A Case Report of Crotalidae Immune F(ab')-associated Coagulopathy Recurrence in a Preschool-age Child.

Introduction: Pit viper envenomation may cause coagulopathy. The coagulopathy has been treated with crotalidae polyvalent immune fragment antigen-binding (Fab) ovine antivenom for the last few decades in the United States and usually corrects the acute coagulopathy within hours. Days after receiving Fab, coagulopathy may recur in approximately half of the patients. Another divalent antivenom, crotalidae immune F(ab') (equine)-F(ab')-was approved by the US Food and Drug Administration for the treatment of pit viper envenomation. F(ab') is composed of two linked antigen-binding fragments of immunoglobulin G. Several studies have demonstrated that F(ab') is less likely to be associated with recurrence. There is no reported case of F(ab')-associated late coagulopathy in very young patients. We report the first case of recurrence associated with F(ab') use in a preschool-age child.

Case Report: A preschool-age male developed leg swelling and hypofibrinogenemia after rattlesnake envenomation. F(ab') was administered to stabilize the leg edema and to correct the hypofibrinogenemia. The patient improved clinically and was discharged on hospital day five. Seven days after the rattlesnake envenomation, he returned to the emergency department as instructed. Laboratory data revealed recurrent hypofibrinogenemia.

Conclusion: There are two antivenoms available in the US to treat crotalid envenomation, Fab and F(ab'). F(ab') is less likely to be associated with recurrent coagulopathy in comparison to Fab. We report the first case of recurrence associated with F(ab') in a preschool-age child. It is important that the emergency physician be aware of potential F(ab')-associated recurrent coagulopathy. Adult and pediatric patients may need to follow up to be evaluated for hypofibrinogenemia and/or thrombocytopenia after receiving F(ab').