Excessive anticoagulation and anaphylactic reaction after rechallenge with lepirudin in a patient with heparin-induced thrombocytopenia.

Approximately 40% of patients who receive lepirudin for 5-10 days develop antihirudin antibodies. These antibodies lead to decreased renal elimination of lepirudin, ultimately resulting in elevated activated partial thromboplastin times (aPTTs). A small percentage of patients with antihirudin antibodies develop hypersensitivity reactions to lepirudin with reexposure. Thus, patients who are reexposed to lepirudin must be monitored closely for hypersensitivity. A 45-year-old African-American woman received lepirudin for anticoagulation after being diagnosed with heparin-induced thrombocytopenia type II. She developed supratherapeutic aPTTs after 10 days of lepirudin therapy. Lepirudin was then withheld for 6 days, during which her aPTT remained supratherapeutic. After lepirudin infusion was restarted, the patient developed an anaphylactic reaction. She was treated appropriately with an antihistamine, a corticosteroid, and an anxiolytic agent. After the reaction resolved, the patient was rechallenged with lepirudin, and the anaphylactic reaction recurred.