Kinetic Study of Factor X During Oral Anticoagulation with Acenocoumarol: Potential Value for the Initiation of Treatment

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Abstract
We measured prothrombin time and coagulation factors (F) VII and X in 19 patients under heparin treatment receiving acenocoumarol (3 mg per day) without a loading dose. Blood samples were obtained on the 1st (D0), 2nd (D1), 3d (D2), 5th (D4), 7th (D6) and 9th (D8) days of treatment. In 7 patients (group A) acenocoumarol dosage had to be reduced at D2, D4, or D6, based on a prothrombin time smaller than 25% of normal. In the remaining 12 patients (group B), FVII and prothrombin time followed a double exponential decline. Conversely, the FX decrease could be fitted to a single exponential pattern. The slope of the linear relation, loge (FX) = b - a (D), calculated from measurements made at D0, D1, and D2, allowed us to predict the FX level at D8 by simple extrapolation, and, consequently, to estimate as early as D2 whether a change of acenocoumarol dosage would have been required. In group A this extrapolation always announced a dangerously low FX concentration at Dg that justified the preventive reduction of acenocoumarol dosage. We conclude that FX can be a valuable guide in the initiation of an oral anticoagulant treatment.

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