HYPERSENSITIVITY AND RESISTANCE TO ORAL A NTICOAGULANTS

During the initial phase or during treatment with oral anticoagulants, hypersensitivity or resistance may be observed, requiering significan t changes in prescribed dosage. A thorough knowledge of the mode of ac tion of vitamin K and its antagonists is useful to improve understandi ng of unexpected response to oral anticoagulant therapy. These abnorma l responses may be due to poor compliance to treatment by the patient, insufficient or excessive vitamin K intake, interference with other d rugs or abnormalities of the hepatic enzymes which are the target of o ral anticoagulant drugs. The search for a cause is justified by the ri sks associated with these abnormal responses. It must be rigorously un dertaken with an accurate interrogation, use of an anticoagulation mon itoring leaflet and, if necessary, measurement of plasma concentration s and pharmacokinetics of the anticoagulant drug.