- 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