The effect of the plasma levels of proteins C and S on the prediction of warfarin maintenance dose requirements.
OBJECTIVE
Determination of the effects of the vitamin K-dependent anticoagulants, proteins C and S, on warfarin dose requirements and on the prediction error of a bayesian warfarin dose predicting program.


METHODS
Patients in the study were consecutive inpatients (n = 18) starting treatment with warfarin who were monitored as outpatients for 4 weeks. The following measurements were taken: repeated (n = 8) prothrombin times, expressed as the international normalized ratio (INR), plasma protein C and S antigen levels (percentage of pooled normal plasma), demographic, clinical and biochemical variables.


RESULTS
Maintenance doses (adjusted to INR 2.5) were 6.7 +/- 3.4 mg/day. Protein C decreased to 56.9% +/- 15.3%, protein S to 63.7% +/- 17.3%, INR increased to 2.46 +/- 0.14. Prediction error decreased from 2.84 +/- 2.0 mg/day to 0.95 +/- 0.78 mg/day. Protein C accounted for only 4.2% of the mean maintenance dose but protein C and S levels accounted for 31% of the mean dose prediction error.


CONCLUSIONS
Protein C and S levels affect warfarin doses and predictions significantly but not to a clinically meaningful degree.
Lubetsky
A
A
Department of Medicine A, Sheba Medical Center, Tel Hashomer, Israel.
Seligsohn
U
U
Ezra
D
D
Halkin
H
H
D000293:Adolescent; D000328:Adult; D000368:Aged; D001499:Bayes Theorem; D001835:Body Weight; D016903:Drug Monitoring; D005260:Female; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011486:Protein C / Q000032:analysis*; D017293:Protein S; D011517:Prothrombin Time; D012984:Software; D014859:Warfarin / Q000008:administration & dosage* / Q000627:therapeutic use
D006023:Glycoproteins; D011486:Protein C; D017293:Protein S; D014859:Warfarin