Although the quality of oral anticoagulant treatment is already high, improvement is important. We performed several studies which all aimed to optimize dosing of vitamin K antagonists and control... Show moreAlthough the quality of oral anticoagulant treatment is already high, improvement is important. We performed several studies which all aimed to optimize dosing of vitamin K antagonists and control of anticoagulant treatment. In our double-blind controlled trial comparing a simple dosing algorithm to an algorithm that incorporated the patients__ sensitivity for vitamin K antagonists, we showed that there was no increase in treatment quality. However, the new algorithm was more efficient, as more dosage proposals were generated and accepted. We studied the relationships between maintenance dosages between acenocoumarol, warfarin and phenprocoumon and calculated transition factors. In a prospective cohort study among 220 Italians initiating anticoagulant treatment with acenocoumarol we showed that CYP2C9*3 was associated with a 25% dose-reduction and an increased risk of over-anticoagulation (INR>6) on day 4. Two copies of the VKORC1*2 alleles were associated with a 45% dose-reduction and an increased risk of over-anticoagulation. Instability is a risk factor for developing complications. We studied several methods to reflect instability and investigated which method was best associated with complications. We also investigated determinants of instability. Finally, we present the design and general results of a trial with primary aim to compare the quality of treatment with warfarin to phenprocoumon. Show less