Travel and Oral Anticoagulation

Millions of individuals worldwide are on permanent or temporary oral anticoagulation treatment with vitamin K antagonists (VKAs). The effectiveness of VKAs has been established by clinical trials for several indications. Among these, the primary or secondary prevention of venous thromboembolism, the prevention of systemic embolism in patients with prosthetic heart valves, or atrial fibrillation are of highest relevance.1 Such travelers are at higher risk for bleeding episodes due to the anticoagulation and for thromboembolic events due to the underlying disease. This article reviews the most important issues to be considered to give adequate advice to travelers on oral anticoagulants. Vitamin K is an essential cofactor for the production of functional clotting factors II, VII, IX, and X, as well as inhibitors such as protein C, S, and Z.2 If vitamin K is deficient or the effect of vitamin K is pharmaceutically blocked, the above‐mentioned clotting factors cannot be activated, and the dependant clotting time is prolonged. The three available VKAs phenprocoumon, warfarin, and acenocoumarol exert their anticoagulant effect by reducing the regeneration of vitamin K from vitamin K epoxide in the vitamin K cycle.3 The main difference between the different VKAs is the different half‐life with the 105 to 114 hours for phenprocoumon, 35 to 45 hours for warfarin, and 9 hours for acenocoumarol. Several exogenous and endogenous factors influencing the metabolism of vitamin K and its antagonists (eg, nutrition, comedication, antibiotics) result in individual response to the treatment. ### The International Normalized Ratio and Patient Self‐Management The small therapeutic range of the oral anticoagulant drugs and the potentially life‐threatening effects of both underdosing and overdosing necessitate a close control of the actual intensity of anticoagulation using the international normalized ratio (INR).4 A major improvement toward an increased mobility of patients permanently treated with VKAs was the introduction of self‐testing and self‐dosing of the … Corresponding Author: Jurgen Ringwald, MD, Department of Transfusion Medicine and Hemostaseology, University Hospital of Erlangen, Krankenhausstrase 12, D‐91054 Erlangen, Germany. E‐mail: juergen.ringwald{at}ukerlangen.de