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Heparin-induced thrombocytopenia (HIT)
Heparin-induced thrombocytopenia (HIT) is the development of thrombocytopenia
(low platelet counts) due to the administration of heparin, either in its "unfractionated"
or "low molecular weight" form. HIT may affect up to 3% of patients
exposed to heparin. HIT is very rare in patients treated with low
molecular weight heparin (LMWH). More than half of the patients with
asymptomatic HIT may experience formation of abnormal blood clots
in the following 30 days.
There are two types of
Type I occurs within a few days of heparin exposure. Self limited and benign.
Type II occurs from 5 days to 3 weeks after starting treatment. Autoimmune
immunoglobulin-mediated syndrome associated with venous and arterial thrombosis.
Although the diagnosis of HIT is made
primarily on clinical grounds laboratory tests such as the heparin/PF
4 ELISA, heparin-induced platelet aggregation (HIPA), and the serotonin
release assay (SRA) are used to help confirm the diagnosis.
The Pregnancy and Thrombosis Working Group recommends that if the platelet count drops below 150,000 or 50% from baseline during heparin or LMWH
therapy, it is recommended to stop heparin
including IV flushes. It is recommended that patients diagnosed with HIT should
have consultation with a hematologist and be treated with fondaparinux .
sodium (Arixtra ®)
Synthetic and specific inhibitor of activated Factor Xa.
Molecular weight = 1728
- Prophylaxis (no active clot)
2.5 mg subcutaneous injection once daily
- Therapeutic (active thrombosis) 
Less than 50 kg
5 mg subcutaneous injection once daily
50 to 100 kg
7.5 mg subcutaneous injection once daily
Greater than 100 kg
10 mg subcutaneous injection once daily
ARIXTRA Injection is contraindicated in patients with severe
renal impairment (creatinine clearance < 30 mL/min), active major bleeding,
bacterial endocarditis, in patients with thrombocytopenia associated with a
positive in vitro test for anti-platelet antibody in the presence of
fondaparinux sodium, or in patients with known hypersensitivity to fondaparinux
When epidural/spinal anesthesia or spinal puncture is employed, patients
anticoagulated or scheduled to be anticoagulated with low—molecular-weight
heparins, heparinoids or fondaparinux sodium are at risk of developing an
epidural or spinal hematoma, which can result in long-term or permanent
(2.5 mg, 5mg, 7.5 mg, 10 mg single dose prefilled syringes)
Fondaparinux has been reported to cross over to the fetus in small
amounts. Although the dose appears to be below the concentration that effectively thins the blood potentially
hazardous effect cannot be ruled out. The authors of this report suggested
that the use of Axitra in pregnant women "might best be limited to those for
whom there are no obvious therapeutic alternatives, such as patients with
heparin induced thrombocytopenia or severe allergic reactions to heparin ".
Fondaparinux sodium was found to be excreted in the milk of
lactating rats. However, it is not known whether this drug is excreted in
1. Duhl AJ et. al Antithrombotic therapy and pregnancy: consensus report and recommendations for the prevention of venous
thromboembolism and adverse pregnancy outcome. Am J Obstet Gynecol
Dempfle CE. Minor transplacental passage of fondaparinux in vivo. N Engl J
Med. 2004 Apr 29;350(18):1914-5.