Hematologic Abnormalities Following Crotaline Snakebites In South Carolina

Pit viper envenomation causes local tissue edema, pain, and ecchymosis. In certain geographical areas of the United States thrombocytopenia, hypofibrinogenemia and coagulopathy are common hematological abnormalities, and ones that dictate both a reason for treatment with antivenom as well as an important monitor of therapeutic efficacy. Data on the frequency and severity of hematological abnormalities following envenomation by crotaline species in South Carolina has not been reported. We evaluated clinical and hematologic laboratory findings and treatment course following copperhead and rattlesnake bites in South Carolina.

We conducted a retrospective evaluation of all copperhead and rattlesnake bites reported to the Palmetto Poison Center from April 2005 through June 2010. Severity of the snakebite and development of hematologic toxicity associated with envenomation cases were documented before and after crotaline Fab antivenom (CroFab®) administration. Adverse events associated with antivenom therapy, recurrence phenomena, delayed onset of symptoms, and performance of fasciotomy were also recorded.

Overall, 194 crotaline snakebites were identified- 156 copperhead bites and 38 rattlesnake bites. Males accounted for 75% of copperhead bite patients (median age, 36 years; 51% with bites on upper extremities) and 82% of rattlesnake bite patients (median age, 42.5 years; 76% on upper extremities). All patients except one were treated at a healthcare facility with > 80% arriving within 6 hours following the bite. Over 60% of patients received crotaline Fab antivenom; no patients received the older Antivenin Crotalidae Polyvalent. Severity of the envenomation for copperheads and rattlesnakes was classified as dry (7.74%, 13.16%), mild (68.39%, 73.68%), moderate (22.58%, 10.53%), and severe (1.39%, 2.63%), respectively. Seventeen of 156 patients (10.89%) developed abnormal hematologic laboratory results following copperhead bites and two of 38 (5.26%) patients developed abnormal hematologic laboratory parameters with rattlesnake bites. Of these, the most common abnormality was coagulopathy (16/17 = 94.11%; 2/2 = 100%), followed by hypofibrinogenemia (5/17 = 29.41%; 0/0 = 0.00%) and thrombocytopenia (2/17 = 11.76%; 0/0 = 0.00%) for copperheads and rattlesnakes respectively. Recurrence phenomena was observed in 4 patients with copperhead bites and 2 patients with rattlesnake bites, while delayed onset of symptoms were seen in 12 patients and 5 patients, respectively. Among those experiencing recurrence, 75% of patients bitten by copperheads experienced local effects including pain and swelling and 25% experienced coagulopathy, while a 100% of the patients bitten by rattlesnakes experienced recurrent local effects. Among those experiencing a delayed onset of symptoms, 90% of the patients with copperhead bites experienced coagulopathy while 10% had local effects and 100% of the patients bitten by rattlesnakes experienced coagulopathy. Reaction to the antivenom developed in three patients. Three patients underwent a fasciotomy.

Antivenom therapy is typically administered to halt the progression of local envenomation effects and improve abnormal hematologic parameters towards normal. In South Carolina, the primary indication for antivenom treatment is most commonly to treat local clinical findings. Our poison center experience suggests coagulopathy is the most common hematologic laboratory abnormality following crotaline envenomation in addition to a low rate of thrombocytopenia in our geographic location. Other geographic areas of the United States are recognized to have more frequent and severe hematologic complications following crotaline bites.

Bennett:Pfizer: Consultancy.