(914) Comparison of F(ab’)2 Versus Fab Antivenom in North American Pit Viper Envenomation

Introduction: There are only two antivenoms on the market approved to treat North American pit viper envenomation; crotalidae polyvalent immune Fab (ovine) and crotalidae immune F(ab’)2 (equine). Current standard of care is to treat with whichever antivenom is available at the institution as soon as possible, but there is no consensus on which agent may be more effective. This study aimed to compare the efficacy and safety outcomes for patients envenomated by a North American pit viper who received either of these antivenoms.

Methods: Subjects were divided into Fab or F(ab’)2 groups based on which antivenom they received upon arrival to the emergency department. All patients two years of age and older were included if they received either agent. F(ab’)2 and Fab patients were collected from July 2019 to December 2022 and January 2016 to July 2019, respectively. The primary outcome compared the amount of Fab or F(ab’)2 doses needed to achieve initial control. Secondary outcomes included incidence of recurrent coagulopathies, skin and soft tissue injury, 30-day readmission, hospital length of stay, cost of drug therapy, and adverse events (serious and non-serious).

Results: A total of 114 patients were included, 57 in each group. F(ab’)2 patients had a higher incidence of hematologic symptoms (29 vs. 43, p = 0.007) and lower fibrinogen levels (273 vs. 293, p = 0.007) at baseline. F(ab’)2 patients required less doses to achieve initial control compared with the Fab group (1 vs. 4 doses; 95% CI [2.318, 3.282]; p < 0.001), had a shorter length of stay (36 vs. 46 hours, p = 0.001), and lower cost of drug therapy ($12,200 vs. $36,000, p < 0.001). There were no differences between groups in recurrent coagulopathies [20 (F(ab’)2) vs. 13 (Fab), p = 0.148), serious adverse events [1 (F(ab’)2) vs. 0 (Fab); p = 0.315] and readmission within 30 days [1 (F(ab’)2) vs. 0 (Fab); p = 0.315]. The incidence of non-serious adverse events was greater in the F(ab’)2 group (10 vs. 1 event; p < 0.001).

Conclusions: Patients treated with F(ab’)2 antivenom for North American pit viper envenomation required less doses to achieve initial control, had a shorter hospital length of stay, and reduced drug cost compared to patients who received Fab antivenom, but experienced a greater incidence of non-serious adverse events.