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Scheduled or PRN Crofab for Rattlesnake Bites?

August 6, 2018

Written by Alex Chen, MD

Spoon Feed
PRN dosing of antivenom (Crofab) for rattlesnake bite based on a clinical and laboratory-triggered strategy led to an overall decreased hospital length of stay (LOS) (27h vs 34h) and amount of antivenom used (8 vs 16 vials) compared to standard maintenance dosing.

Why does this matter?
Rattlesnake envenomations can lead to significant morbidity from local tissue ischemia and hemotoxicity. Our mainstay of treatment is antivenom (Crofab); however, this comes at significant cost due to the price of Crofab (~$2300 per vial, not including hospital mark-up) and the fact that it often requires initial ICU monitoring for anaphylaxis and frequent neurovascular checks. The current manufacturer guidelines recommend maintenance dosing of antivenom after the initial bolus dose. If you are in a rattlesnake endemic area, these costs can add up quickly for healthcare systems and most importantly, the patient.

“Set it and forget it”?
This was a retrospective cohort study of 310 adult rattlesnake envenomations at a regional toxicology center in Phoenix, AZ from 2007-2014. Prior to 2011, it was routine practice for maintenance dosing of antivenom (2 vials q6h x 18h). Beginning in 2011, PRN dosing was initiated based on clinical and laboratory triggers. Primary outcomes were hospital LOS and total vials of antivenom used. Secondary outcomes included readmission, retreatment, bleeding, surgery, and hemotoxicity (defined as platelets <120 k/mm3 or fibrinogen <170 mg/dl)

The PRN group required fewer vials of Crofab in total (8, IQR 6-12) compared to the maintenance group (16, IQR 12-18). The PRN group also had a shorter length of hospital stay (27h, IQR 20-14). In terms of secondary outcomes, there were no statistically significant differences at 60 days. This study did not look at follow-up lab values. There is some evidence that maintenance dosing can reduce late hemotoxicity, but this did not seem to lead to a difference in patient-centered outcomes in this study.

Ultimately, this study provides data that having someone with experience in managing rattlesnake envenomations (usually a medical toxicologist) can create significant cost savings for a healthcare system and the patient, with similar outcomes.

Comparison of Antivenom Dosing Strategies for Rattlesnake Envenomation.  Crit Care Med. 2018 Jun;46(6):e540-e544. doi: 10.1097/CCM.0000000000003079.
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Reviewed by Clay Smith

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