Rattlesnake venom-induced thrombocytopenia response to antivenin (Crotalidae) polyvalent: A case series

Objective: To test the hypothesis that rattlesnake venom-induced thrombocyt openia would improve following Antivenin (Crotalidae) Polyvalent administra tion, and that the degree of platelet increase would correlate with the dos age of antivenom. Methods: The authors conducted a retrospective review of all patients admitted for rattlesnake envenomation at two southern Californ ia hospitals between 1980 and 1998. Patients were included if platelet coun t was less than 150 x 10(9)/L following a rattlesnake bite. Patients were e xcluded if they received platelet transfusion. The relationship between Ant ivenin (Crotalidae) Polyvalent administration and venom-induced thrombocyto penia was evaluated by linear regression and paired t-test. Results: The au thors identified 103 cases of rattlesnake envenomation. Seventeen cases met inclusion criteria for thrombocytopenia. Two patients were excluded becaus e they received platelet transfusions. One additional patient was excluded from paired t-test only because no antivenom was given. Thrombocytopenia us ually improved between presentation and discharge (mean difference, 44 x 10 (9)/L), although complete resolution was often not achieved. A statisticall y significant partial improvement in platelet counts immediately after anti venom administration was observed in a subset of patients with severe throm bocytopenia (platelet count <100 x 10(9)/L) (mean difference, 64 x 10(9)/L) . Using regression analysis, the authors did not detect a linear relationsh ip between the amount of Antivenin (Crotalidae) Polyvalent administered and the degree of improvement. Conclusions: Although rattlesnake venom-induced thrombocytopenia usually improves immediately after Antivenin (Crotalidae) Polyvalent administration and by the time of discharge, the degree of impr ovement is frequently incomplete and of uncertain clinical significance in the absence of life-threatening bleeding. The authors found no correlation between the degree of improvement and the dosage of Antivenin (Crotalidae) Polyvalent.