Lipid emulsion therapy during management of the critically-ill poisoned patient: a prospective cohort study.

BACKGROUND: Despite conflicting data, intravenous lipid emulsion has emerged as a potential antidote. The "lipid sink" theory suggests that following intravenous administration of lipid, lipophilic drugs are sequestered in the vascular compartment, thereby reducing their tissue concentrations. This study sought to determine if survival is associated with the intoxicant's degree of lipophilicity. METHODS: We reviewed all cases in the Toxicology Investigators Consortium's lipid sub-registry between May 2012 through December 2018. Information collected included demographics, exposure circumstances, clinical course, management, disposition, and outcome. The primary outcome was survival after lipid emulsion therapy. Survival was stratified by the log of the intoxicant's octanol-water partition coefficient. We also assessed the association between intoxicant lipophilicity and an increase in systolic blood pressure after lipid emulsion administration. RESULTS: We identified 134 patients, including 81 (60.4%) females. The median age was 40 years (interquartile range 21-75). One hundred and eight (80.6%) patients survived, including 45 (33.6%) with cardiac arrest during their intoxication. Eighty-two (61.2%) were hypotensive, and 98 (73.1%) received mechanical ventilation. There was no relationship between survival and the log of the partition coefficient of the intoxicant on linear analysis (P = 0.89) or polynomial model (P = 0.10). Systolic blood pressure increased in both groups. The median (interquartile range) systolic blood pressure before lipid administration was 68 (60-78) mmHg for those intoxicants with a log partition coefficient < 3.6 compared with 89 (76-104) mmHg after lipid administration. Among those drugs with a log partition coefficient > 3.6, the median (interquartile range) was 69 (60-84) mmHg before lipid and 89 (80-96) mmHg after lipid administration. CONCLUSION: Most patients in this cohort survived. Lipophilicity was not correlated with survival or the observed changes in blood pressure. The study did not address the efficacy of lipid emulsion.

Management of Acetaminophen Poisoning in the US and Canada: A Consensus Statement.

Importance: The US and Canada currently have no formal published nationwide guidelines for specialists in poison information or emergency departments for the management of acetaminophen poisoning, resulting in significant variability in management. Objective: To develop consensus guidelines for the management of acetaminophen poisoning in the US and Canada. Evidence Review: Four clinical toxicology societies (America's Poison Centers, American Academy of Clinical Toxicology, American College of Medical Toxicology, and Canadian Association of Poison Control Centers) selected participants (n = 21). Led by a nonvoting chairperson using a modified Delphi method, the panel created a decision framework and determined the appropriate clinical management of a patient with acetaminophen poisoning. Unique to this effort was the collection of guidelines from most poison centers in addition to systematic collection and review of the medical literature. Comments from review by external organizations were incorporated before the guideline was finalized. The project began in March 2021 and ended in March 2023. Findings: The search retrieved 84 guidelines and 278 publications. The panel developed guidelines for emergency department management of single or repeated ingestion of acetaminophen. In addition, the panel addressed extended-release formulation, high-risk ingestion, coingestion of anticholinergics or opioids, age younger than 6 years, pregnancy, weight greater than 100 kg, and intravenous acetaminophen use. Differences from current US practice include defining acute ingestion as an ingestion presentation from 4 to 24 hours after overdose was initiated. A revised form of the Rumack-Matthew nomogram was developed. The term massive ingestion was replaced with the term high-risk ingestion and denoted by a specific nomogram line. Other recommendations include specific criteria for emergency department triage, laboratory evaluation and monitoring parameters, defining the role of gastrointestinal decontamination, detailed management of acetylcysteine treatment, associated adverse effects, and stopping criteria for acetylcysteine treatment, as well as criteria for consultation with a clinical toxicologist. Finally, specific treatment considerations, including acetylcysteine dosing, fomepizole administration, and considerations for extracorporeal elimination and transplant evaluation, were addressed. Conclusions and Relevance: This qualitative study provides a consensus statement on consistent evidence-based recommendations for medical, pharmacy, and nursing education and practice to optimize care of patients with acetaminophen poisoning.

Compartment Syndrome after Crotalid Envenomation in the United States: A Review of the North American Snakebite Registry from 2013 to 2021 on Behalf of the ToxIC Snakebite Study Group.

INTRODUCTION: Compartment syndrome (CS) is a rare but serious complication after crotalid envenomation in the United States. Few data are available regarding the epidemiology and management of these cases. Significant controversy and misunderstanding over best practices, including measurement of compartment pressures and use of fasciotomy, exist for this syndrome. This study aims to describe presentation and management of suspected CS cases after native snakebite reported to the North American Snakebite Registry (NASBR). METHODS: This is an analysis of snakebite cases reported to the Toxicology Investigators Consortium NASBR between January 1, 2013 and December 31, 2021. Cases of native snakebite with documented concern for CS were included. RESULTS: Over an 8-y period, 22 cases of suspected CS were identified, representing 1% of all cases reported to the NASBR. Fasciotomies were performed in 41% (n=9) of these cases, most commonly to the upper extremity (67%, n=6). In cases of suspected CS, intracompartmental pressures (ICPs) were rarely measured (23%, n=5) and fasciotomies were performed without measurement of ICPs frequently (56%, n=5). In 1 case, ICPs were measured and found to be low (8 mm Hg) and fasciotomy was avoided. CONCLUSIONS: Measurement of compartment pressures in cases of suspected CS was uncommon in cases reported to the NASBR. Fasciotomy was commonly performed without measurement of compartment pressures.

Clinical Presentations, Treatments, and Outcomes of Non-native Snake Envenomations in the United States Reported in the North American Snakebite Registry.

BACKGROUND: Non-native snake envenomations in the United States are uncommon with much unknown about a patient's presenting signs and symptoms. Antivenoms for non-native snake envenomations are not typically available in hospital pharmacies which may limit their administration. What are the clinical presentations, treatments, and outcomes of non-native snake envenomation cases reported to the North American Snakebite Registry (NASBR) of the Toxicology Investigators Consortium (ToxIC)? METHODS: This is a descriptive review of all non-native envenomations reported to the NASBR from 2013 to March 2022. Data abstracted included snake species, patient history, clinical signs, diagnostics, treatment (including antivenom usage), follow-up, and final outcome. RESULTS: We identified 19 non-native snake envenomations resulting from encounters with eleven different species, eight of which belonged to the Viperidae family. The most common presenting symptoms were edema (18 patients), ecchymosis (seven patients), and necrosis (six patients). Systemic effects and hematologic abnormalities were less common. The most common treatments were extremity elevation and analgesia, with two patients receiving mechanical ventilation. Ten patients received antivenom. No patients died. Three patients had loss of mobility in a digit at the last follow-up visit. One patient had permanent tissue loss of a small area on a finger. CONCLUSIONS: The results of this study suggest that non-native snake envenomations in the United States frequently cause local soft tissue effects and less frequently cause systemic or hematologic effects. Most patients received antivenom, although several patients envenomated by snakes for which a specific antivenom exists did not receive any. Sequelae at the last follow-up of such encounters consisted of local mobility deficits.

North American Envenomation Syndromes.

This review discusses the distinct envenomation syndromes produced by North American species of snakes and arthropods, specifically the Crotalinae subfamily of snakes, which includes cottonmouths, copperheads, and rattlesnakes; coral snakes; Latrodectus and Loxosceles species of arachnid; and Centruroides sculpturatus, the only species of North American scorpion capable of producing an envenomation syndrome. The authors discuss the epidemiology, pathophysiology, and presentation of these syndromes and emphasize the varying degrees to which these syndromes can manifest clinically. Finally, the management of each envenomation syndrome is addressed. Special attention is paid to available antivenoms, their indications for use, and their side effects.

Late hemotoxicity following North American rattlesnake envenomation treated with crotalidae immune F(ab')2 (equine) antivenom and crotalidae immune polyvalent Fab (ovine) antivenom reported to the North American Snakebite Sub-registry.

INTRODUCTION: Late hemotoxicity is common following rattlesnake envenomation treated with crotalidae immune polyvalent Fab (ovine) (FabAV). Initial clinical trials showed crotalidae immune F(ab')2 (equine) (Fab2AV) to be superior to FabAV in preventing late hemotoxicity, but this effect has not been demonstrated in broader populations. This study investigated late hemotoxicity in patients receiving Fab2AV or FabAV after rattlesnake envenomation. METHODS: This is a retrospective analysis of prospectively collected data from patients with snakebite reported to the ToxIC North American Snakebite Registry (NASBR) between January 1, 2019, and December 31, 2020. Inclusion criteria were rattlesnake envenomation and administration of antivenom. Patients were excluded if they received more than one type of antivenom. The primary outcome was occurrence of late hemotoxicity (platelets ≤120 k/mm3 or fibrinogen ≤170 mg/dL) in patients receiving Fab2AV and FabAV. Data collected included demographics, envenomation characteristics, laboratory values, and treatment administered. Statistics including t-test and Fisher's exact test were used. RESULTS: A total of 201 rattlesnake envenomated patients receiving antivenom were reported to the NASBR in the study period; 144 were included. 49 received Fab2AV alone, 45 received FabAV alone and 50 received both antivenoms. Baseline patient and envenomation characteristics were similar between the groups. Late hemotoxicity occurred in 2/49 patients in the Fab2AV group (4% (95% CI 0.7-12.6)) and in 19/45 patients in the FabAV group (42% (95% CI 28.4-59.0); absolute risk reduction 39.1% (95% CI 21.2-46.2) (p = 0.001). On follow up, 0 patients (0%) receiving Fab2AV were retreated with antivenom; 4 patients (9%) receiving FabAV were retreated (p = 0.049). CONCLUSIONS: In the North American Snakebite Registry, late hemotoxicity was less common in rattlesnake envenomated patients treated with Fab2AV compared to FabAV.

Early Experience with Crotalidae Immune F(ab')2 Antivenom to Treat Arizona Rattlesnake Envenomations.

INTRODUCTION: Crotalidae immune F(ab')2 (Fab2AV) became available in the USA in 2019 for treatment of rattlesnake envenomation. In the clinical trial comparing Fab2AV to crotalidae immune polyvalent fab (FabAV), Fab2AV was associated with less late hemotoxicity. The purpose of this study was to describe outcomes following use of Fab2AV in patients with rattlesnake envenomation in Arizona. METHODS: This is an observational study of patients admitted to a medical toxicology service at two hospitals in Arizona between January 1, 2019 and December 31, 2020. Patients with rattlesnake envenomation who received Fab2AV were included. Patients who received FabAV, alone or in combination with Fab2AV, were excluded. The main outcomes of interest were antivenom dose, adverse reactions, late hemotoxicity, and hospital readmission or retreatment. RESULTS: Forty-six patients were included. The mean age was 40 years, with 15% under 12 years of age. All exhibited swelling, 20% thrombocytopenia, and 35% coagulopathy. Median time to treatment was 3 h and median total Fab2AV dose was 20 vials. Three patients had an acute reaction to Fab2AV which was non-life-threatening and resolved with antihistamines and/or steroids. In the follow-up period, one case of delayed thrombocytopenia (platelets = 108 K/mm3) and one case of recurrent thrombocytopenia (platelets = 111 K/mm3) were identified. There was no late coagulopathy. Five patients reported symptoms consistent with mild serum sickness. CONCLUSIONS: In this series of patients with rattlesnake envenomation in Arizona who were treated with Fab2AV, there were no cases of clinically significant late hemotoxicity, and no patients required late retreatment with antivenom. Acute and delayed reactions did occur in some patients but were mild and easily treated.

Chloroquine Ingestion to Prevent SARS-CoV-2 Infection: A Report of Two Cases.

INTRODUCTION: Amid the global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), chloroquine and hydroxychloroquine were being studied as agents to prevent and treat coronavirus disease 2019. Information about these agents and their effects circulated throughout the general public media, raising the concern for self-directed consumption of both pharmaceutical and non-pharmaceutical products. CASE REPORT: We present two cases of chloroquine toxicity that occurred after ingestion of an aquarium disinfectant that contained chloroquine phosphate in a misguided attempt to prevent infection by SARS-CoV-2. One patient had repeated emesis and survived, while the other was unable to vomit, despite attempts, and suffered fatal cardiac dysrhythmias. CONCLUSION: These cases illustrate the spectrum of toxicity, varied presentations, and importance of early recognition and management of chloroquine poisoning. In addition, we can see the importance of sound medical guidance in an era of social confusion compounded by the extremes of public and social media.

Epidemiology, Clinical Features, and Management of Texas Coral Snake (Micrurus tener) Envenomations Reported to the North American Snakebite Registry.

INTRODUCTION: Few of the 5000-8000 snakebites reported to poison control centers annually in the USA are attributed to coral snakes. This study describes Texas coral snake envenomations reported to the North American Snakebite Registry. METHODS: All Texas coral snake envenomation cases reported to the registry were identified for the period from January 1, 2015, through December 31, 2019. Data reviewed for this study included details regarding the snake encounter, patient demographics, signs and symptoms, treatment, and outcomes. Descriptive statistics were used to report results. RESULTS: Ten men and four nonpregnant women reported coral snake bites. The median patient age was 15.5 (range 5-72 years). There were 12 upper extremity bites and two bites to the lower extremity. The most common symptoms reported were paresthesias and pain. All subjects had paresthesias, often described as an "electric" sensation. Seven patients described them as painful. The most common clinical findings were erythema and swelling. No patient developed tissue damage, hematotoxicity, rhabdomyolysis, hypotension, weakness, or respiratory symptoms. Thirteen subjects were treated with opioids. Six patients were treated with antiemetics: three prophylactically and two for opioid-induced nausea. One patient developed nausea and non-bloody, nonbilious emesis within 1 hour of the bite, prior to receiving opioids. No patients were treated with antivenom. Antibiotics were not administered to any patient, and no infections were reported. CONCLUSIONS: Envenomations from M. tener in Southeast Texas are characterized by painful paresthesias. Mild swelling and erythema are common. Neurotoxicity necessitating antivenom or mechanical ventilation did not occur.

One Bite, Two Patients: Disparate Clinical Courses Following Simultaneous Crotalus oreganus abyssus Envenomation.

A number of crotaline species have been associated with neurotoxic envenomation in North America. One clinical sign that can occur is myokymia: fine, involuntary, wave-like muscle movements occurring at regular intervals. We report an unusual scenario in which a single snakebite resulted in simultaneous envenomation of 2 patients. Both developed myokymia, with 1 having respiratory compromise. One patient also developed a hypersensitivity reaction to antivenom. Envenomation by the Grand Canyon rattlesnake, Crotalus oreganus abyssus, can produce significant neurotoxicity and resultant respiratory compromise. Antivenom may be helpful but can produce hypersensitivity reactions.

When It Comes to Snakebites, Kids Are Little Adults: a Comparison of Adults and Children with Rattlesnake Bites.

BACKGROUND: Rattlesnake envenomations are a significant cause of morbidity in the USA. While pediatric rattlesnake envenomations are relatively common, data comparing adult and pediatric patients with rattlesnake envenomations remain limited. METHODS: This multi-center retrospective study used the North American Snakebite Registry (NASBR), a sub-registry of the Toxicology Investigator's Consortium (ToxIC). All cases of rattlesnake envenomations between January 1, 2013, and December 31, 2017, which were entered into the NASBR, were reviewed. Clinical and laboratory parameters, as well as treatment and outcome measurements, were compared between adult and pediatric patients. RESULTS: A total of 420 unique cases were identified, including 94 pediatric patients. Adult patients were more likely to be male (76% vs. 62%; OR 1.98) and sustain upper extremity envenomations (57% vs. 25%; OR 4.4). After adjusting for bite location, adults were more likely to exhibit edema compared with pediatric patients. After controlling for envenomation location, there was no difference in rates of necrosis between adult and pediatric patients. Adults exhibited early hematologic toxicity less frequently than pediatric patients, but there was no difference in the rates of late hematologic toxicity. There were no differences in the rates of hypotension or intubation. CONCLUSION: While adult and pediatric patients have some differences in envenomation characteristics and laboratory parameters, adults and pediatric patients had similar rates of systemic toxicity, severity, length of stay, and late hematologic toxicity.

Bupropion associated seizures following acute overdose: who develops late seizures.

Objectives: Bupropion is an antidepressant that is commonly known to cause seizures in overdose. Because of concern for delayed onset of seizures, patients are frequently observed for prolonged periods after overdose. The primary objective is to evaluate the incidence and clinical parameters associated with late seizures following bupropion overdose.Methods: This retrospective study of acute bupropion overdose who presented to 26 different hospitals in California and Arizona during an 8 year time period.Results: 437 patients were identified. Tachycardia and altered mental status were common. A total of 122 (27.9%) patients had seizures following their overdose. Only eight patients (1.8%) had a seizure more than 8 h after hospital arrival. None of these patients were asymptomatic on arrival. Among patients with tachycardia on arrival, the odds of having a seizure was 6.7 (95% CI 3.7-10.9); the odds of a seizure more than 8 h after arrival was 5.24 (95% CI 1.2-23.5). Similarly, altered mental status on arrival was significantly associated with the risk of a seizure; OR 3.93 (95% CI 2.21-7.0).Conclusion: Seizures are relatively common, and are associated with antecedent tachycardia or altered mental status.

The Relationship Between Circulating Acetaminophen-Protein Adduct Concentrations and Alanine Aminotransferase Activities in Patients With and Without Acetaminophen Overdose and Toxicity.

INTRODUCTION: Measurement of serum acetaminophen-protein adducts (APAP-CYS) has been suggested to support or refute a diagnosis of acetaminophen (APAP)-induced hepatotoxicity when ingestion histories are unreliable or unavailable and when circulating APAP concentrations are low or undetectable. Non-APAP overdose patients commonly have used APAP products in non-toxic quantities and, thus, will have measurable APAP-CYS concentrations, even when hepatic injury results from other causes, such as ischemic hepatitis. The relationship between alanine aminotransferase (ALT) activity and APAP-CYS concentration might assist in distinguishing between toxic and non-toxic APAP doses in patients suspected of drug overdose. METHODS: We measured serial levels of serum APAP-CYS and ALT activities in 500 overdose patients in whom APAP toxicity was suspected on inpatient admission, but who were then classified at time of discharge and before results of APAP-CYS concentrations were available into three groups: 1) definite APAP group; 2) definitely not APAP group; and 3) indeterminate group. Subjects in the definite and definitely not APAP groups were selected in whom a plasma ALT activity was measured within ± 4 h of a serum APAP-CYS concentration. Regressions with correlation coefficients between APAP-CYS and ALT were calculated for repeat measures in the 335 subjects (908 blood samples) in the definite APAP group and 79 subjects (231 samples) in the definitely not APAP group, with an emphasis on APAP-CYS concentrations and calculation of 95% prediction intervals when ALT was ≥ 1000 IU/L. RESULTS: A strong correlation was found between APAP-CYS and ALT in the definite APAP group over all ALT activities (r = 0.93, p < 0.001; N = 335), and when ALT was > 1000 IU/L (r = 0.82, p < 0.001, N = 144). In the 79 definitely not APAP subjects, no significant correlation was found when ALT exceeded 1000 IU/L (r = 0.04; p = 0.84, N = 32). All subjects in the definitely not APAP group displayed APAP-CYS concentrations < 3 µM. In definitely not APAP subjects, the great majority of APAP-CYS levels were below the 95% prediction interval for APAP-CYS concentrations in definite APAP group subjects when ALT was ≥ 1000 IU/L. However, some definitely not APAP group subjects who had ingested non-toxic doses of APAP displayed APAP-CYS concentrations as high as 2.8 µM in the face of ALT elevation from ischemic hepatitis. CONCLUSION: The interpretation of serum APAP-CYS concentrations must always be made in light of detailed clinical information and the population being tested, especially because of some overlap in APAP-CYS levels in subjects with and without APAP toxicity.

Rattlesnake venom-induced recurrent coagulopathy in first trimester pregnant women - Two Cases.

Delayed or recurrent coagulopathy can occur up to 14 days after North American rattlesnake envenomation in patients that have been treated with Crotalidae Polyvalent Immune Fab (CroFab). There is little data in the literature characterizing the sequelae of North American rattlesnake envenomation in pregnancy and no previously published reports of recurrent coagulopathy in pregnancy. CASE REPORT: We present 2 cases of first trimester pregnant women requiring readmission and retreatment with Crotalidae Polyvalent Immune Fab (CroFab) after developing recurrent/late coagulopathy following North American Rattlesnake Envenomation. Both patients were initially admitted and treated with CroFab following snakebite and discharged home without coagulopathy. One patient developed significant hypofibrinogenemia and subsequent hemorrhage after spontaneous abortion secondary to recurrent venom induced hypofibrinogenemia. DISCUSSION: Pregnant women with recurrent or late coagulopathy may be at higher risk for hemorrhage and spontaneous abortion and require more frequent laboratory monitoring after initial hospitalization and treatment with antivenom. A lower threshold for re-treatment with CroFab may be warranted in patients with fibrinogen less than 100mg/dL even in the setting of a normal platelet count.

The Virtual Toxicology Journal Club: the Dissemination and Discussion of Noteworthy Manuscripts Using Twitter.

BACKGROUND: Twitter-based chat groups (tweetchats) structured as virtual journal clubs have been demonstrated to provide value to learners. In order to promote topics in medical toxicology, we developed the #firesidetox tweetchat as a virtual journal club to discuss and disseminate topics in medical toxicology. METHODS: A group of medical toxicologists from the American College of Medical Toxicology (ACMT) Public Affairs Committee and editorial board of the Journal of Medical Toxicology (JMT) developed a quarterly one hour tweetchat featuring JMT manuscripts. We gathered basic twittergraphics and used a healthcare hashtag aggregator to measure the number of impressions, participants, and tweets per tweetchat session. A qualitative analysis of important themes from #firesidetox was also completed. RESULTS: During five tweetchats over 12 months, we attracted a mean of 23 participants generating a mean of 150 tweets per #firesidetox tweetchat. Tweets generated a mean of 329,200 impressions (unique user views): these impressions grew by 300% from the first through fifth #firesidetox. The majority of participants self-identified as medical toxicologists or physician learners. Although most were from the USA, participants also came from Australia, Poland, and Qatar. Most tweets centered on medical education and 7.9% tweets were learner-driven or questions asking for a medical toxicologist expert opinion. CONCLUSION: The #firesidetox attracted a diverse group of toxicologists, learners, and members of the public in a virtual journal club setting. The increasing number of impressions, participants, and tweets during #firesidetox demonstrates the tweetchat model to discuss pertinent toxicology topics is feasible and well received among its participants.

Acute adverse events associated with the administration of Crotalidae polyvalent immune Fab antivenom within the North American Snakebite Registry.

Background: Crotalidae Polyvalent Immune Fab (Fab Antivenom) is the primary Viperid antivenom used in the United States since 2000. Adverse event data associated with its use are limited. The purpose of this study is to describe the prevalence of acute adverse events associated with the use of Fab antivenom. Methods: The American College of Medical Toxicology's Toxicology Investigators Consortium maintains a prospective case registry of poisoned and envenomated patients managed by medical toxicologists at the bedside. This registry includes the North American Snakebite sub-registry. We performed a review of 438 cases entered into the Snakebite sub-registry. Results: A total of 373 (85.2%) received at least one vial of Fab Antivenom. Forty percent were children. Adverse events occurred in 10 patients (2.7%) of whom six were adults. Rash was the most common adverse event. More severe adverse events (hypotension, bronchospasm, and/or angioedema) occurred in four (1.1%) patients. Prophylaxis was administered prior to Fab antivenom in 4.0%. Eight patients received various treatments for their adverse events. Neither the initial number of Fab antivenom vials, atopic history, nor prior envenomation correlated with the prevalence of adverse events. Discussion: This prevalence of adverse events was lower than in previous studies and in a meta-analysis of 11 studies. The types of adverse events and treatments used are consistent with those in previous reports. There were no prior reports of prophylaxis use with which to compare. Conclusion: The prevalence of Fab antivenom adverse events in the North American Snakebite Registry was 2.7%.

Comparison of Antivenom Dosing Strategies for Rattlesnake Envenomation.

OBJECTIVES: This study compares maintenance with clinical- and laboratory-triggered (as-needed [PRN]) antivenom dosing strategies with regard to patient-centered outcomes after rattlesnake envenomation. DESIGN: This is a retrospective cohort study of adult rattlesnake envenomations treated at a regional toxicology center. Data on demographics, envenomation details, antivenom administration, length of stay, and laboratory and clinical outcomes were compared between the PRN and maintenance groups. Primary outcomes were hospital length of stay and total antivenom used, with a hypothesis of no difference between the two dosing strategies. SETTING: A single regional toxicology center PATIENTS:: Three-hundred ten adult patients envenomated by rattlesnakes between 2007 and 2014 were included. Patients were excluded if no antivenom was administered or for receiving an antivenom other than Crofab (BTG International, West Conshohocken, PA). INTERVENTIONS: This is a retrospective study of rattlesnake envenomations treated with and without maintenance antivenom dosing. MAIN RESULTS: One-hundred forty-eight in the maintenance group and 162 in the PRN group were included. There was no difference in demographics or baseline envenomation severity or hemotoxicity (32.7% vs 40.5%; respectively; p = 0.158) between the two groups. Comparing the PRN with the maintenance group, less antivenom was used (8 [interquartile range, 6-12] vs 16 [interquartile range, 12-18] vials, respectively; p < 0.001), and hospital length of stay was shorter (27 hr [interquartile range, 20-44 hr] vs 34 hr [interquartile range, 24-43 hr], respectively; p = 0.014). There were no differences in follow-up outcomes of readmission, retreatment, or bleeding and surgical complications. CONCLUSIONS: Hospital length of stay was shorter, and less antivenom was used in patients receiving a PRN antivenom dosing strategy after rattlesnake envenomation.