Early prediction of the sensitivity of warfarin in elderly patients by the fall in factor VIIc and protein C at the induction of treatment

Abstract

Indications of oral anticoagulation (OA) therapy for venous thromboembolism and atrial fibrillation increase with age [1]. Elderly patients are more sensitive to OA [2] and their risk for bleeding complications is increased [3,4]. There is a strong relationship between the intensity of the anticoagulant effect and the risk of bleeding [5,6]. A recommendation for an international normalized ratio (INR) of 2.0 to 3.0 is made for most indications [1]. It is important to maintain INR below 3.0 especially in the elderly [7]. Many authors agree that there is a need to improve the safety of anticoagulants in the elderly by careful monitoring of anticoagulant therapy in order to maximize their time in the optimal therapeutic range [1,2,8]. The start of this treatment is a critical period, as the hemorrhagic risk lies mainly in the induction phase [4]. Warfarin is the most widely used oral anticoagulant. It is a drug with a small therapeutic window and its dose–response curve is complex [9,10]. There is a great interand intraindividual pharmacokinetic and pharmacodynamic variability [11]. For all these reasons, it is difficult to predict the correct induction dose [12]. INR is the