A randomized multicenter trial of crotalinae polyvalent immune fab (ovine) antivenom for the treatment for crotaline snakebite in the United States

Background: Current therapy for crotaline snakebite includes antivenin (Crotalidae) polyvalent, an antivenom with numerous adverse effects. We compared the efficacy and safety of 2 dosing regimens with a new antivenom, Crotalinae polyvalent immune Fab (Fab AV). Methods: A single dose of Fab AV alone (as-needed [PRN] group) was compared with an initial dose plus repeated treatments during 18 hours (scheduled group) in a multicenter randomized trial. The study included patients with minimal or moderate envenomation by a crotaline snake within the preceding 6 hours, aged 10 years or older, in whom worsening of the envenomation syndrome was observed before Fab AV treatment. After treatment with Fab AV to achieve initial control, patients were randomized to the scheduled or PRN treatment group. Scheduled group patients received additional doses of Fab AV every 6 hours for 3 doses. The PRN group received no planned additional doses of antivenom. Results: The mean severity score of the 31 patients decreased from 4.35 to 2.39 points (P<.001); there was no difference between scheduled and PRN groups. No patient in the scheduled group received unplanned Fab AV doses, but 8 of 16 patients in the PRN group received unplanned doses (P=.002). Acute reactions occurred in 6 patients (19%), and serum sickness occurred in 6 (23%) of 26 patients who returned for follow-up. Conclusions: In the first randomized trial of antive-nom in the United States, Fab AV effectively terminated venom effects. Since the unplanned use of Fab AV in the PRN group was common, the treatment regimen may require more than 1 initial dose.