Factors Associated With Difficulty Achieving Initial Control With Crotalidae Polyvalent Immune Fab Antivenom in Snakebite Patients


  • Presented at the 2009 North American Congress of Clinical Toxicology meeting, San Antonio, TX, September 2009.

  • This study was a secondary analysis of data that were originally collected in a study funded by a grant from Fougera (now Nycomed, Zurich, Switzerland). Rocky Mountain Poison and Drug Center also received grant funding to revalidate and reanalyze the data from Protherics (now BTG, West Conshohocken, PA). Rocky Mountain Poison and Drug Center has consultation and call center contracts with Nycomed and BTG. The authors are salaried employees of Rocky Mountain Poison and Drug Center and do not receive any direct funding from Nycomed or BTG.

  • Supervising Editor: Mark Mycyck, MD.

Address for correspondence and reprints: Shan Yin, MD, MPH; e-mail: shan1yin@gmail.com.


ACADEMIC EMERGENCY MEDICINE 2011; 18:46–52 © 2011 by the Society for Academic Emergency Medicine


Background:  The prescribing information for Crotalidae Fab antivenom (FabAV) instructs clinicians to administer FabAV until initial control of the envenomation syndrome is achieved. Risk factors for difficulty achieving initial control are not known.

Objectives:  The study aim was to identify factors present before administration of antivenom associated with difficulty achieving initial control.

Methods:  The authors conducted a retrospective study of all patients presenting to any one of 17 centers and receiving FabAV from 2002 to 2004. Demographic and historical information, as well as data about nine specific venom effects, were collected prior to the administration of antivenom. An expert panel used standard criteria to determine if initial control was achieved. The patient group that had difficulty achieving initial control was compared to the group that achieved initial control, and adjusted odds ratios were calculated using stepwise logistic regression.

Results:  A total of 247 patients were included in the final analysis. The majority of patients were envenomated on the upper extremity and were young males. A total of 203 patients (82.2%) achieved initial control. In univariate analysis, thrombocytopenia, bleeding, neurologic effects, and a severe bite were significantly associated with difficulty achieving initial control. After logistic regression, the presence of neurologic effects and thrombocytopenia remained significantly associated with difficulty achieving initial control. When both factors were present, the patient was 13.8 times more likely to have difficulty achieving initial control.

Conclusions:  A number of factors were present before the administration of FabAV that were independently associated with difficulty achieving initial control of the envenomation syndrome. Predicting which patients will have difficulty achieving initial control has important ramifications for patient disposition and may provide insight into the mechanisms for lack of antivenom efficacy.