Evaluation of a computer-assisted method for individualized anticoagulation: retrospective and prospective studies with a pharmacodynamic model.

We studied the effectiveness of a computer program based on a mathematic model of warfarin dynamics in assisting with the initial phases of anticoagulation. In retrospective evaluations the program was successful in predicting prothrombin complex activity (PCA) responses for three different groups of subjects, indicating that the model is a good representation of the physiologic system. In a prospective evaluation of the program a computer-assisted group of 10 patients was compared with a control of 10 patients who did not receive computer assistance. Because of the program's very conservative upper limits for warfarin dosage in the first few days of therapy, the computer-assisted patient require slightly more time (6 days), on the average, to first reach PCA values in the 20% to 30% therapeutic range than did the control patients (4.8 days). After the desired PCA had been achieved, however, the computer-assisted group remained within the therapeutic range for 83% of the time compared to only 60% for the control group. This difference was due primarily to much less overanticoagulation of the computer-assisted patients than of the controls.