Prediction of Maintenance Warfarin Dosage from Initial Patient Response

Abstract

This study was conducted to determine the reliability of two methods of predicting maintenance warfarin dosage. Fifty-nine patients were studied using Method 1 and 44 using Method 2. Both methods produced a statistically significant correlation between predicted and actual dose for the two populations. However, actual vs. predicted doses for individual patients were significantly different. Method 1 predicted a dose within +/- 2.5 mg/d of actual dose in only 40.7 percent of patients. With Method 2, the corresponding value was 56.8 percent. Although the linear regression was statistically significant in our population, many patients would have excessive or subtherapeutic dosage predictions.

Assessment of Healthcare Professionals’ Knowledge About Warfarin-Vitamin K Drug-Nutrient Interactions

“…The challenge in warfarin therapy is to obtain stable therapeutic anticoagulation indices which prevent thrombosis and minimize the risk of hemorrhage [16]. Formulas for predicting warfarin-maintenance dose requirements from a patient's initial response to treatment are sometimes employed early in the therapy [17][18][19]. Nonetheless, the predictability of appropriate warfarin dosing remains inadequate and the interaction of diet with the drug is frequently noted as a contributing factor in unstable anticoagulation.…”

Algorithm for Short-Term Prescription of Phenprocoumon

“…However, a prospective investigation [8] on the equations of Williams and Carl [7] and Miller and Brown [3] produced rather poor results, the predicted dose only being correct in 41 and 57% of the patients, re spectively. All these investigations and the present study rely mainly on the close corre lation between the initial effect of anticoagu lation on the prothrombin time and the MD.…”

A model which predicts maintenance warfarin dosage requirements from the response to a single dose [letter]

“…Several methods have been developed, based on correlations found between the prothrombin response to initial doses and the ultimate MD requirement (Routledge et al, 1977;Sawyer, 1983;Williams & Karl, 1979;Fennerty et al, 1984). However, these methods are relatively slow, and take about 3 days before dosage predictions can be drawn; furthermore, the reliability of some of these methods has been questioned (Carter et al, 1983 After discharge from hospital, patients visited the outpatient anticoagulant clinic every 1-2 weeks. The dose which produced a therapeutic and stable (± 0.4) PR on three consecutive visits was defined as the MD.…”