Rattlesnake bite! Reach for the antivenin?

Getty ImagesWhy they did it

Antivenin therapy is commonly recommended to treat dogs with snakebites but is often declined because of its cost. The purpose of this study was to determine what effect, if any, treatment with antivenin for dogs bitten by the prairie rattlesnake (Crotalus viridis) would have on mortality, cost of therapy or duration of hospitalization.

What they did

Researchers evaluated data from 150 dogs presented to a private emergency and referral hospital for envenomation by a prairie rattlesnake between January 2004 and December 2012; 113 of these cases were determined to be eligible for the study. Dogs were divided into two groups: group 1 (n = 31) consisted of dogs that received standard care for envenomation (intravenous crystalloids, pain control, antibiotics); group 2 (n = 82) consisted of dogs that received standard care plus at least one vial of antivenin (antivenin crotalidae polyvalent, or ACP).

Snake envenomation was diagnosed based on “witnessing the snakebite, evidence of bite wounds combined with appropriate clinical signs, or appropriate clinical history and signs combined with the observation of echinocytes on blood smear.” To facilitate comparison between the groups, researchers used a modified snakebite severity score (mSSS) that took into account factors such as the location of the bite, the severity of the swelling and the dog's heart rate and body temperature. There was no statistically significant difference in age, body weight or mSSS between the two groups.

What they found

The median cost of hospitalization for dogs in group 1 was $1,050 (range = $423.52 to $2,266.09), versus a median cost of $2,002.19 (range = $1,139.91 to $6,908.01) among dogs in group 2. With respect to hospitalization, dogs in group 1 were hospitalized for a median of 20 hours (range 8 to 50 hours), while dogs in group 2 were in the hospital for a median of 24 hours (range 1.5 to 74 hours). There was no difference in mortality between the two groups (one dog from each group died).

The authors note limitations in the study such as modifications in the mSSS variables to account for the retrospective nature of the data as well as the subjective nature of some of the information (e.g. assessment of swelling). In addition, there was no detailed follow-up information for most dogs after discharge from the hospital.

The researchers also point out that C. viridis was not one of the crotalidae species used in the creation of the ACP product. While previous studies have implied that cross-reaction from other crotalidae species may still neutralize the venom, whether that is the case with ACP or what dose would be required to be effective is unclear.

Take-home message

There was no significant advantage to using antivenin in dogs envenomated by C. viridis. Dogs treated with antivenin had significantly longer and costlier courses of therapy when compared with dogs treated with supportive care alone. The difference in cost between the two groups was about the cost of the antivenin vial and administration. A prospective, randomized, blinded, controlled clinical trial evaluating the use of ACP in C. viridis envenomation is warranted.

Katzenbach JE, Foy DS. Retrospective evaluation of the effect of antivenom administration on hospitalization duration and treatment cost for dogs envenomated by Crotalus viridis: 113 dogs (2004–2012). J Vet Emerg Crit Care 2015;25(5):655-9.

Click here for link to abstract.