CLINICAL OBSERVATIONS, INTERVENTIONS, AND THERAPEUTIC TRIALS Antihirudin antibodies in patients with heparin-induced thrombocytopenia treated with lepirudin: incidence, effects on aPTT, and clinical relevance

Hirudin, a potent and specific thrombin inhibitor, is a protein of nonhuman origin and therefore potentially immunogenic. The primary objectives of this investigation were to determine the incidence of antihirudin antibodies (ahir-ab) in patients with heparininduced thrombocytopenia (HIT) who received lepirudin as parenteral anticoagulation and to determine the incidence of death, limb amputation, new thromboembolic complications (TECs), and major hemorrhage in patients who had ahir-ab, compared with patients who were ahir-ab negative. The investigation used data from 2 prospective multicenter studies with the same study protocol, in which HIT patients received 1 of 4 intravenous lepirudin dosage regimens. The treatment duration was 2 to 10 days.Ahir-ab were determined by a newly developed enzyme-linked immunosorbent assay (ELISA). Eighty-seven of 196 evaluable patients (44.4%) had ahir-ab of the IgG class. Development of ahir-ab was dependent on the duration of treatment (ahir-ab– positive patients 18.6 days vs ahir-ab– negative patients 11.8 days; P 5 .0001). Fewer ahir-ab–positive than ahir-ab–negative patients died (P 5 .001). Ahir-ab did not cause an increase in limb amputation (P 5 .765), new TECs (P > .99), or major bleedings (P 5 .549). In 23 of 51 (45.1%) evaluable patients in whom ahir-ab developed during treatment with lepirudin ( 5 12% of all lepirudin treated patients), the ahir-ab enhanced the anticoagulatory effect of lepirudin.Ahir-ab are frequent in patients treated with lepirudin for more than 5 days. Ahir-ab are the first example for a drug-induced immune response causing enhanced activity of a drug. Therefore, during prolonged treatment with lepirudin, anticoagulatory activity should be monitored daily to avoid bleeding complications. (Blood. 2000;96: 2373-2378)