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A randomized multicenter trial of Crotalidae polyvalent immune Fab antivenom for the treatment of rattlesnake envenomation in dogs


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Dr. Michael E. Peterson, Reid Veterinary Hospital, 933 SW Queen Ave, Albany, OR 97321, USA. Email:


Objective – To determine clinical efficacy of the Crotalidae polyvalent immune Fab (ovine) antivenom (OPCA) against progressive crotalid envenomation in the dog as reflected in stabilization or improvement of snakebite severity scores (SSS). Additionally, due to the potential decreased half-life of the Fab antibodies in dogs we compared SSS between dogs receiving 2 different dosing regimes.

Design – Prospective, clinical trial.

Setting – Five veterinary emergency and critical care facilities.

Animals – One hundred and fifteen client-owned Crotalid (rattlesnake) snake bitten dogs in whom worsening of the envenomation syndrome was observed before OPCA treatment.

Interventions – In a multicenter randomized clinical trial a single dose (1 vial) of OPCA alone was compared with 2 doses (1/2 vial each) administered 6 hours apart. Standard supportive care was provided in all cases.

Measurements and Main Results – Data were available for 115 patients, 9 of which were fatalities. All patients' clinical condition was documented with a standardized SSS system accounting for each major body system. Each fatality received maximum severity scores of 20. The mean severity score of the 115 patients decreased from 4.19 to 3.29 points and there was no difference between the 2 treatment groups. The mean severity score of the 107 patients without fatalities decreased from 4.16 to 2.15. Antivenin-related acute reactions occurred in 6 dogs (6%), and no serum sickness occurred within the 95 cases contacted at the 2-week posttreatment follow-up.

Conclusions – In the first randomized trial in dogs of antivenin in the United States, OPCA effectively stabilized or terminated venom effects. There were no statistical differences detected between treatment groups within the study time frame.