Initial postmarketing experience with Crotalidae polyvalent immune Fab for treatment of rattlesnake envenomation

Study objective: We describe our postmarketing experience with patients receiving Crotalidae polyvalent immune Fab (CroFab; FabAV) antivenom for treatment of rattlesnake envenomation. Methods: The charts of 28 patients admitted between March 1 and September 9, 2001, with rattlesnake envenomation and treated with FabAV were reviewed for demographic information, time until antivenom treatment, laboratory findings, evidence of hypersensitivity reaction, length of hospital stay, and readmission to the hospital. Results: All patients had swelling, 20 patients had elevated prothrombin times (>14 seconds), 12 patients had low fibrinogen levels (<170 mg/dL), and 6 patients had thrombocytopenia (platelet count <120, 000/mm³) on presentation. The total dose of FabAV ranged from 10 to 47 vials per patient. Hypofibrinogenemia was resistant to FabAV in some patients. On follow-up, recurrence of coagulopathy was detected in 3 patients, and recurrence of thrombocytopenia was detected in 1 patient. Two patients demonstrated delayed-onset severe thrombocytopenia. Recurrence or delayed-onset toxicity might have been underestimated because of incomplete follow-up in some patients. No acute hypersensitivity reactions occurred. Two patients reported mild symptoms of possible serum sickness on follow-up. Conclusion: FabAV effectively controlled the effects of envenomation; however, initial control of coagulopathy was difficult to achieve in some cases, and recurrence or delayed-onset hematotoxicity was common. When initially managing hematotoxicity, a trend toward normalization of laboratory values might be a more reasonable end point for FabAV treatment than attainment of normal reference values in nonbleeding patients.