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To the Editor:—
The report on long-term anticoagulant use in acute myocardial infarction (198: Nov 7, 1966, adv p 37) again emphasizes the confusion that exists in this field. One of the principal reasons for difficulty is that the therapeutic range for the depression of prothrombin activity has never been established. Usually, the maintenance dose is based on the empirical rule of keeping the one-stage prothrombin time at about twice normal. While this rule is a fairly trustworthy guide for avoiding untoward effects such as bleeding, it offers no assurance that an effective therapeutic depression of coagulability exists.The fear of hemorrhage in patients receiving anticoagulants is well justified. Bleeding may occur when the prothrombin time is in the desired range. This does not imply that the prothrombin time is unreliable but suggests that another factor has been superimposed. One of these factors is a sudden drastic change in the
Anticoagulants in Myocardial Infarction. JAMA. 1966;198(12):1314. doi:10.1001/jama.1966.03110250128044