LETTER
Warfarin: Less May Be Better
Paul R. Casner, MD, PhD
15 August 1997 | Volume 127 Issue 4 | Page 332
TO THE EDITOR:
In their report on loading doses of warfarin therapy, Harrison and colleagues [1] concluded that a 5-mg loading dose of warfarin produced less excess anticoagulation than a 10-mg loading dose. The authors base this conclusion on the fact that fewer patients in the 5-mg group than in the 10-mg group had an INR greater than 3.0. Because the specific values of the greater-than-3.0 INRs are not given, we do not know whether these elevations are clinically significant. For example, INRs of 3.1, 3.2, or 3.3 could be classified as "excess anticoagulation," but these elevations are not clinically significant.
The authors also state that more patients in the 10-mg group than patients in the 5-mg group received vitamin K (4 compared with 1). Vitamin K was administered to these patients because their INRs ranged from 4.8 to 9.3. However, none of the patients bled. Many clinicians would not administer vitamin K to such patients, particularly if the INRs were less than 6.0 [2]. Finally, the study began with 49 patients-24 patients receiving the 5-mg dose and 25 patients receiving the 10-mg dose. At the end of the study. 17 patients remained in the 5-mg group and 18 remained in the 10-mg group. What happened to the other 14 patients?
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Author and Article Information
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Texas Tech University Health Sciences Center; El Paso, TX 79905
1. Harrison L, Johnston M, Massicotte MP, Crowther M, Moffat K, Hirsh J. Comparison of 5-mg and 10-mg loading doses in initiation of warfarin therapy. Ann Intern Med. 1997; 126:133-6.
2. Hirsh J, Dalen JE, Deykin D, Poller L, Bussey H. Oral anticoagulants: mechanism of action, clinical effectiveness. and optimal therapeutic range. Chest. 1995; 108(4 Suppl):231S-46S.
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