Thrombocytopenia following timber rattlesnake envenomation

Study objective: To better characterize timber rattlesnake venom-induced thrombocytopenia and coagulopathy and the response to therapy with Antivenin (Crotalidae) Polyvalent. Methods: We conducted a retrospective multicenter review of timber rattlesnake envenomation. Results: We reviewed 18 cases at two institutions. Restoration of normal prothrombin time and partial thromboplastin time was achieved in all cases with antivenom therapy. In contrast, complete reversal of thrombocytopenia was not achieved, despite antivenom therapy. Conclusion: Antivenin (Crotalidae) Polyvalent was less effective in reversing thrombocytopenia than coagulopathy after timber rattlesnake envenomation, suggesting that a component of timber rattlesnake venom persists in the blood despite antivenom therapy. Persistent thrombocytopenia may be due to a venom factor that the antivenom does not neutralize or to inadequate dosing of antivenom. Prompt reversal of thrombocytopenia following treatment of timber rattlesnake envenomation with this antivenom appears unlikely.