Improvement in the regulation of the vitamin K antagonist acenocoumarol after a standard initial dose regimen: prospective validation of a prescription model

Background In a retrospective study we have developed a model which determines the dose of acenocoumarol based on the age of the patient and on the first INR obtained after a standard initial loading dose. The group of patients of this study was used as the control group of the present study. Aim The aim of this study was to prospectively validate the model and to assess whether the use of this model improves the quality of the treatment in the 0-2 months study period. Patients and methods In 197 patients the model was evaluated by (1) in the initial phase: comparison of INRs with the control group, after assessing the dose according to the model, and (2) in the 0-2 months period: calculation of the percentage of time spent in the therapeutic target range compared to the control group. Furthermore, the eventual dose was compared to the dose of the model when the INRs were within the therapeutic target range for the first time and on two successive occasions. Results (1) When dosed according to the model, 50% of INRs in the total group were within the therapeutic target range compared to 45% in the control group, and (2) the percentage time spent within this range was 68 in the total group compared to 63 in the control group (P = 0.0013). When the INRs were within the range for the first time and successively twice, the eventual doses were similar to the model in 59 and 50%, respectively. About 20% of the patients did not achieve two successive INRs within the range. Conclusions Using the model the quality of treatment improved. We advice to use a standardized individualized dose regimen at the initiation of vitamin K antagonist treatment.