Recurrent and persistent coagulopathy following pit viper envenomation

North American poisonous bites and stings

Critters and creatures can strike fear into anyone who thinks about dangerous animals. This article focuses on the management of the most common North American scorpion, arachnid, hymenoptera, and snake envenomations that cause clinically significant problems. Water creatures and less common animal envenomations are not covered in this article. Critical care management of envenomed patients can be challenging for unfamiliar clinicians. Although the animals are located in specific geographic areas, patients envenomed on passenger airliners and those who travel to endemic areas may present to health care facilities distant from the exposure.

Continuous IV Crotalidae Polyvalent Immune Fab (Ovine) (FabAV) for selected North American rattlesnake bite patients

BACKGROUND

In patients bitten by North American rattlesnakes and treated with Crotalidae Polyvalent Immune Fab (Ovine) (FabAV), late hematologic abnormalities-persistent, recurrent, or late, new onset of hypofibrinogenemia, prolonged PT/INR, prolonged PTT, and/or thrombocytopenia beyond 48 h post-envenomation-are common, difficult to manage, and may result in morbidity and mortality are common, difficult to manage, and may result in morbidity and mortality. The optimal management of late hematologic abnormalities, particularly the use of further treatment with antivenom, has not been well defined. The current FabAV treatment regimen is to give antivenom as a bolus dose over a one-hour period. We describe our experience using a continuous intravenous infusion of FabAV for late hematologic effects and/or associated bleeding complications in rattlesnake envenomation.

METHODS

This is a retrospective, observational case series of patients envenomated by North American rattlesnakes at three medical centers managed with a continuous intravenous infusion of FabAV for late hematologic abnormalities and/or associated bleeding complications. Indications, dilution and infusion protocols, and duration of therapy were individualized.

RESULTS

Five cases were identified between July 2010 and September 2011. All patients had profound late hematologic abnormalities and/or were associated with bleeding complications. Several patients had received repeat bolus infusions of FabAV, with or without human blood products, with either inadequate or only transient beneficial response. All patients were then managed with a continuous intravenous infusion of FabAV and all appeared to respond to the continuous intravenous infusion of FabAV, titrated to effect, with cessation of progression and, in most cases, improvement in hematologic abnormalities. Rates of infusion varied from 2 to 4 vials per 24 h (mean = 3.1 ± 0.4 vials/day). The termination of FabAV infusion was between day 6 and day 14 from the time of envenomation (mean = 10 ± 3 days), after which hematologic values were normalized or were normalizing in all patients and continued to do so.

DISCUSSION

The use of FabAV as a continuous intravenous infusion, particularly after the acute phase of envenomation has passed, provides a continuous source of circulating antibodies to neutralize venom components reaching circulation from tissue stores and allows natural replenishment of hematologic factors such as platelets and/or fibrinogen. This method is an efficient use of FabAV, avoiding the wasteful excess of a bolus dose, may be more effective, eliminating the potential for destruction of hematologic factors when protective antivenom levels are lost between bolus FabAV doses, and appears to be safe. Further assessments of the stability and sterility of the product during infusion are needed. The need to continue hospitalization is the major drawback, but continued observation and inpatient care may be needed for other indications (e.g. bleeding) in this subset of patients.

CONCLUSIONS

A continuous intravenous infusion of FabAV between 2 and 4 vials per day, titrated to effect, and continued for 6-14 days post-envenomation appeared to be associated with reversal of late hematologic effects of rattlesnake envenomation and, when combined with indicated human blood products, control of significant bleeding. Continuous intravenous infusion of FabAV may be safer, more efficacious, and more cost-effective than observation without FabAV treatment or as-needed bolus dosing in selected patients with late hematologic abnormalities.

The role for coagulation markers in mild snakebite envenomations

Introduction

The majority of patients seeking medical treatment for snakebites do not suffer from severe envenomation. However, no guidelines exist for ordering coagulation markers in patients with minimal or moderate envenomation, nor in those who do not receive antivenom. In this study, we sought to determine whether it was possible to limit the practice of ordering coagulation studies to those patients suffering severe envenomation, rattlesnake envenomation, or both.

Methods

A retrospective chart review was performed on all cases of crotalid snakebite presenting to an adult emergency department (ED) from April 1998 to June 2006. Each chart was abstracted for patient's age, gender, type of snake (if known), severity of envenomation at initial presentation, coagulation test results, whether antivenom was administered, and whether the patient was admitted.

Results

Over an approximately 8-year period, 131 snakebite cases presented that met the inclusion criteria, of which 35 (26.7%) had some type of coagulation marker abnormality. Limiting coagulation testing to patients suffering severe envenomation or rattlesnake envenomation would have resulted in failure to identify 89% or 77%, respectively, of the 35 patients who were found to have at least 1 abnormal coagulation marker.

Conclusion

Our study failed to identify a subset of patients that could be defined as low risk or for whom coagulation marker testing could be foregone. This study suggests that coagulation tests should be routinely performed on all patients presenting to the ED with complaints of envenomation by copperheads, moccasins, or rattlesnakes. Further clarification of when coagulation markers are indicated may require a prospective study that standardizes snake identification and the timing of coagulation marker testing.

Reality bites: a case of severe rattlesnake envenomation

Rattlesnake venoms can cause a wide range of adverse human health effects. However, with the availability of modern antivenin, toxicity can generally be minimized and controlled. We present a rare case of rattlesnake envenomation resulting in severe systemic effects and syndrome relapse. Management considerations and patient course are described in the context of the current literature.

Incidence of immediate hypersensitivity reaction and serum sickness following administration of Crotalidae polyvalent immune Fab antivenom: a meta-analysis

OBJECTIVES

  Crotalidae polyvalent immune Fab (ovine) (FabAV) is commonly used in the treatment of symptomatic North American crotaline snake envenomation. When approved by the U.S. Food and Drug Administration in 2000, the incidences of immediate hypersensitivity reactions and serum sickness were reported as 0.14 and 0.18, respectively. The objective of this meta-analysis was to evaluate the incidence of immediate hypersensitivity reactions and serum sickness reported in studies of patients treated with FabAV therapy after North American crotaline envenomation.

METHODS

  The authors searched PubMed, Ovid MEDLINE, and EMBASE from January 1, 1997, to September 20, 2010, for English-language medical literature and cross-referenced bibliographies of reviewed articles. The published abstracts of the major toxicology conferences were also searched. All prospective and retrospective cohort studies with patients receiving FabAV therapy for North American crotaline envenomations were eligible for data abstraction. Two content experts reviewed full-text articles and extracted relevant study design and outcome data. Proportions of immediate hypersensitivity and serum sickness for each study were analyzed in a random-effects model to produce an overall estimate of immediate hypersensitivity and serum sickness incidence associated with FabAV administration.

RESULTS

  The literature search revealed 11 unique studies of patients who received FabAV that contained information on immediate hypersensitivity reactions and serum sickness. The meta-analysis produced a combined estimate of the incidence of immediate hypersensitivity of 0.08 (95% confidence interval [CI] = 0.05 to 0.11) and a combined estimate of the incidence of serum sickness of 0.13 (95% CI = 0.07 to 0.21).

CONCLUSIONS

  In this systematic literature review and meta-analysis, the combined estimates of the incidence of immediate hypersensitivity reactions and serum sickness from FabAV in the treatment of symptomatic North American crotaline envenomations appear to be lower than previously reported, at 0.08 and 0.13, respectively.

Recurrent, persistent, or late, new-onset hematologic abnormalities in Crotaline snakebite

BACKGROUND. Hematologic effects from rattlesnake envenomation exhibit a phenomenon of recurrent, persistent or late, new onset (late) abnormalities in some Fab antivenom-treated patients 4 or more days post-envenomation. Indicators that reliably identify or exclude those patients at risk of late hematologic effects have not been developed. METHODS. This was a retrospective, observational case series of rattlesnake bite records at two US poison centers. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for D-dimer, fibrinogen, platelets, platelet count trend, INR and PTT associated with late hematologic abnormalities, were determined. RESULTS. Three hundred seventy six cases were reviewed. Sixty cases met inclusion criteria. Overall, 17 of 60 patients (28%) had a hematologic abnormality as a result of envenomation. Eleven of 60 patients (65% of those with a hematologic abnormality; 18% overall) developed late hematologic abnormalities 4 or more days post-envenomation. Four patients had late, new onset hypofibrinogenemia and/or thrombocytopenia. All were associated with early D-dimer elevation and/or platelet rise in response to FabAV treatment, respectively. Normal hematologic parameters in the first 48 h post-envenomation and the lack of a greater than 20% rise in platelets within 4 h post-antivenom administration had a 100% NPV for late hematologic effects. CONCLUSIONS. Patients with early onset hypofibrinogenemia, a positive D-dimer, thrombocytopenia, or a 20% increase in platelet count within 4 h post-treatment had a significant likelihood of late hematologic effects. Patients in whom fibrinogen, D-dimer, INR, PTT, and platelet counts remained normal throughout the first 48 h post-envenomation, and who did not exhibit a >20% increase in platelet count within 4 h post-antivenom administration, did not develop late hematologic effects.

A randomized multicenter trial of Crotalidae polyvalent immune F(ab) antivenom for the treatment of rattlesnake envenomation in dogs

OBJECTIVE

To determine clinical efficacy of the Crotalidae polyvalent immune F(ab) (ovine) antivenom (OPCA) against progressive crotalid envenomation in the dog as reflected in stabilization or improvement of snakebite severity scores (SSS). Additionally, due to the potential decreased half-life of the F(ab) antibodies in dogs we compared SSS between dogs receiving 2 different dosing regimes.

DESIGN

Prospective, clinical trial.

SETTING

Five veterinary emergency and critical care facilities.

ANIMALS

One hundred and fifteen client-owned Crotalid (rattlesnake) snake bitten dogs in whom worsening of the envenomation syndrome was observed before OPCA treatment.

INTERVENTIONS

In a multicenter randomized clinical trial a single dose (1 vial) of OPCA alone was compared with 2 doses (1/2 vial each) administered 6 hours apart. Standard supportive care was provided in all cases.

MEASUREMENTS AND MAIN RESULTS

Data were available for 115 patients, 9 of which were fatalities. All patients' clinical condition was documented with a standardized SSS system accounting for each major body system. Each fatality received maximum severity scores of 20. The mean severity score of the 115 patients decreased from 4.19 to 3.29 points and there was no difference between the 2 treatment groups. The mean severity score of the 107 patients without fatalities decreased from 4.16 to 2.15. Antivenin-related acute reactions occurred in 6 dogs (6%), and no serum sickness occurred within the 95 cases contacted at the 2-week posttreatment follow-up.

CONCLUSIONS

In the first randomized trial in dogs of antivenin in the United States, OPCA effectively stabilized or terminated venom effects. There were no statistical differences detected between treatment groups within the study time frame.

Unified treatment algorithm for the management of crotaline snakebite in the United States: results of an evidence-informed consensus workshop

BACKGROUND

Envenomation by crotaline snakes (rattlesnake, cottonmouth, copperhead) is a complex, potentially lethal condition affecting thousands of people in the United States each year. Treatment of crotaline envenomation is not standardized, and significant variation in practice exists.

METHODS

A geographically diverse panel of experts was convened for the purpose of deriving an evidence-informed unified treatment algorithm. Research staff analyzed the extant medical literature and performed targeted analyses of existing databases to inform specific clinical decisions. A trained external facilitator used modified Delphi and structured consensus methodology to achieve consensus on the final treatment algorithm.

RESULTS

A unified treatment algorithm was produced and endorsed by all nine expert panel members. This algorithm provides guidance about clinical and laboratory observations, indications for and dosing of antivenom, adjunctive therapies, post-stabilization care, and management of complications from envenomation and therapy.

CONCLUSIONS

Clinical manifestations and ideal treatment of crotaline snakebite differ greatly, and can result in severe complications. Using a modified Delphi method, we provide evidence-informed treatment guidelines in an attempt to reduce variation in care and possibly improve clinical outcomes.

Factors associated with difficulty achieving initial control with crotalidae polyvalent immune fab antivenom in snakebite patients

BACKGROUND

The prescribing information for Crotalidae Fab antivenom (FabAV) instructs clinicians to administer FabAV until initial control of the envenomation syndrome is achieved. Risk factors for difficulty achieving initial control are not known.

OBJECTIVES

The study aim was to identify factors present before administration of antivenom associated with difficulty achieving initial control.

METHODS

The authors conducted a retrospective study of all patients presenting to any one of 17 centers and receiving FabAV from 2002 to 2004. Demographic and historical information, as well as data about nine specific venom effects, were collected prior to the administration of antivenom. An expert panel used standard criteria to determine if initial control was achieved. The patient group that had difficulty achieving initial control was compared to the group that achieved initial control, and adjusted odds ratios were calculated using stepwise logistic regression.

RESULTS

A total of 247 patients were included in the final analysis. The majority of patients were envenomated on the upper extremity and were young males. A total of 203 patients (82.2%) achieved initial control. In univariate analysis, thrombocytopenia, bleeding, neurologic effects, and a severe bite were significantly associated with difficulty achieving initial control. After logistic regression, the presence of neurologic effects and thrombocytopenia remained significantly associated with difficulty achieving initial control. When both factors were present, the patient was 13.8 times more likely to have difficulty achieving initial control.

CONCLUSIONS

A number of factors were present before the administration of FabAV that were independently associated with difficulty achieving initial control of the envenomation syndrome. Predicting which patients will have difficulty achieving initial control has important ramifications for patient disposition and may provide insight into the mechanisms for lack of antivenom efficacy.

Late hematologic toxicity following treatment of rattlesnake envenomation with crotalidae polyvalent immune Fab antivenom

BACKGROUND

North American rattlesnake envenomations commonly produce defibrination, coagulopathy and/or thrombocytopenia, which may be reversed following treatment with Crotalidae Polyvalent Immune Fab Ovine (FabAV). Despite initial resolution with FabAV, late onset or recurrence of venom-induced hematologic effects may occur. Time at which onset of late hematotoxicity may first be detected is unknown. The purpose of this study was to identify the incidence and time of onset of recurrent or new late hypofibrinogenemia, coagulopathy, or thrombocytopenia in a cohort of rattlesnake envenomation patients seen in outpatient follow-up after treatment with FabAV, and to report hematologic outcomes in these patients.

METHODS

Review of 66 charts of patients with rattlesnake envenomation who were treated with FabAV, and subsequently had outpatient follow-up evaluation at least 48 h after last FabAV, was performed. Demographic information, rattlesnake and bite characteristics, dose and timing of antivenom administration, adverse events, in-patient laboratory values, length of hospital stay, and follow-up laboratory values were collected. The primary outcome parameters were recurrent or delayed onset coagulopathy, hypofibrinogenemia, or thrombocytopenia identified no sooner than 48 h after last dose of FabAV.

RESULTS

Prior to control of the envenomation with FabAV, 42 patients (63.6%) experienced hematologic toxicity. At follow-up, 21 patients (32%) were found to have late coagulopathy, hypofibrinogenemia, or thrombocytopenia. Of twenty-three patients (35%) with more than one follow-up visit, fifteen had normal laboratory findings at the first follow-up visit. Five of these 15 patients (8% of total study group; 33% of this subgroup) with normal hematologic studies at first follow-up exhibited late hematologic toxicity at second follow-up. Severe late hematologic toxicity developed in five of 66 (8%) patients. One patient was retreated with FabAV for late severe thrombocytopenia.

CONCLUSION

Recurrent and delayed onset of hematologic toxicity in rattlesnake envenomation victims treated with FabAV is common. Follow-up more than three days after treatment is necessary to detect all cases of late hematologic toxicity.

Recurrent coagulopathy and thrombocytopenia in children treated with crotalidae polyvalent immune fab: a case series

OBJECTIVES

Recurrent signs and symptoms after initial treatment and control of coagulopathy and thrombocytopenia after American pit viper (crotaline) envenomations have been previously described in patients treated with Crotalidae polyvalent immune Fab antivenom (FabAV). The significance and necessity of treatment of these recurrent abnormalities are uncertain. Our goal was to further characterize recurrent coagulopathy or thrombocytopenia in pediatric patients.

METHODS

All cases presenting to our Toxicology Consult Service, which covers 6 hospitals in a metropolitan area, from May 2007 to April 2008 with recurrent coagulopathy after initial control with FabAV were included and retrospectively reviewed.

RESULTS

Four cases of pediatric patients are presented who presented with recurrent coagulopathy and/or thrombocytopenia after initial control with FabAV. The patients were all treated with delayed administration of FabAV with variable results. Blood products administered without concurrent FabAV were of limited use. The laboratory abnormalities took up to 18 days to resolve in one case. One patient developed hemodynamically significant spontaneous bleeding.

CONCLUSIONS

The cases presented here suggest administration of FabAV may correct delayed coagulopathy associated with crotaline envenomations. The first 3 cases illustrate that in the face of severe derangements in laboratory values, most envenomated patients treated with FabAV do not develop significant bleeding. These cases may respond to additional antivenom alone. However, case 4 illustrates that hemodynamically significant spontaneous bleeding can occur. Until more data are available, readministration of FabAV is a reasonable first-line therapy for delayed coagulopathy associated with crotaline envenomations.

Randomised controlled double-blind non-inferiority trial of two antivenoms for saw-scaled or carpet viper (Echis ocellatus) envenoming in Nigeria

BACKGROUND

In West Africa, envenoming by saw-scaled or carpet vipers (Echis ocellatus) causes great morbidity and mortality, but there is a crisis in supply of effective and affordable antivenom (ISRCTN01257358).

METHODS

In a randomised, double-blind, controlled, non-inferiority trial, "EchiTAb Plus-ICP" (ET-Plus) equine antivenom made by Instituto Clodomiro Picado was compared to "EchiTAb G" (ET-G) ovine antivenom made by MicroPharm, which is the standard of care in Nigeria and was developed from the original EchiTAb-Fab introduced in 1998. Both are caprylic acid purified whole IgG antivenoms. ET-G is monospecific for Echis ocellatus antivenom (initial dose 1 vial) and ET-Plus is polyspecific for E. ocellatus, Naja nigricollis and Bitis arietans (initial dose 3 vials). Both had been screened by pre-clinical and preliminary clinical dose-finding and safety studies. Patients who presented with incoagulable blood, indicative of systemic envenoming by E. ocellatus, were recruited in Kaltungo, north-eastern Nigeria. Those eligible and consenting were randomly allocated with equal probability to receive ET-Plus or ET-G. The primary outcome was permanent restoration of blood coagulability 6 hours after the start of treatment, assessed by a simple whole blood clotting test repeated 6, 12, 18, 24 and 48 hr after treatment. Secondary (safety) outcomes were the incidences of anaphylactic, pyrogenic and late serum sickness-type antivenom reactions.

FINDINGS

Initial doses permanently restored blood coagulability at 6 hours in 161/194 (83.0%) of ET-Plus and 156/206 (75.7%) of ET-G treated patients (Relative Risk [RR] 1.10 one-sided 95% CI lower limit 1.01; P = 0.05). ET-Plus caused early reactions on more occasions than did ET-G [50/194 (25.8%) and 39/206 (18.9%) respectively RR (1.36 one-sided 95% CI 1.86 upper limit; P = 0.06). These reactions were classified as severe in 21 (10.8%) and 11 (5.3%) of patients, respectively.

CONCLUSION

At these doses, ET-Plus was slightly more effective but ET-G was slightly safer. Both are recommended for treating E. ocellatus envenoming in Nigeria.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN01257358.

Snake bite

Snake bite is a common and frequently devastating environmental and occupational disease, especially in rural areas of tropical developing countries. Its public health importance has been largely ignored by medical science. Snake venoms are rich in protein and peptide toxins that have specificity for a wide range of tissue receptors, making them clinically challenging and scientifically fascinating, especially for drug design. Although the full burden of human suffering attributable to snake bite remains obscure, hundreds of thousands of people are known to be envenomed and tens of thousands are killed or maimed by snakes every year. Preventive efforts should be aimed towards education of affected communities to use proper footwear and to reduce the risk of contact with snakes to a minimum through understanding of snakes' behaviour. To treat envenoming, the production and clinical use of antivenom must be improved. Increased collaboration between clinicians, epidemiologists, and laboratory toxinologists should enhance the understanding and treatment of envenoming.

Recurrent coagulopathy with delayed significant bleeding after crotaline envenomation

OBJECTIVES

Report of delayed significant coagulopathy, thrombocytopenia, and bleeding after Crotaline envenomation.

METHODS

Recurrent coagulopathy and thrombocytopenia have been described after treatment of Crotaline envenomation with Crotalidae polyvalent immune Fab (CroFab). Until now, there have been no reports of significant spontaneous bleeding despite these abnormalities.

RESULTS

Crotalidae polyvalent immune Fab has a relatively short half-life compared with previous antivenoms used to treat snake bite. This shorter half-life allows for recurrence of venom effects. Therefore, patients with Crotaline envenomation should undergo close monitoring for recurrence of coagulopathy or thrombocytopenia after treatment with CroFab.

CONCLUSIONS

If coagulopathy or thrombocytopenia recurs, retreatment with CroFab should be considered to prevent significant bleeding.

AAPCC database characterization of native U.S. venomous snake exposures, 2001-2005

BACKGROUND

Differences in victim demographics, clinical effects, managements, and outcomes among native viperid (rattlesnake, copperhead, and cottonmouth) and elapid (coral snake) species have not been systematically characterized.

METHODS

The database of the American Association of Poison Control Centers from 2001 through 2005 was analyzed.

RESULTS

Between 2001 and 2005, there were 23,676 human exposures (average = 4,735/year) to native venomous snakes in the United States reported to U.S. poison centers in all states except Hawaii: 98% were to viperid snakes and 2% to elapids. Overall, 77% of victims were male, 70% were adults >20 years, and 12% were aged less than 10 years. Sixty-five cases involved pregnant women, with rattlesnake bites resulting in moderate or greater effects in over 70%. The overall hospital admission rate was 53%. Outcomes were generally more severe with rattlesnake and copperhead envenomations and in children <6 years of age. The fatality rate of reported cases was 0.06%.

CONCLUSIONS

Native U.S. venomous snakebite results in considerable morbidity and mortality. Rattlesnake and copperhead envenomations, and those in children <6 years of age, produce the most severe outcomes, but coral snakebites result in similar hospital admission rates.

Crotaline Fab antivenom appears to be effective in cases of severe North American pit viper envenomation: an integrative review

Background

In 2000, the United States Food and Drug Administration approved Crotalidae Polyvalent Immune Fab (Ovine) (hereafter, FabAV), "for the management of patients with minimal to moderate North American Crotalid envenomation." Because whole-IgG pit viper antivenom is no longer available in the United States, FabAV is currently the only specific treatment option available to United States clinicians treating snakebite victims of any severity. No clinical trial data are available concerning the effectiveness of FabAV for treatment of severe snakebite, but several published articles describe its use in this setting.

Methods

We performed a comprehensive review of the English-language medical literature to identify all publications (1996 to July, 2008) containing data about the administration of FabAV. Two trained reviewers separately extracted case-level data concerning the administration of FabAV to patients with severe envenomation by North American crotaline snakes to a standardized form. Descriptive statistics were used. In addition, we hand-searched the US National Poison Data System reports for the years 2000–2006 to identify and describe any reports of death that occurred after FabAV administration.

Results

The literature review found 147 unique publications regarding FabAV. Twenty-four evaluable cases of severe human envenomation treated with FabAV were identified in 19 publications. Seven cases were described in five cohort studies, and 17 cases were described in 14 single patient case reports or non-cohort case series. Sixty-five specific severe venom effects were reported in these 24 patients, of which 50 effects (77%) improved or resolved after FabAV therapy. Initial control of all severe venom effects was achieved in 12 patients (50%). The rate at which initial control was achieved was significantly higher among patients reported in the cohort series than in the case series and non-cohort reports (100% vs. 29%, P = 0.005). The median dose of FabAV used to obtain initial control was 6 vials (range: 4 – 18 vials). Nine patients had severe venom effects that persisted despite FabAV therapy. Recurrent and/or delayed-onset severe defibrination syndrome occurred in 12 patients, most of whom did not receive recommended maintenance FabAV dosing. No patient developed systemic bleeding.

Conclusion

In this structured literature review, FabAV appears to be effective in the management of severe crotaline snake envenomation. Incomplete response to therapy, recurrence of venom effects, and delayed-onset venom effects were reported in case reports, but not reported in cohort studies.

Crotalidae polyvalent immune Fab for the treatment of pediatric crotaline envenomation

Crotaline snakebites occur frequently in children, often resulting in significant morbidity. Crotalidae Polyvalent Immune Fab antivenom (FabAV) became available for clinical use in the US in 2000 and is currently the standard of care for the treatment of crotaline envenomation. The pediatric emergency care provider should be familiar with FabAV because its judicious use in affected children can greatly decrease morbidity caused by crotaline snakebites. This article will review the use of FabAV for the treatment of pediatric crotaline envenomation.

The management of pit viper envenomation of the hand

Snakebites are common among the rural population of developing countries. The severity of venomous snakebites depends on several factors, including the location of the bite, the amount of venom injected, and the effectiveness of the initial therapy. Snakebites frequently occur in the extremities with approximately two thirds of envenomations occurring in the upper extremities. In this study, we presented 12 cases of hand reconstruction after Vipera snakebites and discussed how to minimize functional loss and maximize hand rehabilitation. Twelve patients bitten by Vipera between 2001 and 2006 were included in this study. Groin flaps were performed in three cases, full-thickness grafts in two cases, thenar flaps in three cases, and cross finger flaps in three cases. With medical management, spontaneous healing occurred in one case. We prefer to use flaps on the volar site of the hand and, if the bone is not exposed, full-thickness grafts on the dorsal site of the hand. We also recommend starting rehabilitation of the hand early.

Fatality in a case of envenomation by Crotalus adamanteus initially successfully treated with polyvalent ovine antivenom followed by recurrence of defibrinogenation syndrome

INTRODUCTION

Recurrences of clinical or laboratory manifestations of North American pit viper envenomation may happen despite control of the envenomation syndrome by prompt and adequate antivenom therapy. Recurrences of coagulopathy in victims of Eastern diamondback rattlesnake envenomation are generally regarded as benign. The vast majority suffer no actual bleeding despite florid coagulation laboratory abnormalities due to selective defibrinogenation.

CASE REPORT

We report what we believe to be the first fatality following successful control of the envenomation syndrome following ovine antivenom treatment resulting from envenomation by a bite from the Eastern diamondback rattlesnake. This case raises the question of whether such recurrences are in fact benign, causal, or coincidental. This patient sustained significant brain hemorrhage and death ensued due to generalized cerebral edema. Defibrinogenation occurred 4 days after treatment with ovine antivenom.

DISCUSSION

Coagulation abnormalities following Eastern diamondback rattlesnake envenomation are due to selective defibrinogenation. This is separate from disseminated intravascular coagulation (DIC). Thrombin generation, thus hemostasis, are generally considered normal. This case may cause reexamination of this belief.

Stroke and snakebite: case report

Snakebites are common and lead to potential complications like neuromyopathies and strokes, these last associated with disturbances of blood coagulation. We report on a 65 years old woman of cerebral intraparenchymal hemorrhage associated with snakebite by a Bothrops jararaca that occurred in the Reconcavo of Bahia, BA, Brazil. The patient was submitted to a surgical evacuation of the hematoma, with a good result. This report is accompanied by a revision about the association among snakebite and neurological complications, emphasizing strokes. Statistics reveal a high incidence of snakebite in the world, mainly in tropical countries and gets attention for his socioeconomic impact. The clinical and laboratory characteristics to identify the victims that present a high risk of presenting strokes are discussed in order to identify early those patients, so that they may be treated in a more precocious and effective way.

Toxic Exposure Surveillance System (TESS)-based characterization of U.S. non-native venomous snake exposures, 1995-2004

BACKGROUND

Non-native (exotic) snake exposures in the United States have not been systematically characterized.

METHODS

The Toxic Exposure Surveillance System (TESS) database of the American Association of Poison Control Centers was analyzed to quantify the number and types, demographic associations, clinical presentations, managements and outcomes, and the health resource utilization of non-native snake exposures.

RESULTS

From 1995 through 2004, there were 399 non-native exposures in the TESS database. Of these, 350 snakes (87%) were identified by genus and species, comprising at least 77 different varieties. Roughly equal percentages of snakes originated in Asia, Africa and Latin America, with a smaller number from the Middle-East, Australia, and Europe. Nearly half were viperids and a little more than a third were elapids. The vast majority of exposed individuals were adults. However, almost 15% were aged 17 years or less, and almost 7% were children aged 5 years or younger. Eighty-four percent were males. The vast majority of exposures occurred at the victim's own residence. Over 50% were evaluated at a healthcare facility, with 28.7% admitted to an ICU. Overall, 26% of patients were coded as receiving antivenom treatment. Coded outcomes were similar between viperid and elapid envenomations. There were three deaths, two involving viperid snakes and one elapid. Enhancements to the TESS database are required for better precision in and more complete characterization of non-native snake envenomations.

Pharmacokinetics of a F(ab')2 scorpion antivenom in healthy human volunteers

This paper presents the first study of F(ab')2 scorpion antivenom pharmacokinetics in humans. We have studied the pharmacokinetics of an antiscorpion venom preparation (Alacramyn) in eight human healthy volunteers. The fabotherapic was administered as a 47.5 mg i.v. bolus. Blood samples were drawn at 0, 5, 15, 30, 45, 60, 90, 120, 180 and 360 min after antivenom administration. Subsequently, the volunteers made seven visits to the hospital. Four of them at 24 h intervals, one at day 10, and one at day 21. We measured antivenom plasmatic concentrations using a specific high sensitivity ELISA method for F(ab')2. The time course of F(ab')2 in serum of seven subjects was well described by a lineal combination of three exponential components; a four exponential component model was necessary to fit the eighth subject. The most significant antivenom pharmacokinetic parameters determined were: AUC(infinity)=596.9 (369.3, 891.2) mg h l(-1); V(c) = 3.1 (2.3, 4.3)l; V(ss) = 15.4 (12.8, 39.9)l; MRT = 250.0 (218.8, 310.2) h; CL = 96.6 (58.0, 139.2) ml h(-1); t(1/2,tau1) (also called t(1/2,alpha)) = 0.25 (0.13, 0.37) h; t(1/2,tau(z)) (corresponding to the slowest component) = 161.3 (141.0, 212.0) h.

Treatment of US Crotalidae Bites

In the US, two antivenins are marketed for the treatment of snake envenomation. The horse-derived serum-globulin-based Antivenin (Crotalidae) Polyvalent (ACP) has been available since 1954. There are few data on the efficacy and incidence of adverse events that occur following the administration of ACP. Most of the data are retrospective, anecdotal, or case reports. In 2000, ovine-derived serum-globulin-based ACP (Crofab) became available. Crofab is said to cause fewer reactions than ACP, but there are few comparative data to substantiate this claim. Although both antivenins ameliorate the systemic symptoms following snake envenomation, the efficacy of either antivenin in decreasing oedema and swelling is unknown for a number of reasons. Clinical trials are small and have not included control arms. The degree of oedema, as well as the efficacy of the antivenin in decreasing oedema, may depend on the genera of the snake (usually unknown) that envenomated the patient. This article compares available data on clinical aspects of the two antivenins. More prospective data are needed to determine the comparative efficacy of the two antivenins, or the efficacy of Crofab in preventing tissue oedema. There are still unanswered questions regarding the optimal dosing regimen of Crofab.

Pharmacokinetic-pharmacodynamic relationships of immunoglobulin therapy for envenomation

Parenteral administration of horse- and sheep-derived antivenoms constitutes the cornerstone in the therapy of envenomations induced by animal bites and stings. Depending on the type of neutralising molecule, antivenoms are made of: (i) whole IgG molecules (150 kDa), (ii) F(ab')(2) immunoglobulin fragments (100 kDa) or (iii) Fab immunoglobulin fragments (50 kDa). Because of their variable molecular mass, these three types of antivenoms have different pharmacokinetic profiles. Fab fragments have the largest volume of distribution and readily reach extravascular compartments. They are catabolised mainly by the kidney, having a more rapid clearance than F(ab')(2) fragments and IgG. On the other hand, IgG molecules have a lower volume of distribution and a longer elimination half-life, showing the highest cycling through the interstitial spaces in the body. IgG elimination occurs mainly by extrarenal mechanisms. F(ab')(2) fragments display a pharmacokinetic profile intermediate between those of Fab fragments and IgG molecules. Such diverse pharmacokinetic properties have implications for the pharmacodynamics of these immunobiologicals, since a pronounced mismatch has been described between the pharmacokinetics of venoms and antivenoms. Some venoms, such as those of scorpions and elapid snakes, are rich in low-molecular-mass neurotoxins of high diffusibility and large volume of distribution that reach their tissue targets rapidly after injection. In contrast, venoms rich in high-molecular-mass toxins, such as those of viperid snakes, have a pharmacokinetic profile characterised by a rapid initial absorption followed by a slow absorption process from the site of venom injection. Such delayed absorption has been linked with recurrence of envenomation when antibody levels in blood decrease. This heterogeneity in pharmacokinetics and mechanism of action of venom components requires a detailed analysis of each venom-antivenom system in order to determine the most appropriate type of neutralising molecule for each particular venom. Besides having a high affinity for toxicologically relevant venom components, an ideal antivenom should possess a volume of distribution as similar as possible to that of the toxins being neutralised. Moreover, high levels of neutralising antibodies should remain in blood for a relatively prolonged time to assure neutralisation of toxins reaching the bloodstream later in the course of envenomation, and to promote redistribution of toxins from extravascular compartments to blood. Additional studies are required on different venoms and antivenoms in order to further understand the pharmacokinetic-pharmacodynamic relationships of antibodies and their fragments and to optimise the immunotherapy of envenomations.

Preclinical assessment of the ability of polyvalent (Crotalinae) and anticoral (Elapidae) antivenoms produced in Costa Rica to neutralize the venoms of North American snakes

Polyvalent (Crotalinae) and anticoral (Elapidae) antivenoms produced by Instituto Clodomiro Picado, Costa Rica, were assessed for their ability to neutralize various toxic activities of the venoms of North American snakes of the genera Crotalus, Agkistrodon and Micrurus, in assays involving preincubation of venom and antivenom. When the intraperitoneal route of injection was utilized, polyvalent (Crotalinae) antivenom was effective in the neutralization of the venoms of Crotalus atrox, Crotalus adamanteus, Crotalus viridis viridis, Crotalus horridus atricaudatus, Agkistrodon contortrix contortrix and Agkistrodon piscivorus piscivorus, whereas the venom of Crotalus scutulatus was not neutralized. When the intravenous route was used, results differed depending on the "challenge dose" of venom employed. Polyvalent antivenom neutralized all venoms when mice were challenged with 2 LD(50)s of venom. When 5 LD(50)s were used, antivenom neutralized the venoms of C. atrox, C. adamanteus, C. v. viridis and C. h. atricaudatus, being ineffective in the neutralization of C. scutulatus, A. c. contortrix and A. p. piscivorus. Polyvalent antivenom was effective in the neutralization of hemorrhagic and myotoxic activities of all venoms studied. It also neutralized coagulant activity of C. adamanteus venom, whereas most of the venoms were devoid of clotting activity on plasma in vitro. Moreover, it neutralized defibrinating activity of the only three venoms that induced this effect (i.e. C. adamanteus, A. c. contortrix and A. p. piscivorus). Anticoral (Elapidae) antivenom neutralized lethality induced by the venom of Micrurus fulvius, using either the intravenous or the intraperitoneal routes of injection. Moreover, it neutralized myotoxic effect of this venom as well. It is concluded that polyvalent antivenom neutralizes lethality and other activities of most of the crotaline venoms tested. However, since it is ineffective in neutralizing the lethal effect of C. scutulatus venom, it is suggested that a venom containing presynaptically-active neurotoxic phospholipases A(2) related to "mojave toxin" needs to be introduced in the immunizing mixture in order to increase the neutralizing scope of this product in North America. Anticoral antivenom is highly effective in the neutralization of the venom of M. fulvius.

Persistent coagulopathy in snake bite

Bleeding diathesis is a cardinal feature of viperine bite, which has been thought to last not more than 24 hours. There is scarcity of literature about prolonged bleeding disorder in snake envenomation. Various explanations suggested in the literature include-temporary decrease in antivenin levels, rapid elimination of antivenin from circulation or continuous release of unneutralised venom from the envenomated site. Two children with prolonged coagulopathy lasting for more than a week, correction of which required more than 300 ml of antisnake venom are reported here.

Biphasic rattlesnake venom-induced thrombocytopenia

Thrombocytopenia is a common occurrence in moderate to severe crotaline envenomation. The exact mechanism by which rattlesnake venom leads to thrombocytopenia is unclear, but aggressive treatment with crotaline-specific antivenom often leads to resolution of this disorder. Crotalinae Polyvalent Immune Fab (CroFab(TM), Protherics Inc., Nashville, TN) (crotaline Fab) is now available for the treatment of symptomatic rattlesnake envenomation. Although recurrence of thrombocytopenia has been reported in patients after envenomation treated with crotaline Fab, cases refractory to this therapy have not been described. We report a case of severe crotaline envenomation that appears to have exhibited two separate episodes of thrombocytopenia, only one of which responded to antivenom. The second, later phase was refractory to both crotaline Fab as well as traditional Antivenin (Crotalinae) Polyvalent (Wyeth-Ayerst Pharmaceuticals, Philadelphia, PA) (ACP). By reviewing the literature regarding venom-induced thrombocytopenia, we attempt to explain this "biphasic" phenomenon and the inability of crotaline Fab to reverse this toxic effect.

The efficacy of two antivenoms against the venom of North American snakes

Mortality due to snake envenomation is not a major problem in the United States with approximately 8-12 deaths per year, but envenomation is a serious problem that can result in functional disability, loss of extremities, and a costly recovery. Physicians encounter different clinical situations with each new snakebite victim because of the geographical variations in snake venoms. The best and most acceptable form of treatment is the use of antivenom; however, it must be administered as soon as possible since it is not so effective at reducing local signs of envenomation such as necrosis. The antivenom in the United States is in short supply, expensive and may not even be the most effective for neutralizing all North American snake venoms. In this study, we tested two antivenoms. The first was a Crotalidae Polyvalent Fab fragment with Ovine origin (FabO) manufactured in London, and the second was Antivipmyn, a Mexican manufactured antivenom that is F(ab')(2) fragment produced in horse (Fab(2)H). The efficacy of the two antivenoms was tested with 15 different snake venoms found in North America. Three different assays were used to test the efficacy of the antivenoms, the in vivo serum protection test (ED(50)), antihemorrhagic and anticoagulant. The Fab(2)H antivenom was most effective in neutralizing the hemorrhagic activity of 78% of the hemorrhagic venoms used in this study. In the ED(50) assay, the Fab(2)H antivenom was effective in neutralizing all venoms used in this study, while FabO neutralized all but C. m. molossus venom. However, in most cases, FabO required less antivenom than Fab(2)H antivenom to neutralize three LD(50).

Crotaline Fab antivenom for the treatment of children with rattlesnake envenomation

OBJECTIVE

There is little data regarding safety or efficacy of Crotalinae polyvalent immune Fab (ovine) antivenom (crotaline Fab) in pediatric patients. Our objective was to provide the first information regarding safety and effectiveness of this new drug in children.

METHODS

Data were collected prospectively and retrospectively for all consecutive pediatric patients bitten by rattlesnakes and treated at 2 urban hospitals during 2001. Cases were included if there were signs of envenomation at presentation, patient age was 13 years or less, and there was administration of crotaline Fab. Cases were excluded if antivenin (Crotalidae) polyvalent (equine origin, the conventional antivenom) was given. Primary outcome variables were snakebite severity scores throughout the course of therapy, number of vials of crotaline Fab administered, occurrence of allergic reactions, adjunct surgical therapy, and the presence of permanent sequelae or serum sickness identified at follow-up.

RESULTS

In the 12 cases studied, ages ranged from 14 months to 13 years (mean: 6.9; standard deviation: 4.2). Presentation snakebite severity scores ranged from 2 to 9 (mean: 5.3; standard deviation: 2.3). Total crotaline Fab doses ranged from 4 to 22 vials (mean: 12.7; standard deviation: 5.4). Initial control of symptoms was achieved with 4 to 16 vials (mean: 7.7; standard deviation: 3.7), and severity scores stabilized or improved within 24 hours in all patients. Recurrence of local swelling occurred in 1 case despite scheduled repeat doses of antivenom. No cases required surgical intervention, and no permanent sequelae were identified. No immediate or delayed hypersensitivity reactions occurred.

CONCLUSION

In this group of pediatric patients treated for rattlesnake envenomation, crotaline Fab antivenom was safe and seemed to be effective.

Recurrence phenomena after immunoglobulin therapy for snake envenomations: Part 2. Guidelines for clinical management with crotaline Fab antivenom

Recurrent local and coagulopathic effects (worsening after clinical improvement) have been described after treatment with Fab antivenom for envenomation by North American crotaline snakes. Although similar phenomena have been described previously in snakebite, few studies have examined recurrence or its management. Recurrence is consistent with known venom and antivenom kinetics and dynamics. The clinical significance of late coagulopathy after snakebite is uncertain, but clinically significant bleeding is a possibility. Prevention and treatment of recurrence with Fab antivenom require repeated dosing for at least 18 hours, with close monitoring of at-risk patients in the follow-up period. Duration of therapy depends on individual risk factors and coagulation response.

Recurrence phenomena after immunoglobulin therapy for snake envenomations: Part 1. Pharmacokinetics and pharmacodynamics of immunoglobulin antivenoms and related antibodies

The production of immunoglobulin antivenoms has evolved over the past 50 years, resulting in a choice of source animals and highly purified, target-specific immunoglobulin fragments (IgG, Fab2, and Fab). Differences in pharmacokinetic and pharmacodynamic properties of these fragments may affect clinical efficacy. For example, both local and systemic recurrences (worsening after initial improvement) with intact or fragmented immunoglobulin antivenoms have been observed. Local recurrence may result in greater tissue injury, and coagulopathic recurrence may result in the risk of hemorrhage. The latter is of particular concern because coagulopathic recurrence usually occurs after patient discharge. Similar phenomena of symptom recurrence have been observed with ovine, digoxin-specific Fab, and with Fab2 and IgG antivenoms from a variety of source animals as well. Recurrence of venom effects in Fab-treated patients appears to be the result of a pharmacokinetic and pharmacodynamic mismatch between the antivenom and target venom components. That is, tissue penetration and venom neutralization is incomplete, and clearance of unbound antivenom (antivenom that has not bound its venom target) is significantly faster than the clearance of some venom components, allowing signs and symptoms of envenomation to recur. Understanding the relative kinetics and dynamics of immunoglobulins and their targets may allow the physician to anticipate their clinical implications and may suggest modifications of the drug or dose to produce better clinical results.

Rattlesnake venom-induced thrombocytopenia response to Antivenin (Crotalidae) Polyvalent: a case series

OBJECTIVE

To test the hypothesis that rattlesnake venom-induced thrombocytopenia would improve following Antivenin (Crotalidae) Polyvalent administration, and that the degree of platelet increase would correlate with the dosage of antivenom.

METHODS

The authors conducted a retrospective review of all patients admitted for rattlesnake envenomation at two southern California hospitals between 1980 and 1998. Patients were included if platelet count was less than 150 x 10(9)/L following a rattlesnake bite. Patients were excluded if they received platelet transfusion. The relationship between Antivenin (Crotalidae) Polyvalent administration and venom-induced thrombocytopenia was evaluated by linear regression and paired t-test.

RESULTS

The authors identified 103 cases of rattlesnake envenomation. Seventeen cases met inclusion criteria for thrombocytopenia. Two patients were excluded because they received platelet transfusions. One additional patient was excluded from paired t-test only because no antivenom was given. Thrombocytopenia usually improved between presentation and discharge (mean difference, 44 x 10(9)/L), although complete resolution was often not achieved. A statistically significant partial improvement in platelet counts immediately after antivenom administration was observed in a subset of patients with severe thrombocytopenia (platelet count <100 x 10(9)/L) (mean difference, 64 x 10(9)/L). Using regression analysis, the authors did not detect a linear relationship 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 improvement 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.

Envenomations

Envenomations are uncommon, challenging causes of critical care admissions. This article describes the diagnosis and treatment of envenomations that cause the most critical care admissions in the United States. Most are caused by the following animals: rattlesnakes, copperheads, cottonmouths, coral snakes, brown recluse spiders, and bark scorpions.