Researchers had access to 115 client-owned dogs who had been bitten by rattlesnakes and whose symptoms associated with the bite were worsening over time. All dogs received “standard supportive care” and one vial of rattlesnake antivenin either given all at once or divided in half with the second dose given six hours after the first. Each dog’s condition was evaluated using a standardized system and assigned a “severity score.”
The scientists found that after receiving the antivenin “the mean severity score of the 115 patients decreased from 4.19 to 3.29 points” and “the mean severity score of the 107 patients without fatalities decreased from 4.16 to 2.15. It didn’t seem to matter whether the dogs received the entire contents of the vial as one dose or divided into two doses.
Giving antivenin is not an entirely benign treatment. Dogs can have adverse (including allergic) reactions to the injection, but in this study only six percent of the dogs had problems associated with the antivenin.
Unfortunately, the evidence supporting the use of antivenin in cats is somewhat questionable. A 2013 study looked at what happened to “115 envenomed cats treated with antivenom* and 177 envenomed cats treated without antivenom” and found:
There was no mortality rate difference between cats that did (6.67%) or did not (5.08%) receive antivenom. A type I hypersensitivity [allergic] reaction was diagnosed in 26 of 115 (22.6%) cats. The use of premedications did not decrease type I hypersensitivity or improve mortality rate. Cats that had a type I hypersensitivity reaction were 10 times as likely to die as were those that did not have such a reaction.