Serious hemorrhage is a constant threat to patients receiving coumarin anticoagulants. While life-threatening bleeding is not common, the physician should be aware of the possibility of such a complication and take every possible precautionary measure. Moreover, these drugs should not be used unless the benefit to be obtained outweighs the possible threat to life.
The coumarin derivatives alter the concentration of the coagulation factors in the plasma by interfering with their synthesis by the liver. At one time it was thought that the chief effect was on prothrombin concentration but it is now known that the concentration of factors VII, IX, and X are also reduced. The one-stage prothrombin time is still widely used in this country as a measure of the effect of these drugs on coagulation although it is not specific for a single coagulation factor. Specific tests for the various factors have not been sufficiently useful to
Ebert RV. Oral Anticoagulants and Drug Interactions. Arch Intern Med. 1968;121(4):373-374. doi:10.1001/archinte.1968.03640040067015