A Retrospective Descriptive Study Evaluating the Incidence of Acute Hypersensitivity Reactions to Crotalidae Immune F(ab')2 (Equine)

Abstract

Specific Aims: To describe the incidence and severity of acute hypersensitivity reactions in patients receiving F(ab’)2 antivenom (Anavip®) for rattlesnake envenomation. Subjects: Adult patients treated with F(ab’)2 antivenom at two community hospitals in Tucson, Arizona Methods: This was a retrospective descriptive evaluation, with data obtained by chart review of all patients who were treated with F(ab’)2 antivenom from April 2019 to August 2020. Patients over the age of 18 years were included. The primary outcome variable was whether an acute hypersensitivity reaction occurred. Main Results: Twenty-three patients were included in the evaluation (mean age = 58.39; SD 12.68; 35% female; 87% white). An acute hypersensitivity reaction was documented in 2 patients (9.0%). No patients received prophylactic medications. Reactions included a rash and urticaria and were considered mild based on study definitions. One of these patients tolerated continuation of the initial F(ab’)2 infusion as well as an additional dose while the other was started on Fab (CroFab®) as an alternative. The average number of F(ab’)2 vials given for treatment was 14.06 (SD 6.19), with 8 patients requiring at least 20 vials total. Conclusions: The incidence of acute hypersensitivity reactions in patients receiving F(ab’)2 antivenom for rattlesnake envenomation was lower than reported in clinical trials. Additionally, all reactions that occurred were mild in nature. Given the small sample size, further studies are needed to determine the true incidence of these reactions.