The clinically most important negative properties of coumarin anticoagulants are their numerous interactions with other drugs. Data in the literature on these interactions are frequently controversial. The causes of this phenomenon are a) the complicated path from ingestion of anticoagulants to their clinical effect and laboratory results, b) interindividual differences in enzyme activity participating in vitamin K metabolism, in the synthesis of hemocoagulation factors and in the biotransformation of coumarin derivatives, c) the different clinical state of the patient on the one hand and the healthy volunteer on the other, d) differences in the biotransformation of different coumarin derivatives and their optic isomers. In the submitted paper the authors describe pharmacokinetic and pharmacodynamic mechanisms of drug interactions of coumarin anticoagulants and their importance for clinical practice. In the conclusion recommendations are submitted to reduce the risk of these interactions.

Keywords: Anticoagulants /adverse effects/; Coumarins /adverse effects/; Drug Interactions; Humans