Methodology of clinical studies dealing with the treatment of envenomation

Real life condition evaluation of Inoserp PAN-AFRICA antivenom effectiveness in Cameroon

BACKGROUND

Snakebites is a serious public health issue but remains a neglected tropical disease. Data on antivenom effectiveness are urgently needed in Africa. We assessed effectiveness of Inoserp PAN-AFRICA (IPA), the recommended antivenom available in Cameroon.

METHODOLOGY/PRINCIPAL FINDINGS

We enrolled 447 patients presenting with snakebite in 14 health facilities across Cameroon. At presentation, cytotoxicity, coagulation troubles and neurotoxicity were graded. We administered two to four vials of antivenom to patients based on hemotoxic or neurotoxic signs. We renewed antivenom administration to patients with persistence of bleedings or neurotoxicity 2 hours after each injection. We defined early improvement as a reduction of the grade of envenomation symptoms 2 hours after first injection. Medium-term effectiveness was investigated looking at disappearance of symptoms during hospitalization. After hospital discharge, a home visit was planned to assess long-term outcomes. Between October 2019 and May 2021, we enrolled 447 (93.7%), including 72% from the savannah regions. The median [IQR] age was 25 [14-40]. Envenomation was diagnosed in 369 (82.6%) participants. The antivenom was administered to 356 patients (96.5%) of whom 256 (71.9%) received one administration. Among these patients, cytotoxic symptoms were observed in 336 (94.4%) participants, coagulation disorders in 234 (65.7%) participants and neurotoxicity in 23 (6.5%) participants. Two hours after the first administration of antivenom, we observed a decrease in coagulation disorders or neurotoxicity in 75.2% and 39.1% of patients, respectively. Complete cessation of bleedings and neurotoxicity occurred in 96% and 93% of patients within 24 hours, respectively. Sequelae have been observed in 9 (3%) patients at the home visit 15 days after hospital admission and 11 (3%) died including one before antivenom injection.

CONCLUSIONS/SIGNIFICANCE

We confirmed good effectiveness of the IPA and highlighted the rapid improvement in bleeding or neurotoxicity after the first administration. Sequential administrations of low doses of antivenom, rigorously assessed at short intervals for an eventual renewal, can preserve patient safety and save antivenom.

TRIAL REGISTRATION

NCT03326492.

Hydrocortisone for Preventing Adverse Drug Reactions to Snake Antivenom: A Meta-Analysis

Objective

Pretreatment with hydrocortisone (prehydrocortisone) has been used to protect against adverse drug reactions (ADRs) following antivenom administration after snakebite. However, controversial results have been reported in studies evaluating its efficacy. Herein, we conducted a meta-analysis to evaluate the effect of prehydrocortisone on the risk of ADRs.

Methods

We conducted a systematic search of PubMed, Embase, and Cochrane for relevant studies on the literature published up to December 6, 2020, with no language restrictions. Premedications, including hydrocortisone with or without other drugs, were compared with placebo or no premedication. Our primary end point was the risk of ADRs, which was reported as the number of patients who developed ADRs divided by the total number of snakebite patients administered with antivenom separately for the prehydrocortisone and control groups for each study. We evaluated pooled data using of a random-effects model.

Results

Among 831 identified studies, 4 were eligible and included in our analysis (N = 1348 participants). Upon combining all eight comparisons from the four selected studies, the overall pooled odds ratio (OR) for ADRs was 0.47 (95% CI 0.19, 1.17; p=0.11; I² = 68%). When the analysis was restricted to only articles using hydrocortisone with other drugs, the pooled OR was 0.19 (95% CI 0.05, 0.75; p=0.02; I² = 55%). The result was not statistically significant when the analysis was restricted to studies using prehydrocortisone alone, or randomized controlled designs, or cohorts. Our study was limited by heterogeneity, quality, and a paucity of data.

Conclusions

The findings in this study revealed that prehydrocortisone alone was ineffective. However, the substantial beneficial effect of prehydrocortisone combinations with premedications (injectable antihistamines or adrenaline) used against ADRs cannot be excluded. Therefore, the use of prehydrocortisone combinations with premedications (injectable antihistamines or adrenaline) as a prophylaxis may reduce the ADRs to antivenom.

Antivenom: An immunotherapy for the treatment of snakebite envenoming in sub-Saharan Africa

Snakebite envenoming (SBE) leads to significant morbidity and mortality, resulting in over 90,000 deaths and approximately 400,000 amputations annually. In sub-Saharan Africa (SSA) alone, SBE accounts for over 30,000 deaths per annum. Since 2017, SBE has been classified as a priority Neglected Tropical Disease (NTD) by the World Health Organisation (WHO). The major species responsible for mortality from SBE within SSA are from the Bitis, Dendroaspis, Echis and Naja genera. Pharmacologically active toxins such as metalloproteinases, serine proteinases, 3-finger toxins, kunitz-type toxins, and phospholipase A₂s are the primary snake venom components. These toxins induce cytotoxicity, coagulopathy, hemorrhage, and neurotoxicity in envenomed victims. Antivenom is currently the only available venom-specific treatment for SBE and contains purified equine or ovine polyclonal antibodies, collected from donor animals repeatedly immunized with low doses of adjuvanted venom. The resulting plasma or serum contains a high titre of specific antibodies, which can then be collected and stored until required. The purified antibodies are either whole IgG, monovalent fragment antibody (Fab) or divalent fragment antibody F(ab')₂. Despite pharmacokinetic and pharmacodynamic differences, all three are effective in the treatment of SBE. No antivenom is without adverse reactions but, the level of their impact and severity varies from benign early adverse reactions to the rarely occurring fatal anaphylactic shock. However, the major side effects are largely reversible with immediate administration of adrenaline and corticosteroids. There are 16 different antivenoms marketed within SSA, but the efficacy and safety profiles are only published for less than 50% of these products.

The WHO strategy for prevention and control of snakebite envenoming: a sub-Saharan Africa plan

Snakebite is a critical public health issue in tropical countries, particularly in Africa, where 20% of snakebites globally occur. In 2017, the WHO added snakebite envenoming to the category A of neglected tropical diseases. In 2019, thanks to broad institutional and international NGO support, including strong mobilization of African experts and governments, WHO launched a strategy for prevention and control of snakebite envenoming with more ambitious goals. In sub-Saharan Africa, accessibility of antivenoms and symptomatic, adjuvant or replacement therapy is a priority. Several antivenoms are available but their evaluation has not been properly carried out and they remain expensive. To date, there are no manufacturers of antivenom in sub-Saharan Africa (except in South Africa), which requires their importation from other continents. The lack of experience in antivenom choice and its use by health authorities, health personnel and population largely explains the shortage in sub-Saharan Africa. The deficiency of epidemiological data does not allow the implementation of appropriate and efficient care. It is crucial to strengthen the health system which does not have the necessary means for emergency management in general and envenoming in particular. Providing peripheral health centers with antivenoms would decrease complications and deaths. The motivation of communities at risk, identified through the epidemiological data, would be to reduce the delay in consultation that is detrimental to the efficiency of treatment. Partnerships need to be coordinated to optimize resources from international institutions, particularly African ones, and share the burden of treatment costs among all stakeholders. We propose here a project of progressive implementation of antivenom manufacturing in sub-Saharan Africa. The various steps, from the supply of appropriate venoms to the production of purified specific antibodies and vial filling, would be financed by international, regional and local funding promoting technology transfer from current manufacturers compensated by interest on the sale of antivenoms.

Reviewing evidence of the clinical effectiveness of commercially available antivenoms in sub-Saharan Africa identifies the need for a multi-centre, multi-antivenom clinical trial

Background

Snakebite envenoming kills more than more than 20,000 people in Sub-Saharan Africa every year. Poorly regulated markets have been inundated with low-price, low-quality antivenoms. This review aimed to systematically collect and analyse the clinical data on all antivenom products now available in markets of sub-Saharan Africa.

Methodology/Principal findings

Our market analysis identified 12 polyspecific and 4 monospecific antivenom products in African markets. Our search strategy was first based on a systematic search of publication databases, followed by manual searches and discussions with experts. All types of data, including programmatic data, were eligible. All types of publications were eligible, including grey literature. Cohorts of less than 10 patients were excluded. 26 publications met the inclusion criteria. Many publications had to be excluded because clinical outcomes were not clearly linked to a specific product. Our narrative summaries present product-specific clinical data in terms of safety and effectiveness against the different species and envenoming syndromes. Three products (EchiTabPlus, EchiTabG, SAIMR-Echis-monovalent) were found to have been tested in robust clinical studies and found effective against envenoming caused by the West African carpet viper (Echis ocellatus). Four products (Inoserp-Panafricain, Fav-Afrique, SAIMR-Polyvalent, Antivipmyn-Africa) were found to have been evaluated only in observational single-arm studies, with varying results. For nine other products, there are either no data in the public domain, or only negative data suggesting a lack of effectiveness.

Conclusions/Significance

Clinical data vary among the different antivenom products currently in African markets. Some products are available commercially although they have been found to lack effectiveness. The World Health Organization should strengthen its capacity to assess antivenom products, support antivenom manufacturers, and assist African countries and international aid organizations in selecting appropriate quality antivenoms.

Snakebite envenomation represents one of the most neglected tropical medical conditions worldwide. Despite high levels of morbidity and mortality associated with snakebite, its neglected nature has compromised the availability and evaluation of antivenom treatment. This review was initiated by Médecins Sans Frontières’ / Doctors Without Borders (MSF) Access Campaign, as the existing antivenom access crisis in sub-Saharan Africa was deepening. This study sought to review the clinical data pertaining to each antivenom product currently available for use in sub-Saharan Africa. 16 different antivenoms were identified. A total of 26 studies met the inclusion criteria. Given the heterogeneity of study methodology and quality, data for individual antivenoms are presented in the form of a narrative analysis. Only two studies reported clinical data collected from randomized controlled trials. Consistent monitoring of the side effects of antivenom treatment was lacking. The absence of good quality data for the majority of antivenoms in sub-Saharan Africa is a major concern. Further robust data collection is required, while urgent investments are needed at the global level to ensure a sustained production of safe and effective antivenom treatment, and its affordable access across sub-Saharan Africa.

Antivenom therapy: efficacy of premedication for the prevention of adverse reactions

Antivenoms or antitoxins have been effectively used for more than a century. During this time, these products have always proven to be highly effective in the treatment of infections and envenomations. However, antivenoms did not exhibit good safety results in their initial applications. After many improvements, antivenoms have substantially better safety profiles but still have some side effects. Due to the occurrence of adverse reactions, the practice of using premedication with the intent to decrease side effects has become accepted or mandatory in many countries. The drugs used for premedication belong to the histamine H1 antagonist, glucocorticoid and catecholamine groups. Currently, this practice is being questioned due to low or controversial efficacies in clinical assays. In this article, we discuss the causes of adverse reactions, the mechanisms of drugs that block the undesired effects and the results obtained in clinical trials. Although these three families of drugs could have positive effects on reducing adverse reactions, only adrenaline has demonstrated positive results in clinical assays.

Clinical and epidemiological aspects of scorpion stings in the northeast region of Brazil

Scorpion stings are a serious public health issue in tropical and subtropical countries. This is a descriptive and retrospective study of the clinical-epidemiological characteristics of scorpion sting cases registered in the Health System in the city of Campina Grande, Paraíba state, from 2007 to 2012. Data was collected from the Injury Notification Information System data banks of the Ministry of Health. A total of 2,283 records, provided by the Third Health Sector of Campina Grande, were analyzed. Data revealed that the majority of the victims are female aged between 20 and 29 years, and the highest incidence of stings was in the urban area. Victims were mostly stung on the feet and hand. Serotherapy was not administered in most cases. The majority of the victims received medical assistance within 1 to 3 hours after the sting. The most prevalent clinical manifestations were pain, edema and paresthesias. Most cases were classified as mild, though seven deaths were reported. The high incidence rate suggests that this town may be an endemic area of scorpion stings, supporting the need to develop strategies to control and prevent scorpion stings.

Scorpion-related cardiomyopathy: Clinical characteristics, pathophysiology, and treatment

CONTEXT

Scorpion envenomation is a threat to more than 2 billion people worldwide with an annual sting number exceeding one million. Acute heart failure presenting as cardiogenic shock or pulmonary edema, or both is the most severe presentation of scorpion envenomation accounting for 0.27% lethality rate.

OBJECTIVE

The purpose of this review is to characterize the scorpion-related cardiomyopathy, clarify its pathophysiological mechanisms, and describe potentially useful treatments in this particular context.

METHODS

We searched major databases on observational or interventional studies (whether clinical or experimental) on the cardiorespiratory consequences of scorpion envenomation and their treatment. No limit of age or language was imposed. A critical appraisal of the literature was conducted in order to provide a pathophysiological scheme that reconciles reported patterns of cardiovascular toxicity and hypotheses and assumptions made so far.

RESULTS

Early cardiovascular dysfunction is related to the so-called "vascular phase" of scorpion envenomation, which is related to a profound catecholamine-related vasoconstriction leading to a sharp increase in left ventricular (LV) afterload, thereby impeding LV emptying, and increasing LV filling pressure. Following this vascular phase, a myocardial phase occurs, characterized by a striking alteration in LV contractility (myocardial stunning), low cardiac output, and hypotensive state. The right ventricle involvement is symmetric to that of LV with a profound and reversible alteration in right ventricular performance. This phase is unique in that it is reversible spontaneously or under inotropic treatment. Scorpion myocardiopathy combines the features of takotsubo myocardiopathy (or stress myocardiopathy) which is linked to a massive release in catecholamines leading to myocardial ischemia through coronary vasomotor abnormalities (epicardial coronary spasm and/or increase in coronary microvascular resistance). Treatment of pulmonary edema due to scorpion envenomation follows the same principles as those applied for the treatment of cardiogenic pulmonary edema in general: this begins with oxygen supplementation targeting an oxygen saturation of 92% or more, by oxygen mask, continuous positive airway pressure, noninvasive ventilation, or conventional mechanical ventilation. Dobutamine effectively improves hemodynamic parameters and may reduce mortality in severe scorpion envenomation.

CONCLUSION

Scorpion cardiomyopathy is characterized by a marked and reversible alteration in biventricular performance. Supportive treatment relying on ventilatory support and dobutamine infusion is a bridge toward recovery in the majority of patients.

Post-exposure treatment of Ebola virus using passive immunotherapy: proposal for a new strategy

BACKGROUND

Better treatments are urgently needed for the management of Ebola virus epidemics in Equatorial Africa.

METHODS

We conducted a systematic review of the literature on the use of passive immunotherapy for the treatment or prevention of Ebola virus disease. We placed findings from this review into the context of passive immunotherapy currently used for venom-induced disease, and recent improvements in manufacturing of polyvalent antivenom products.

RESULTS

Passive immunotherapy appears to be one of the most promising specific treatments for Ebola. However, its potential has been incompletely evaluated, considering the overall experience and recent improvement of immunotherapy. Development and use of heterologous serum derivatives could protect people exposed to Ebola viruses with reasonable cost and logistics.

CONCLUSION

Hyperimmune equine IgG fragments and purified polyclonal whole IgG deserve further consideration as treatment for exposure to the Ebola virus.

Epidemiology of snakebite accidents in the municipalities of the state of Paraíba, Brazil

Accidents involving venomous animals represent an important, albeit neglected, public health issue worldwide. A descriptive study was made of snakebite cases attended and recorded between 2007 and 2010 in the health units of the municipalities of Cariri, State of Paraíba, northeastern Brazil. Data was collected from the Injury Notification Information System data banks of the Health Ministry and a total of 351 records of snakebite victims were reviewed. Victims were predominantly male farm workers over 50. The highest incidence of snakebites occurred in rural areas, between April and June of 2007 and 2010. Snakes of the genus Bothrops were responsible for most cases, and victims were mostly bitten on the feet. The majority of the victims received medical assistance within 1 to 3 hours after being bitten. The most common clinical manifestations were pain, edema and ecchymosis, which were mainly classified as mild or moderate. Two deaths were reported. It was concluded that there is a significant impact of seasonality in snakebites, the prevalence of attacks caused by Bothrops, affecting the lower limbs of adult male farmers in rural areas. The findings of this study may contribute to identify the conditions that increase the risk of snake attacks in the northeastern region.

Subacute coagulopathy in a randomized, comparative trial of Fab and F(ab')2 antivenoms

BACKGROUND

Envenomation by pit vipers is associated with coagulation disorders including hypofibrinogenemia and thrombocytopenia. These abnormalities correct following antivenom treatment during the acute phase of the disease. Delayed or recurrent coagulation abnormalities have been reported following use of Fab antivenom, resulting in risk of hemorrhage or death.

METHODS

We hypothesized that the longer plasma persistence of F(ab')2 antivenom, relative to Fab, in patients at risk of coagulopathy would result in decreased venonemia and coagulopathy one week after treatment. We conducted a Phase 2, randomized comparative clinical trial of rattlesnake bitten adults presenting for care in Tucson, Arizona, USA. Patients were randomly assigned to receive either Fab or F(ab')2 antivenom using a predefined treatment schedule. Endpoints included platelet counts, fibrinogen levels, and venom and antivenom ELISAs. Measurements were conducted at baseline and at various times over the following two weeks.

RESULTS

Twelve patients were studied, with 6 randomly assigned to each treatment group. Early response of platelet counts, fibrinogen, and venom levels to acute treatment was similar in the two groups. One week following treatment, platelet counts and fibrinogen levels were lower in the Fab group than in the F(ab')2 group, following a characteristic pattern that reached its lowest point approximately one week after initial treatment. Venom levels dropped below detection limits in all patients following initial treatment but subsequently rebounded into the measurable range in 4 of 6 Fab cases. F(ab')2 antivenom levels demonstrated a longer plasma persistence than Fab levels, with a less rapid drop during the two days following treatment. Two patients in the Fab group had significant adverse events involving coagulation abnormalities, for which additional antivenom was administered following the initial treatment period.

CONCLUSIONS

Following the acute phase of presentation and treatment for pit viper envenomation, there appears to be a roughly 2-week subacute phase of the disease during which ongoing presence of venom may result in serious delayed or recurrent coagulation defects. Late hypofibrinogenemia and thrombocytopenia are associated with recurrent venonemia and drop in antivenom levels. This pattern was apparent in patients treated with Fab antivenom but was not seen among F(ab')2 recipients in this Phase 2 study, consistent with pharmacokinetic differences between the two products. Improved understanding of Fab pharmacokinetics is important for the management of coagulopathy-prone pit viper envenomation. Use of F(ab')2 antivenom may prevent recurrent venom effects, but larger studies are necessary for statistical confirmation of this observation.

Emerging options for the management of scorpion stings

Scorpion stings are common in many tropical countries. Although most scorpion stings cause only localized pain without life-threatening envenoming, about one third of stings cause systemic envenoming which can result in death. Children are particularly sensitive to scorpion envenoming. The severity of scorpion stings is related to the presence of neurotoxins in the venom that cause a sudden release of neurotransmitters from the autonomic nervous system, predominantly sympathetic. There is also a strong inflammatory response that worsens symptoms, including those of a respiratory nature. Several vital functions may be directly affected, including the cardiovascular, respiratory, and neuromuscular systems. Hypertension is constant at the beginning of systemic envenoming and sometimes has a severe cardiac and respiratory impact. Although controversial, immunotherapy is the only etiological treatment. Administered early, it prevents many complications and improves the outcome. New antivenoms are highly purified immunoglobulin fragments, the efficacy and safety of which are excellent. As a consequence, adverse reactions to antivenoms are now very rare and usually mild, which should limit any reluctance regarding their routine use. Symptomatic treatment is still necessary to support immunotherapy, especially in cases of delayed arrival at hospital. A combination of both approaches should be considered, based on local resources and constraints.

Neutralization of Bothrops alternatus regional venom pools and individual venoms by antivenom: a systematic comparison

In this study we report that variation in lethality, hemorrhagic potency and procoagulation between individual samples of Bothrops alternatus venom from a single region, and variation between regional pools at the national level are comparable in range. Furthermore, the range of relative neutralization potencies of individual venoms within a region overlaps, and sometimes exceeds, the range of neutralization of regional venom pools throughout the country. Thus, the potency of neutralization of a national venom pool is poorly predictive of the potencies of neutralization of its constituent regional venom pools and, furthermore, the potency of neutralization of a regional venom pool is poorly predictive of the potencies of neutralization of its individual venom constituents. The efficiencies of neutralization of each of these effects (lethality, hemorrhage and procoagulation) were not significantly related to each other and did not correlate to the corresponding toxic potency of each venom or venom pool. Some implications of these findings are discussed in the context of the distinction between experimental quantitation of antivenom potency and the amount of antivenom that might be actually required to successfully treat two apparently comparable B. alternatus envenomations.

Clinical toxinology

Clinical toxinology is a specialized area of clinical medicine focused on the pathophysiology, diagnosis, treatment, and prevention of diseases caused by animal, plant, and fungal toxins. This review focuses on recent developments in snakebite. Snakebite is newly recognized as a Neglected Tropical Disease by the World Health Organization (WHO), reflecting the large human and economic cost of this disease. New WHO guidelines on antivenom production are available. The methods of producing antivenom and dosing are changing as understanding of envenoming improves. Lower antivenom doses in some regions are delivering equal outcomes, but antivenom cannot fully treat all envenoming types. Early antivenom treatment may reduce local tissue damage in some types of snakebite.

[Emergency immunotherapy: snake and scorpion antivenoms]

Passive immunotherapy was discovered in 1894. It is the only etiological treatment of envenomations by snakes or scorpions. Immunotherapy is based on administration of antibodies produced by an animal hyperimmunised against venom. Improvement of whole antivenomous sera was obtained, first by separating the antibodies from other components of blood plasma, then by using enzyme digestion of immunoglobulins G and, finally, by purifying the final product. Efficacy and also tolerance were significantly increased. Antivenom administration should be performed through the intravascular route to ensure better diffusion and to facilitate the complexion with the venom. The sale of antivenoms, in particular in Africa, is considerably reduced since about thirty years and is not in adequacy with the epidemiologic needs. In addition to the high cost of the current products, the difficulties of supplying, storage and use seem at the origin of this rejection by both the health staff and the victims who resort massively to traditional medicine. Whereas WHO reminds the rules of production and use of the antivenoms to producers and authorities in charge of drug regulations, it appears that the accessibility of the antivenoms depends on a concerted effort from all the actors, coordinated by health authorities: producers, distributers, manufacturers and public. Beyond technological improvements necessary in antivenom production, the strategy to be implemented must include the strict evaluation of the needs based on epidemiologic studies, the share of cost recovery between all the actors, and the optimization of the therapeutic protocol to make it applicable in remote health centres. Once confidence towards immunotherapy will be restored, mortality will be significantly reduced.

[Guidelines for the production, control and regulation of snake antivenom immunoglobulins]

Although frequent and severe, envenomations represent a neglected public health problem in most of the developing countries. Access to antivenoms is poor, mainly in Sub-Saharan Africa, and remains a major concern to World Health Organization (WHO). Since 2007, WHO committed international experts to propose guidelines aiming to improve the manufacture, quality control, registration and use of antivenoms. These guidelines, which will published soon, should promote access to antivenoms, and their use by health services, leading in the short term to a significant decrease of snakebite morbidity and mortality.