Acute Hypersensitivity Reactions Associated With Administration of Crotalidae Polyvalent Immune Fab Antivenom

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Acute hypersensitivity reactions are well known to occur with the administration of the Antivenin (Crotalidae) Polyvalent (Wyeth Laboratories, Marietta, PA). Crotalidae polyvalent immune Fab (ovine) (CroFab; FabAV, Protherics, Inc., Brentwood, TN) was introduced in 2001, and early studies reported a hypersensitivity reaction rate up to 19%. We describe the incidence of acute hypersensitivity reactions to FabAV in patients bitten by rattlesnakes. This was a nonconcurrent observational cohort study, with data obtained by chart review of all patients admitted to our service for rattlesnake bites from July 2000 to June 2004. The study was conducted at an urban Level I trauma center and urban children's hospital. All patients treated with FabAV were included. Those who received no antivenom or who were treated with Antivenin (Crotalidae) Polyvalent were excluded. The main outcome variable was whether an acute hypersensitivity reaction developed. Ninety-three patients were included in the review (72 male and 21 female patients). The mean age was 34.5 years (range 16 months to 91 years), and the mean dose of antivenom was 12 vials (range 4 to 32 vials). The incidence of acute hypersensitivity reactions was 5 of 93, or 5.4%. Four patients developed a mild reaction that was easily treated and were able to finish the full course of antivenom. Only 1 patient developed a reaction that prevented further antivenom administration. FabAV appears to be associated with a lower incidence of acute hypersensitivity than initially reported. Most reactions are mild and easily treated and do not preclude further dosing of antivenom.