Heparin Induced Thrombocytopenia Clinical Review
Internal Medicine Based Clinical Pharmacy Review
Heparin Induced Thrombocytopenia is a complication that results from heparin therapy. Clinical manifestation in patients results in an increased likelihood to clot.
In addition to Heparin, other drugs may also initiate a similar response and may include:
2 Major Types
Type 1 (non-immune mediated): Immediate thrombocytopenia (within 48 hours) but normalization of platelets occurs over duration of heparin treatment
Type 2 (immune mediated): Presents between 4–10 days of heparin therapy and is considered life threatening with no intervention
Distinguishing features includes platelets dropping below 150K or 50% reduction in platelets from baseline (even if total platelets remain >150K).
Severe complication with HIT may result in conversion to Heparin Induced Thrombocytopenia + Thrombosis (HITT). This conversion is rare and occurs in around ¼ of patients of all patients how experience HIT.
Antibodies produced by the immune system binds to heparin and platelet factor 4 (PF4). Formed complex causes platelet activation, release of pro-coagulant particles, platelet consumption, and ultimately thrombocytopenia.
How To Treat
- Discontinue heparin ASAP!
- Initiate alternative anticoagulant therapies
- FDA Approved: Argatroban (Preferred Therapy)
- Non-FDA Approved: Bivalirudin or Fondaparinux
- Transition to Warfarin once platelets have recovered and patient is clinically stable
Key Clinical Pearls
If patients are positive for renal dysfunction: Argatroban is preferred.
If patients are positive for hepatic dysfunction: Bivalirudin (or dose adjusted Argatroban) is preferred.
If undergoing cardiac surgery: Bivalirudin is preferred.
If patient is pregnant: Fondaparinux is preferred.
Platelets are preferred to be > 150K (although many institutions have different protocols and varying cut offs so don’t take this value to literally).
Bridge warfarin with Argatroban x 5 days ensuring INR is therapeutic (INR>4) for a minimum of 24 hours.
Warfarin duration with HIT: no less than 1 month
Warfarin duration with HITT: no less than 3 months
After discontinuation of heparin, average time for platelets to recover levels >150K is typically 4 days.
In severe cases, can take up to 2 weeks.
Summary of Key Clinical Points
Although predominantly associated with heparin, thrombocytopenia may also occur with other drugs such as vancomycin or lorazepam.
Platelets dropping to less than 150K or a sudden 50% reduction of platelets is the distinguishing sign of HIT.
First line alternative upon discontinuing heparin is argatroban.
5 days of argatroban x warfarin bridge is important to prevent microvascular clots.
Which of the following statements is correct?
- Most patients present with HITT as oppose to HIT
- Bridging for 2 days with argatroban and warfarin is needed to prevent microvascular clots
- Fondaparinux is preferred in female HIT patients who may also be pregnant
- There is no risk of thrombocytopenia with any other drugs other than heparin
- Konkle BA. Disorders of Platelets and Vessel Wall. In: Kasper D, Fauci A, Hauser S, Longo D, Jameson J, Loscalzo J. eds. Harrison’s Principles of Internal Medicine, 19e. New York, NY: McGraw-Hill; 2015. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1130&Sectionid=79732426. Accessed October 24, 2016.
- Hematologist. Heparin-Induced Thrombocytopenia being Treated with Argatroban with Persistent Thrombocytopenia. http://www.hematology.org/Thehematologist/Ask/1187.aspx. Accessed October 24, 2016.
- Medscape. Heparin-Induced Thrombocytopenia. http://emedicine.medscape.com/article/1357846-overview#showall. Accessed October 24, 2016.