Fondaparinux has not been monitored in clinical studies. Therefore, routine coagulation monitoring is not recommended. In patients with moderate renal insuf ciency (ie, CrCl 30-50 mL/min) who require thromboprophylaxis, the dose of fondaparinux should be reduced by 50% or low-dose heparin should be used in place of fondaparinux. Although coagulation monitoring is not recom- mended on a routine basis, there may be circum- stances in which it is useful to determine the anticoagulant activity of fondaparinux. This can be measured using fondaparinux-speci c anti-Xa assays. The therapeutic anti-Xa range for fondaparinux has not been established. However, when given at the 2.5 mg daily dose, the peak steady-state plasma con- centration is, on average, 0.39 to 0.50 mg/L and is reached approximately 3 h post dose. For patients receiving therapeutic doses of fondaparinux (eg, 7.5 mg daily for an individual of average body weight), the mean peak steady-state plasma concentration can be expected to be 1.20 to 1.26 mg/L 3 h post dose. Fondaparinux does not bind to protamine sulfate, the antidote for heparin. 