What are the indications for antivenom use in crotalid envenomations?

Updated: Apr 09, 2021
  • Author: Spencer Greene, MD, MS, FACEP, FACMT, FAAEM; Chief Editor: Joe Alcock, MD, MS  more...
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Answer

Indications for antivenom use include progression of local tissue findings and/or evidence of systemic toxicity (eg, hematotoxicity, airway swelling, cardiovascular collapse). The precise definition of hematologic toxicity is unclear, but many providers use prothrombin time greater than >15 seconds, platelet count less than 150 x 103/µL, or fibrinogen level less than 220 mg/dL, or a significant change from baseline, as indications to treat. It should be emphasized that the SSS should not be used to determine the need for treatment. Reliance on this scale can result in significant undertreatment.

If the swelling and tenderness are more than minimal and have extended beyond a major joint (eg, wrist, ankle), antivenom is warranted. [42] If there is significant local tissue injury (eg, necrosis), antivenom is also indicated, even if the swelling has not progressed across a joint. A randomized clinical trial studying the effects of FabAV on copperhead bites demonstrated that even mild bites recovered better when treated with antivenom. [59] Specifically, patients had improved limb function at 7, 10, and 14 days post envenomation compared with the placebo group, and 75% of treated patients had full recovery of limb use by day 31, whereas the control group did reach this milestone until 57 days. Treatment was especially beneficial in patients who were treated within 5.5 hours of envenomation. [60] Additionally, people who were treated with antivenom required opioids for a much shorter duration. [61]

The decision to use one over the other will likely be based on several variables, including availability, cost, and safety concerns, such as prior sensitization to equine- or ovine-derived products.

Epinephrine is useful in patients with anaphylaxis, and diphenhydramine can help with mild urticaria and pruritus, but neither is a substitute for antivenom.


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