Fondaparinux (Arixtra) is a synthetic pentasaccharide Factor Xa inhibitor. It binds antithrombin and accelerates its inhibition of Factor Xa. Clinically, it is used for the prevention of deep vein thrombosis post-operatively and for the treatment of deep vein thrombosis and pulmonary embolism. Fondaparinux is similar to enoxaparin in reducing the risk of ischemic events, but it substantially reduces major bleeding and improves long-term mortality and morbidity. One potential advantage of Fondaparinux over LMWH or unfractionated heparin is that the risk for heparin-induced thrombocytopenia (HIT) is substantially lower.
In patients undergoing prophylactic treatment with once daily Fondaparinux injections of 2.5mg, the mean peak plasma concentration is 0.39 to 0.50 ug/ml at 3 hours post-dose.
In patients with symptomatic deep vein thrombosis or pulmonary embolism with Fondaparinux injections of 5mg (body weight <50 kg), 7.5mg (body weight 50 to 100kg), and 10mg (body weight >100 kg), the mean peak concentration is 1.20 to 1.26 ug/ml.
These numbers are derived from pharmacokinetic studies completed during Fondaparinux phase III clinical trials.
Clinicians should seek the advice of the on-call Haematologist if they are unsure on how to interpret the anti-XA activity results.
The volume of blood in coagulation samples must lie within the volume range as indicated by the size of the black fill arrow present on tubes. Volumes above or below the arrow will result in sample rejection to ensure validity of results.
Age of sample
Samples will be rejected if received more than 2 hours post venepuncture.
- 2 blue top (sodium citrate) samples
- All coagulation tubes must be adequately filled (see above)
- All coagulation tubes must be mixed several times by gentle inversion immediately after venepuncture. Mixing the sample with the anticoagulant stops the sample clotting within the tube.
- It is not possible to provide results on clotted, insufficient, lipaeamic, or haemolysed samples. These will be rejected with the appropriate comment.
- Samples tubes that have expired cannot be accepted.
Coagulation Lab, James Cook University Hospital, Marton Road, TS4 3BW