Appraisal of current vitamin K dosing algorithms for the reversal of over-anticoagulation with warfarin: the need for a more tailored dosing regimen.

Warfarin is the most commonly prescribed oral anticoagulant in the UK for the treatment and prevention of thromboembolic disorders. Vitamin K administration is an effective way of reversing excessive anticoagulation. Over-anticoagulated patients present with a wide range of international normalized ratio (INR) values and may respond differently to a fixed dose of vitamin K. Current dosing algorithms for vitamin K administration in the non-urgent treatment of over-anticoagulation do not take this variability in response into account. Consequently, over a third of over-anticoagulated patients still remain outside their target INR 24 h after treatment. Such patients are therefore prone to either haemorrhage (if the patient is still over-anticoagulated) or thromboembolism (if the INR reversal is over-corrected). A number of factors such as patient age, body weight, co-morbidity, frailty, warfarin daily dose and CYP2C9 and VKORC1 polymorphism could affect response to vitamin K and thus the rate and extent of INR reversal. There is a need for a more individualized approach to the reversal of over-anticoagulation in asymptomatic or mildly haemorrhagic patients in order to improve the safety of warfarin therapy.