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Effect of warfarin on plasma concentrations of vitamin K dependent coagulation factors in patients with stable control and monitored compliance
Author(s) -
Kumar S.,
Haigh J. R. M.,
Tate G.,
Boothby M.,
Joanes D. N.,
Davies J. A.,
Roberts B. E.,
Feely M. P.
Publication year - 1990
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1111/j.1365-2141.1990.00122.x-i1
Subject(s) - warfarin , clotting factor , coagulation , factor vii , factor ix , medicine , factor x , vitamin , compliance (psychology) , vitamin k , anticoagulant , gastroenterology , thrombin , platelet , atrial fibrillation , psychology , social psychology
Summary There is a discrepancy in the results of reported studies of levels of vitamin K dependent coagulation factors in patients on warfarin therapy. This may have arisen partly because of the problem of assuring compliance with therapy in outpatients. The plasma concentrations of the vitamin K dependent clotting factors II, VII, IX and X were studied in 23 outpatients whose adherence to prescribed warfarin therapy was determined using a pharmacological indicator of complicance. In these patients, who were shown to have consistently good compliance and stable anticoagulant control over a period of 3–6 months, the activities in plasma of the four coagulation factors were not equally suppressed. Factor IX levels were significantly greater than those of factor VII ( P <0.0001) which in turn were significantly greater than the levels of factor II ( P <0.0001) or factor X ( P <0.0001). There was no significant difference between the levels of factors II and X which were depressed to a similar extent. The proportion of variability of the International Normalized Ratio (INR) explained by linear regression was 51–77% and a model was derived to predict the INR from the mean of the levels of the four clotting factors. The concentrations of the coagulation factors II, VII, IX and X are likely to be highly dependent on the degree of compliance with warfarin therapy which should be taken into account when investigating the behaviour of these factors.