Drug-induced thrombocytopenia after SARS CoV-2 monoclonal antibody administration treated with plasma exchange

A number of different therapeutic modalities have been tried for SARS CoV-2 infection, including monoclonal antibodies against the spike protein such as imdevimab/casirivimab (REGEN-COV). We report a case of severe thrombocytopenia due to REGEN-COV that was treated successfully with a course of plasma exchange. An 84 y M who lived alone was hospitalized with fatigue and dyspnea, and hematuria. He had a history of atrial fibrillation for which he was taking rivaroxaban. On admission he was mildly anemic with normal platelets. Testing was positive for SARS C0V-2 by PCR. The rivaroxaban was discontinued and a cystoscopy showed two bleeding sites which were treated by cauterization. He received REGEN-COV, and over the next two days his platelet count dropped from 153 to < 1 × 10⁹/L. A diagnosis of drug-induced thrombocytopenia due to REGEN-COV was made and despite platelet transfusions, intravenous immunoglobulin 2 g/kg, and dexamethasone 40 mg daily, his platelet count stayed at < 1 or 1 × 10⁹/L. Since REGEN-COV has a half-life of three weeks or more, plasma exchange was considered as a means of removing the drug. Plasma exchange daily, with plasma replacement was started on the ninth hospital day and continued for four days. The platelet count sequentially increased daily and was within the normal range by day 14. The hematuria cleared by day 11. The patient was treated for SARS-CoV-2 by other means and discharged on day 22. Plasma exchange should be considered when rapid removal of therapeutic monoclonal antibody is warranted due to life-threatening side effects.