Hypersensitivity Reaction After Administration of Crotalidae Polyvalent Immune Fab (CroFab).

Crotalidae polyvalent immune Fab (CroFab) is an antivenin that is FDA approved and commonly used to treat envenomations caused by North American pit vipers. Although CroFab has been widely used since the early 2000s, hypersensitivity reactions like type I, type IV, and angioedema have been reported in the literature. We present a case of CroFab induced hypersensitivity reaction in a 41-year-old male shortly after starting CroFab infusion. Furthermore, this patient developed anaphylaxis symptoms including: difficulty breathing, oropharyngeal edema, dysphagia, wheezing, and chest tightness. This was resolved upon stopping CroFab infusion and administering epinephrine, methylprednisolone, diphenhydramine, and famotidine. The reaction occurred again when CroFab was re-introduced despite infusing it at a much slower rate. Interestingly, this patient successfully tolerated crotalidae immune F(ab')2 (equine) antivenom (ANAVIP) upon switching him from CroFab. Hypersensitivity reactions to CroFab can be life-threatening and warrant immediate attention and treatment in a multidisciplinary setting.