[Monitoring anticoagulation by fondaparinux: determination of anti factor Xa-level].

In contrast to low molecular weight heparin and unfractionated heparin fondaparinux is a selective synthetic factor Xa inhibitor. It was approved for thromboprophylaxis after major orthopaedic surgery three years ago. Because of its excellent bioavailability after subcutaneous application once daily independent of body weight (within the range of 50-100 kg) monitoring of the substance is usually not necessary. Since its recent approval for therapeutic use in acute venous thrombosis monitoring might be useful in special clinical situations (e. g. suspected over- or underdosing, renal insufficiency or severe bleeding complications). Based on standard laboratory methods for the chromogenic determination of the anti-factor Xa activity of low molecular weight heparin several chromogenic substrate assays were published for monitoring. Only fondaparinux should be used for calibration and measured fondaparinux levels should be expressed in mug/ml of the fondaparinux calibrator. Because of its single synthetic chemical entity, a linear dose/response relationship over a wide concentration range is observed and measurements are of high precision.