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Heparin Induced Thrombocytopenia

- Discussion:  (see thrombocytopenia)
    - antibody mediated reaction: PF4–heparin antibodies.  
    - incidence is approximately 3 to 5 percent;
    - mild thrombocytopenia:
           - occurs 2-15 days after initiation of full dose heparin therapy;
           - platlet count usually is > 100,000,  & heparin may be continued;

    - severe immune mediated thrombocytopenia:
           - may occur 7-14 days after low or high dose therapy
           - must d/c therapy-must watch for paradoxical thrombotic conditions;
           - risk of thrombosis remains high for days to weeks after the discontinuation of heparin;
           - risk of thrombosis remains even after the platelet count normalizes;
           - platelet counts rarley drop below 10,000 and rarely cause bleeding;
           - clinical manifestations:
                  - heparin-induced skin necrosis
                  - venous gangrene of the limbs
                  - anaphylactic-type reactions

- Treatment:
    - aspirin is not an adequate therapy for heparin-induced thrombocytopenia;
    - low molecular wt heparing cannot be used because they will cross react;
    - argatroban:
        - small synthetic compound that binds reversibly to the catalytic site of thrombin;
        - combined outcome of death, amputation, and thrombosis at 37 days was significantly lower among those receiving argatroban (34 to 35 percent) than among controls (43 percent);
    - bivalirudin:
          - synthetic thrombin inhibitor that is used during percutaneous coronary intervention;
    - lepirudin / refludane:
          - recombinant form of natual anticoagulant hirudin;
          - specific direct inhibitor of thrombin (independent of antithrombin III)
          - expect highly elevated PTT (even at low dosages) and therefore PTT cannot be used to monitor;
          - IV dose: 0.1 to 0.4 mg/kg
    - coumadin:
          - anticoagulantion is followed by a transition to warfarin, but only after platelet counts normalize;
          - coumadin dosing overlaps w/ direct thrombin inhibitor for at least 5 days and until the INR is therapeutic for at least 48 hours;
          - note that these patients are at risk for coumadin related skin necrosis;
          - coumadin therapy should last at least for one month

Heparin-induced thrombocytopenia. 

Letter - Heparin-Induced Thrombocytopenia.   

Nonheparin Anticoagulants for Heparin-Induced Thrombocytopenia

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