Comparison of F(ab')2 and Fab antivenoms in rattlesnake envenomation: First year's post-marketing experience with F(ab')2 in New Mexico.

Two antivenoms are available for rattlesnake envenomations in the U.S., Fab (CroFab®, BTG, UK), and F(ab')2 (Anavip®, Bioclon, Mexico) antivenom (AV) with F(ab')2AV released in October 2018. The F(ab')2AV Phase 3 comparative clinical trial demonstrated similar efficacy in treating venom-caused hematologic toxicity, similar rates of Types I and III hypersensitivity reactions, and a lower rate of recurrent hematological effects than FabAV. We hypothesized that a post-marketing, comparative study of effectiveness and rates of hypersensitivity reactions in treating rattlesnake envenomations in New Mexico would demonstrate similar outcomes. Patients eligible for the study presented to a New Mexico healthcare facility between May and October 2019 and were known/suspected to have a rattlesnake bite. Exclusion criteria for antivenom comparison were those with a dry bite, lost to follow-up, or late presentation. All cases were included for patient/bite demographics, initial local control, hematological control, number of maintenance/control doses, development of persistent, recurrent or late-, new-onset hematologic effects, and hypersensitivity reactions. We used Fisher's exact tests for analysis and 0.05 cutoff to determine significance. There were 54 rattlesnake-bitten patients in New Mexico with 17 excluded for comparison of antivenom because of dry bites, loss to follow-up, and one case of late presentation. Thirty-seven patients remained for comparative analysis between F(ab')2AV (n = 11) and FabAV (n = 26). There were no significant demographic differences between F(ab')2 and Fab-treated patients. No patient had a Type I hypersensitivity reaction. No rescue doses were given. The rate of recurrent, persistent or late-, new-onset of hematologic effects was 0% with F(ab')2AV and 29% with FabAV. No patient was readmitted. No patient had bleeding complications. Type III hypersensitivity reactions were similar between F(ab')2AV (36%) and FabAV (25%). The results of our study are consistent with the Phase 3 clinical comparative trial and indicate no significant differences in safety or effectiveness between FabAV and F(ab')2AV. F(ab')2AV offers the advantages of not requiring maintenance doses and may have a lower rate of late hematologic effects in treating rattlesnake envenomations.

Unpredicted late-, new-onset thrombocytopenia and hypofibrinogenemia in Fab antivenom-treated rattlesnake envenomation.

The use of Fab antivenom (Crotalidae Polyvalent Immune Fab (Ovine) (CroFab); Boston Scientific) against North American Crotalidae envenomation is associated with the development of late- (≥4 days post-envenomation), new-onset of hematological abnormalities. Although attempts have been made to identify predictive indicators during the acute phase of an envenomation, of patients who are not at-risk of late-, new-onset of hematological abnormalities, there has been at least one prior report of a patient who developed thrombocytopenia that was unpredicted by current indicators. We add three cases of unpredicted, late-, new-onset of hematological abnormalities in patients with Fab-treated rattlesnake bite.

Envenomations during pregnancy reported to the national poison data system, 2009-2018.

Envenomations during pregnancy have consequences affecting both maternal and fetal outcomes. U.S. poison center data on envenomations offers a comparative view of envenomations in pregnant and non-pregnant women. The National Poison Data System of the American Association of Poison Control Centers was searched for cases of envenomation during pregnancy between January 1, 2009 and December 31, 2018 and compared with exposures to non-pregnant females of childbearing age. Odds ratios and descriptive statistics were used where appropriate. There were a total of 3,555 venomous animal exposures in pregnant women during this 10-year period, most commonly with scorpion stings. These were compared with 87,553 envenomations in non-pregnant women of childbearing age during that time period. Overall, drug treatment was administered in 350 (9.9%) cases of envenomation in pregnant women compared with 21,381 (24.4%) of non-pregnant patients. Antihistamines were less likely to be used in pregnant patients with scorpion (1.8% v. 9.2%), hymenoptera (bee, wasp, or hornet) (12.4% v. 37.1%), black widow spider (2.8% v. 8.1%), and caterpillar (10.4% v. 37.7%) exposures. There was an increased likelihood of antivenom use during pregnancy with rattlesnake envenomations (85.0% v. 58.9%) and black widow spider bites (4.8% v. 2.2%). There were no maternal deaths, and most maternal outcomes were coded as having no (1.0%) or minor (87.6%) effects. Three fetal deaths occurred, all following snakebites and all before 20 weeks gestation. Two were attributed as related, and one as of uncertain relationship to the exposure, by the managing poison centers. Most envenomations caused no or minor effects to pregnant women.