Use of polyvalent equine anti-viper serum to treat delayed coagulopathy due to suspected Sistrurus miliarius streckeri envenomation in two children.

BACKGROUND: Western Pygmy Rattlesnake (WPR) envenomation reportedly causes refractory and persistent coagulopathy when treated with CroFab(®) (Crotalidae Polyvalent Immune Fab). We report two cases where polyvalent equine anti-viper serum (AntivipmynTRI(®)) was used to treat recurrent coagulopathy in children.

CASE DETAILS: The first patient was a 16-month-old male who was bitten by a confirmed WPR. The patient received a total of 18 vials of CroFab(®). His labs normalized, swelling gradually improved, and the child was discharged to home. On day 5, the child returned to the emergency department with a great deal of inguinal tenderness. Labs were obtained and the child's INR was >13.1, while the fibrinogen was <60 mg/dL and the d-dimer was 11.72 mg/L. A decision was made to administer Antivipmyn TRI(®), and the child received a total of 10 vials. Lab values significantly improved: INR 1.2, fibrinogen 93 mg/dL, and d-dimer 4.21 mg/L. The second patient was a 20-month-old male who presented following snake envenomation. The child was administered a total of 22 vials of CroFab(®) over approximately 70 h following envenomation. Physical exam continued to improve, however, lab results showed an increasing INR 1.98, decreasing platelet count 124 × 10(3) per μL, fibrinogen <60 mg/dL, and d-dimer >20 ug/mL. A total of 15 vials of Antivipmyn TRI(®) were administered to this patient. Following this administration, labs and clinical exam both significantly improved. Labs revealed INR 1.16, fibrinogen 110 mg/dL, d-dimer 3.2 mg/L and platelet count 215 × 10(3)/μL.

DISCUSSION: CroFab(®) is still the first-line treatment for children bitten by a WPR, but in some cases patients develop a recurrent coagulopathy. The rapid response demonstrated by Antivipmyn TRI(®) leads us to conclude that this is a potential therapy for this clinical situation.