (volume 137, pages 251-254). The authors are MA Crowther, JD Douketis, T Schnurr, L Steidl, V Mera, C Ultori, A Venco, and W Ageno.

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

Warfarin is a medicine that "thins" the blood, making it take longer to coagulate. Doctors prescribe warfarin to treat or prevent several common medical conditions, including blood clots and stroke. Patients taking warfarin need to have blood tests called international normalized ratios (INRs) to check that the amount of warfarin they are taking is thinning their blood an appropriate amount. When the INR is too low (underanticoagulation), clots can occur; when it is too high (overanticoagulation), serious bleeding can occur. When patients become overanticoagulated while taking warfarin, doctors temporarily stop the warfarin. They also sometimes start treatment with vitamin K to speed the reversal of warfarin's effects. It is not known whether giving vitamin K by mouth or by injection brings the INR into the desired range more quickly.

Why did the researchers do this particular study?

To find out whether vitamin K reverses overanticoagulation due to warfarin more quickly if it is given by mouth or if it is given by injection.

Who was studied?

51 patients who were taking warfarin and became overanticoagulated.

How was the study done?

The researchers assigned patients at random to get 1 milligram of vitamin K either by mouth or by injection and measured each patient's INR the next day. They also followed patients for 1 month to see whether they developed any blood clots or bleeding.

What did the researchers find?

Of the 26 patients who got vitamin K by mouth, 15 had INR values in the desired range the next day compared with only 6 of 25 patients who got vitamin K by injection. During the 1-month follow-up period, no patient developed blood clots or serious bleeding.

What were the limitations of the study?

First, this study did not include a group of patients who stopped warfarin without taking vitamin K, so it does not tell us whether giving vitamin K in addition to stopping warfarin is a better way to reverse overanticoagulation than simply stopping warfarin. Second, these results may not apply to overanticoagulated patients who are having active bleeding complications. Third, vitamin K pills are not currently available in North America, so vitamin K can be given by mouth only in liquid form.

What are the implications of the study?

Doctors should consider oral administration when prescribing vitamin K for patients on warfarin who become overanticoagulated.