• Standardized clotting time (method developed by the authors) and prothrombin activity were measured in 40 patients who were receiving bishydroxycoumarin in the treatment of cardiovascular diseases. The drug gave a reliable prolongation of the clotting time, and when the clotting time was kept within the therapeutic range there were neither thromboembolic complications nor hemorrhagic accidents. All hemorrhagic accidents occurred when the clotting time exceeded 22 minutes. The time relations and correlation coefficients for clotting time and prothrombin activity showed that these tests measure different phases of blood coagulation. The clotting-time test was the more valuable guide in adjusting dosages in anticoagulant therapy.
Mayer GA, Connell WF. EFFECT OF BISHYDROXYCOUMARIN (DICUMAROL) ON CLOTTING TIME OF WHOLE BLOOD. JAMA. 1956;161(9):806–811. doi:10.1001/jama.1956.02970090032007
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