Predicting the Optimal Maintenance Dose of Warfarin (Marevan) Based on Multiple Influential Factors

Abstract

Abstract Introduction Although there are new anticoagulant drugs, warfarin is useful after surgery. The safety margin of warfarin is narrow, requiring precise dosing to avoid unpredicted bleeding and thrombophilia/embolisms. The initial dose is adjusted depending on the prothrombin time–international normalized ratio (PT-INR) level to establish the maintenance dose. The monitored adjustment may take several days. Objective To formulate a valid and reliable equation that indicates the daily maintenance dose of warfarin “Marevan” to achieve closest PT-INR levels to the targets. Methods Studies were conducted on 150 adult patients treated with daily doses of warfarin “Marevan” for different therapeutic/prophylactic indications with variable PT-INR results (1.15-12.7). The samples were drawn at least 2 days after the drug initial administration. Laboratory tests were analyzed using fully automated machines with reviewed quality control and preanalytical precautions. A continuous multiple regression analysis was undertaken. The dependent variable was the daily warfarin “Marevan” dose in milligrams. The independent variables included PT-INR, serum albumin concentration, patient age, hematocrit, height, weight, and estimated total plasma albumin amount. A review of the clinical history and disease category was undertaken and paired with the findings to validate and discover the equation’s limitations. Results Multiple regression analysis revealed significant results (multiple r > 0.8 with minimal two-sided P values). A reliable equation was developed to predict the warfarin “Marevan” dose, which mostly achieves a PT-INR level of 3.0 or any targeted level. The equation encompassed almost two-thirds of all potential variables, including the effect of other drugs’ interaction. Clinically, the equation was applicable to cases with coexisting lupus thrombophilia, severe anemia, or renal or liver diseases. In the presence of moderate or severe cold agglutinins, the equation predicted underestimated doses. Conclusion Predicted warfarin “Marevan” dose = + 45.9505 + (0.770598 × PT.INR) – (5.67861 × Serum.Albumin.Concentration) – (0.0933151 × Patient.Age.In.Years) + (0.507168 × Hematocrit) – (0.296932 × Height.In.Centimeters) – (0.21711 × Weight.In.Kilograms) + (0.290377 × Estimated.Total.Plasma.Albumin.Amount).