Oximes for acute organophosphate pesticide poisoning

2023 American Heart Association Focused Update on the Management of Patients With Cardiac Arrest or Life-Threatening Toxicity Due to Poisoning: An Update to the American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care

In this focused update, the American Heart Association provides updated guidance for resuscitation of patients with cardiac arrest, respiratory arrest, and refractory shock due to poisoning. Based on structured evidence reviews, guidelines are provided for the treatment of critical poisoning from benzodiazepines, β-adrenergic receptor antagonists (also known as β-blockers), L-type calcium channel antagonists (commonly called calcium channel blockers), cocaine, cyanide, digoxin and related cardiac glycosides, local anesthetics, methemoglobinemia, opioids, organophosphates and carbamates, sodium channel antagonists (also called sodium channel blockers), and sympathomimetics. Recommendations are also provided for the use of venoarterial extracorporeal membrane oxygenation. These guidelines discuss the role of atropine, benzodiazepines, calcium, digoxin-specific immune antibody fragments, electrical pacing, flumazenil, glucagon, hemodialysis, hydroxocobalamin, hyperbaric oxygen, insulin, intravenous lipid emulsion, lidocaine, methylene blue, naloxone, pralidoxime, sodium bicarbonate, sodium nitrite, sodium thiosulfate, vasodilators, and vasopressors for the management of specific critical poisonings.

Predictors of Mortality in Hospitalized Patients With Pesticide Poisoning

Background Organophosphorus poisoning (OPP) is a prevalent mortality rate that varies from 2% to 25% method of suicides worldwide. ICUs commonly employ various scoring systems such as the Glasgow Coma Scale (GCS), Acute Physiology and Chronic Health Evaluation II (APACHE II), Simplified Acute Physiology Score II (SAPS II), and International Programme on Chemical Safety (IPCS) Poison Severity Score (PSS) tools for risk stratification for mortality prediction scores and prognosis. This study aims to compare the predictive validity of these systems in hospitalized patients suffering from pesticide poisoning in a teaching hospital located in central India. Methods A prospective study design was utilized to gather relevant variables for calculating the GCS, APACHE II, SAPS II, and IPCS scales in patients affected by pesticide poisoning. Data on the administered doses of atropine and pralidoxime (PAM) were also recorded. Results We have identified several independent predictors of mortality among patients suffering from pesticide poisoning. The GCS (P=0.001), tracheostomy (P=0.001), APACHE II score (P=0.01), and SAPS II score (P=0.001) were all found to be significant indicators of mortality. Interestingly, the GCS demonstrated comparable predictive ability for mortality when compared to the APACHE II (0.82 (95% confidence interval (CI) 0.70 to 0.94)) and SAPS II (0.83 (95% CI 0.72 to 0.94)) scores, with no statistically significant difference (P=0.75) observed. Among the variables used in the IPCS PSS (GCS, heart rate, systolic blood pressure (BP), intubation, and pupil size), only GCS (P=0.05), and intubation (P=0.01) exhibited a significant association with mortality. Conclusions Our study determined that the GCS score, SAPS II, IPCS PSS, and APACHE II exhibited equal efficacy in predicting mortality. Notably, the GCS offered an added advantage due to its simplicity and minimal time requirements compared to the other scales.

Pretreatment of rhesus monkeys with transdermal patches containing physostigmine and procyclidine: implications of the delivery system for the potential application against VX nerve agent intoxication in humans

Physostigmine (Phs) is a reversible inhibitor of acetylcholinesterase (AChE) that penetrates the blood-brain barrier (BBB) and could be used to protect the central nervous system (CNS) against the effects of nerve agents. For prophylactic effectiveness, long, steady, and adequate inhibition of AChE activity by Phs is needed to broadly protect against the CNS effects of nerve agents. Here, we evaluated the efficacy of transdermal patches containing Phs and procyclidine (PC) as prophylactic agents. Patches (25 cm²) containing 4.4 mg Phs and 17.8 mg PC had a protective ratio of approximately 78.6-fold in rhesus monkeys challenged with VX nerve agent and given an antidote. Physiologically based pharmacokinetic model in conjunction with an indirect pharmacodynamic (PBPK/PD) was developed for Phs and scaled to rhesus monkeys. The model was able to reproduce the concentration profile and inhibitory effect on AChE of Phs in monkeys, as evidenced by correlation coefficients of 0.994 and 0.992 for 25 cm² and 49 cm² patches, respectively (i.e., kinetic data), and 0.989 and 0.968 for 25 cm² and 49 cm² patches, respectively (i.e., dynamic data). By extending the monkey PBPK/ PD model to humans, the effective human dose was predicted to be five applications of a 25 cm² patch (i.e., 22 mg Phs), and two applications of a 49 cm² patch (i.e., 17.4 mg Phs). Therefore, given that patch application of Phs in rhesus monkeys has a prolonged effect (namely, AChE inhibition of 19.6% for the 25 cm² patch and 23.0% for the 49 cm² patch) for up to 216 h, patch formulation of Phs may provide similar protection against nerve agent intoxication in humans.

Detection of Chlorpyrifos Using Bio-Inspired Silver Nanograss

Chlorpyrifos (CPF) is widely used as an organophosphorus insecticide; however, owing to developmental neurotoxicity, genotoxicity, and other adverse effects, it is harmful not only to livestock but also to humans. Therefore, the use of CPF was recently regulated, and its sensitive detection is crucial, as it causes serious toxicity, even in the case of residual pesticides. Because it is hard to detect the chlorpyrifos directly using spectroscopy (especially in SERS) without chemical reagents, we aimed to develop a SERS platform that could detect the chlorpyrifos directly in the water. In this study, we utilized the intrinsic properties of natural lawns that grow randomly and intertwine with each other to have a large surface area to promote photosynthesis. To detect CPF sensitively, we facilitated the rapid fabrication of biomimetic Ag nanograss (Ag-NG) as a surface-enhanced Raman spectroscopy (SERS) substrate using the electrochemical over-deposition method. The efficiency of the SERS method was confirmed through experiments and finite element method (FEM)-based electromagnetic simulations. In addition, the sensitive detection of CPF was enhanced by pretreatment optimization of the application of the SERS technique (limit of detection: 500 nM). The Ag-NG has potential as a SERS platform that could precisely detect organic compounds, as well as various toxic substances.

The Bradykinin B2 Receptor Agonist (NG291) Causes Rapid Onset of Transient Blood-Brain Barrier Disruption Without Evidence of Early Brain Injury

Background: The blood–brain barrier (BBB) describes the brain’s highly specialized capillaries, which form a dynamic interface that maintains central nervous system (CNS) homeostasis. The BBB supports the CNS, in part, by preventing the entry of potentially harmful circulating molecules into the brain. However, this specialized function is challenging for the development of CNS therapeutics. Several strategies to facilitate drug delivery into the brain parenchyma via disruption of the BBB have been proposed. Bradykinin has proven effective in disrupting mechanisms across the blood–tumor barrier. Unfortunately, bradykinin has limited therapeutic value because of its short half-life and the undesirable biological activity elicited by its active metabolites.

Objective: To evaluate NG291, a stable bradykinin analog, with selective agonist activity on the bradykinin-B2 receptor and its ability to disrupt the BBB transiently.

Methods: Sprague Dawley rats and CD-1 mice were subjected to NG291 treatment (either 50 or 100 μg/kg, intravenously). Time and dose-dependent BBB disruption were evaluated by histological analysis of Evans blue (EB) extravasation. Transcellular and paracellular BBB leakage were assessed by infiltration of ^99mTc-albumin (66.5 KDa) and ¹⁴C-sucrose (340 Da) radiolabeled probes into the brains of CD-1 mice treated with NG291. NG291 influence on P-glycoprotein (P-gp) efflux pump activity was evaluated by quantifying the brain accumulation of ³H-verapamil, a known P-gp substrate, in CD-1 mice.

Results: NG291-mediated BBB disruption was localized, dose-dependent, and reversible as measured by EB extravasation. ^99mTc-albumin leakage was significantly increased by 50 μg/kg of NG291, whereas 100 μg/kg of NG291 significantly augmented both ¹⁴C-sucrose and ^99mTc-albumin leakage. NG291 enhanced P-gp efflux transporter activity and was unable to increase brain uptake of the P-gp substrate pralidoxime. NG291 did not evoke significant short-term neurotoxicity, as it did not increase brain water content, the number of Fluoro-Jade C positive cells, or astrocyte activation.

Conclusion: Our findings strongly suggest that NG291 increases BBB permeability by two different mechanisms in a dose-dependent manner and increases P-gp efflux transport. This increased permeability may facilitate the penetration into the brain of therapeutic candidates that are not P-gp substrates.

Organophosphate poisoning from inappropriate topical use of malathion pesticide: A case report

A 43-year-old male with no past medical history presented to our emergency department with vomiting, diarrhea, and abdominal pain of 3 h’ duration. Upon further questioning, he revealed that he had been applying malathion pesticide over his body for the past 3 days for self-diagnosed scabies. He was otherwise afebrile and hemodynamically stable, and the physical examination was unremarkable. The patient was diagnosed with organophosphate poisoning and treated symptomatically due to the lack of worrying cardiorespiratory or neurologic sequelae. He was subsequently admitted to the general ward, where his symptoms abated within 4 h. Serum and red blood cell cholinesterase tests sent on admission returned on day three and were significantly decreased (serum cholinesterase 2131 U/L, reference range 4700–12000 U/L; red blood cell cholinesterase 3365 U/L, reference range 7700–14600 U/L). He was discharged home well and stable on day 5 of admission, with outpatient psychiatric follow-up for likely delusional parasitosis.

Lipid emulsion for the treatment of acute organophosphate poisoning: an Open-Label randomized trial

INTRODUCTION

Many organophosphate (OP) pesticides are lipid-soluble; therefore, intravenous lipid emulsion (ILE) has been evaluated as a possible treatment for acute poisoning. A single bolus dose of 100 ml of 20% ILE was found safe in a pilot observational study. This randomized trial aimed to assess the effectiveness and safety of an extended dose of ILE in acute OP poisoning.

METHODS

This was an investigator-initiated, parallel-group, open-label, randomized controlled trial conducted at PGIMER, Chandigarh (India), from January 2019 to June 2020, in patients aged above 13 years with acute OP poisoning. The primary efficacy outcome was to study the change in atropine dose requirement (total and over the first 24 h) for cholinergic crisis after giving an initial bolus dose of 100 ml of 20% ILE followed by an infusion of 100 ml of 20% ILE over 6 h in addition to the standard care. The secondary efficacy outcomes were to detect the effects on hemodynamic variables, length of hospital stay, and duration of mechanical ventilation required. The incidence of adverse events was evaluated.

RESULTS

A total of 45 patients were assigned to receive either ILE (intervention group, n = 23) or normal saline (control group, n = 22) in addition to standard treatment. Baseline variables in both groups were comparable. The median dose of atropine (in mg) in the first 24 h and at complete resolution in the ILE group were similar to the control group (124.0 versus 141.8, p-value 0.916; and 150.8 versus 175.0, p-value 0.935). Hemodynamic variables (systolic and diastolic blood pressures, mean arterial pressure, and pulse rate) over 24, 48, and 72 h of treatment, length of hospital stay, and duration of mechanical ventilation were also unaffected by ILE. Case fatality was 4 and not statistically different between intervention and control groups (1 versus 3, p-value 0.346). There was no excessive fever, dyspnea, elevation of serum amylase, or pancreatitis from ILE.

CONCLUSION

ILE has no apparent benefit in acute OP poisoning. However, an extended dose appears safe for the indication.

Computational Investigation of the Formation of Substituted Isoindole N-Oxides through the Photo-oxidative Cyclization of 2'-Alkynylacetophenone Oximes

Our recently published joint experiment-theory study of the photo-oxidative intramolecular cyclization of 2'-alkynylacetophenone oximes, performed in collaboration with the de Lijser group, presented the first reported formation of isoindole N-oxides. That study focused on determining a mechanistic explanation for the unexpected chemistry observed when three 2'-alkynylacetophenone oximes were photo-oxidized with 9,10-dicyanoanthracene (DCA), specifically the derivatives with a phenyl, isopropyl, or n-butyl substituent at the alkynyl group. Here, we use density functional theory to develop a broader understanding of the scope of this chemistry. In particular, we demonstrate that substituents on the alkynyl group and on the central benzene ring can significantly modulate the thermodynamic driving force for oxime radical cation generation when DCA is used as the photosensitizer. In contrast, substituents are shown to have a small impact on the chemical reactivity of the radical cation intermediates. In particular, 5-exo radical cation cyclization, which ultimately results in an isoindole N-oxide product, is always kinetically and sometimes also thermodynamically preferred over 6-endo radical cation cyclization, which would produce an isoquinoline N-oxide product. Overall, this study provides mechanistic insights into the diversity of isoindole N-oxides that can be produced through the photo-oxidative cyclization of 2'-alkynylacetophenone oximes.

Cardiac injury in organophosphate poisoning after acute ingestion

Introduction

Sparse data and conflicting evidence exist on the prevalence and prognosis of organophosphate (OP)-related cardiac toxicity. We aimed to characterize the cardiac abnormalities of OP after an acute cholinergic crisis in adults without previous cardiovascular conditions.

Patients and Methods

We did a prospective observational study in a tertiary-care hospital of north India (Postgraduate Institute of Medical Education and Research, Chandigarh) in 74 patients aged ≥ 13 years admitted with acute OP poisoning after self-ingestion. A systemic evaluation, including clinical characteristics, electrocardiography, and echocardiography, was performed to estimate the prevalence and prognosis of cardiac injury. A rate-corrected QT interval was calculated using Bazett's method, and >440 milliseconds was used to define prolongation.

Results

Chlorpyrifos was the most commonly ingested OP (n = 29). The patients had a similar occurrence of hypotension (n = 10) and hypertension (n = 9) at admission, and electrocardiography demonstrated sinus tachycardia in 38 (51.3%) and sinus bradycardia in one case. During the hospital stay, 3 out of 74 patients had a prolonged rate-corrected QT interval (457, 468, and 461 milliseconds), and one patient developed supraventricular tachycardia. Eight (10.8%) patients developed the intermediate syndrome, and six (8.1%) died. None of the hemodynamic or electrocardiographic abnormalities was associated with in-hospital mortality or intermediate syndrome development on univariant analysis. Baseline echocardiography at hospital discharge was performed in 27 patients (admitted during 2018) and normal in all except mild tricuspid regurgitation in one. At a 6-month follow-up, 23 cases were available for cardiovascular screening (including echocardiography) and had a normal evaluation.

Conclusion

Cardiac toxicity is uncommon after acute OP self-ingestion and lacks prognostic significance.

Mechanistic Investigation of the Formation of Isoindole N-Oxides in the Electron Transfer-Mediated Oxidative Cyclization of 2'-Alkynylacetophenone Oximes

This paper describes a joint experiment-theory investigation of the formation and cyclization of 2'-alkynylacetophenone oxime radical cations using photoinduced electron transfer (PET) with DCA as the photosensitizer. Using a combination of experimental ¹H and ¹³C nuclear magnetic resonance (NMR) spectra, high-resolution mass spectrometry, and calculated NMR chemical shifts, we identified the products to be isoindole N-oxides. The reaction was found to be stereoselective; only one of the two possible stereoisomers is formed under these conditions. A detailed computational investigation of the cyclization reaction mechanism suggests facile C-N bond formation in the radical cation leading to a 5-exo intermediate. Back-electron transfer from the DCA radical anion followed by barrierless intramolecular proton transfer leads to the final product. We argue that the final proton transfer step in the mechanism is responsible for the stereoselectivity observed in experiment. As a whole, this work provides new insights into the formation of complex heterocycles through oxime and oxime ether radical cation intermediates produced via PET. Moreover, it represents the first reported formation of isoindole N-oxides.

Acetylcholinesterase inhibition resulting from exposure to inhaled OP can be prevented by pretreatment with BChE in both macaques and minipigs

More frequent and widespread nerve agent attacks highlight the need for efficacious pre- and post-exposure organophosphate (OP) counter-measures to protect military and civilian populations. Because of critical targeting of acetylcholinesterase (AChE) in the CNS by OPs, a pre-treatment candidate for preventing/reducing poisoning will be a broadly acting molecule that scavenges OPs in blood before they reach their physiological targets. Prophylactic human butyrylcholinesterase (HuBChE), the leading pretreatment candidate, has been shown to protect against multiple LD50's of nerve agents in rodents, macaques, and minipigs. This review describes the development of a HuBChE bioscavenger pretreatment from early proof-of-concept studies to pre-clinical studies with the native injectable enzyme and the development of aerosolized forms of recombinant enzyme, which can be delivered by inhalation nebulizer devices, to effect protection against inhaled OP nerve agents and insecticides. Early animal studies utilized parenteral exposure. However, lungs are the portal of entry for most volatile OP vapors and represent the major means of OP intoxication. In this regard, pretreat-ment with 7.5 mg/kg of HuBChE by IM injection protected minipigs against lethal sarin vapor and prevented AChE inhibition in the blood. This is similar to the five-day protection in macaques by an aerosolized rHuBChE using a nebulizer against aerosolized paraoxon (estimated to be an 8 mg/kg estimated human dose). Importantly, lethal inhaled doses of OP may be smaller relative to the same dose delivered by injection, thus reducing the protective HuBChE dose, while a combination of HuBChE and post-exposure oxime may prolong protection.

Safety and Efficacy of New Oximes to Reverse Low Dose Diethyl-Paraoxon-Induced Ventilatory Effects in Rats

Background: Oximes are used in addition to atropine to treat organophosphate poisoning. However, the efficiency of oximes is still a matter of debate. In vitro experiments suggested than new oximes are more potent than the commercial oximes. However, the antidotal activity of new oximes has not been assessed in vivo. Methods: The aim of this work was to assess the safety and efficiency of new oximes compared to pralidoxime in a rat model of diethyl paraoxon-induced non-lethal respiratory toxicity. Results: Safety study of oximes showed no adverse effects on ventilation in rats. KO-33, KO-48, KO-74 oximes did not exhibit significant antidotal effect in vivo. In contrast, KO-27 and BI-6 showed evidence of antidotal activity by normalization of respiratory frequency and respiratory times. KO-27 became inefficient only during the last 30 min of the study. In contrast, pralidoxime demonstrated to be inefficient at 30 min post injection. Inversely, the antidotal activity of BI-6 occurred lately, within the last 90 min post injection. Conclusion: This study showed respiratory safety of new oximes. Regarding, the efficiency, KO-27 revealed to be a rapid acting antidote toward diethylparaoxon-induced respiratory toxicity, meanwhile BI-6 was a late-acting antidote. Simultaneous administration of these two oximes might result in a complete and prolonged antidotal efficiency.

The Efficacy of Pralidoxime in the Treatment of Organophosphate Poisoning in Humans: A Systematic Review and Meta-analysis of Randomized Trials

Introduction

The benefits of atropine in the treatment of acute organophosphate (OP) poisoning has been well established, while that of oximes is still uncertain. Pralidoxime is the most often used oxime worldwide. In vitro experiments have consistently shown that oximes are effective reactivators of human acetylcholinesterase enzyme, inhibited by OP compounds. However, the clinical benefit of pralidoxime is still unclear. A recent meta-analysis has found that pralidoxime provides no significant improvement in outcome and rather may cause harm while increasing the economic burden in low-income communities where its use is the most prevalent.

Objectives

This study aimed to provide an updated evaluation of the efficacy of pralidoxime in addition to atropine alone in the treatment of patients with acute OP poisoning in terms of mortality, need for ventilator support, and the incidence of intermediate syndrome. The intermediate syndrome is a clinical syndrome that occurs 24 to 96 hours after the ingestion of an OP compound and is characterized by prominent weakness of neck flexors, muscles of respiration, and proximal limb muscles. 

Materials and methods

We searched MEDLINE, EMBASE, CENTRAL, and ClinicalTrials.gov databases until January 2019 for randomized controlled trials (RCTs) in the English language that evaluated the use of pralidoxime in individuals of any age, gender or nationality presenting with an alleged history of OP intake. The primary outcome was mortality. Secondary outcomes were the need for ventilator support and the incidence of intermediate syndrome. The risk of bias in included studies was assessed using the tool recommended by the Cochrane Handbook of Systematic Review of Interventions. Treatment/control differences in these outcomes across included studies were combined using risk ratios (RR).

Results

Six randomized controlled trials (n = 646) fulfilled the inclusion criteria, including one further trial missed from the most recent systematic review. The risk of bias varied across studies, with Eddleston 2009 being of the lowest risk and Cherian 2005 being of high risk. The risk of mortality (RR = 1.53, 95% confidence interval (CI) 0.97 to 2.41, P = 0.07) and the need for ventilator support (RR = 1.29, 95% CI 0.97 to 1.71, P = 0.08) were not significantly different between the pralidoxime and the control group. There was a significant increase in the incidence of intermediate syndrome in the pralidoxime group (RR = 1.63; 95% CI 1.01 to 2.62, P = 0.04).

Conclusions

Based on our meta-analysis of the available RCTs, pralidoxime was not shown to be beneficial in patients with acute OP poisoning. Our findings are consistent with the other literature.

Clinical effects from household insecticide: pyrethroid or organophosphate toxicity?

A 54-year-old man with a history of schizophrenia presented to the emergency room for weakness with associated lacrimosis, drooling, nausea, emesis, diarrhoea, diplopia and burning sensation on his skin that began 6 hours after spraying five cans of Raid on his carpet. He was noted to have miotic pupils and hyperactive bowel sounds. Given the clinical presentation, the patient was diagnosed with organophosphate (OP) toxicity. After being admitted, he developed symptoms associated with his OP toxicity and was successfully treated with atropine and pralidoxime. Most Raid products contain pyrethroids; however, both OPs and pyrethroids are available in commercial pesticides and patients may misidentify ingestions. There are limited data reporting the toxicity of pyrethroid overdose in humans and to guide its subsequent treatment. It is crucial to keep a low threshold for diagnosing and treating patients with acute onset of symptoms suspicious for an OP or pyrethroid toxidrome.

Efficacy of an organophosphorus hydrolase enzyme (OpdA) in human serum and minipig models of organophosphorus insecticide poisoning

Objectives: Current therapeutic options for organophosphorus (OP) insecticide self-poisoning including atropine and oximes are inadequate and case fatality may exceed 20%. An OP hydrolase enzyme, OpdA, has been used for environmental cleansing of OP insecticides and prevented death in rat and non-human primate models of OP insecticide poisoning if given very quickly after exposure. We here tested OpdA's ability to break down OP insecticides in human serum and in clinically relevant minipig models of OP insecticide poisoning.Methods: Human serum was spiked with seven diverse WHO Class II OP insecticides (chlorpyrifos, quinalphos, diazinon, dimethoate, fenthion, phenthoate, and profenofos) and the effect of OpdA on degradation measured. The pharmacodynamic and clinical effects of OpdA treatment were studied in Gottingen minipigs orally poisoned with agricultural formulations of dimethoate EC40 or methyl parathion EC60; pharmacodynamic effects were also assessed in profenofos EC50-poisoned pigs.Results: OpdA effectively hydrolysed OP insecticides in human serum, with rates varying from 856 (SD 44) down to 0.107 (SD 0.01) moles of substrate hydrolysed/mole of enzyme/sec (k_cat) for quinalphos and phenthoate, respectively, although at rates 2-3 log orders less than found in vitro in buffered solution. It showed clinical benefit in minipig models, reducing the dose of noradrenaline required to sustain an adequate mean arterial pressure after dimethoate (mean 0.149 [SD 0.10] μg/kg/h vs. 1.07 [SD 0.77] μg/kg/h, p < .0001) and methyl parathion (mean 0.077 [SD 0.08] μg/kg/h vs. 0.707 [SD 0.49] μg/kg/h, p < .0001) poisoning. OpdA reduced blood OP insecticide concentration and acetylcholinesterase inhibition after poisoning by dimethoate, methyl parathion, and profenofos insecticides.Conclusions: In vitro incubation of OpdA in human serum showed hydrolysis of diverse OP insecticides, although at lower rates than found in buffer solutions. This activity results in clinical and pharmacodynamic efficacy in vivo against several OP insecticides. These results support the testing of OpdA in further animal models before considering human trials to determine whether it may become an urgently required novel therapeutic agent for OP insecticide self-poisoning.

Aerosolized recombinant human butyrylcholinesterase delivered by a nebulizer provides long term protection against inhaled paraoxon in macaques

The recent intentional use of nerve agents and pesticides in Europe and Afghanistan highlights the need for an effective countermeasure against organophosphates (OP) toxins. The most developed pretreatment candidate to date is plasma (native) human butyrylcholinesterase (HuBChE), which is limited in availability and because of its 1:1 stoichiometry with OPs, a large dose will present challenges when delivered parenterally both in terms of pharmacokinetics and manageability in the field. A tetrameric recombinant (r) form of human BChE produced in CHO-K1 cells with similar structure, in vivo stability and antidotal efficacy as the native form, has been developed to deliver rHuBChE as an aerosol (aer) to form a pulmonary bioshield capable of neutralizing inhaled OPs in situ and prevent AChE inhibition in the blood and in the brain; the latter associated with the symptoms of OP toxicity. Previous proof-of-concept macaque studies demonstrated that delivery of 9 mg/kg using a microsprayer inserted down the trachea, resulted in protection against an inhaled dose of 15ug/kg of aer-paraoxon (aer-Px) given 72 h later. In the present studies, pulmonary delivery of rHuBChE in macaques was achieved using Aerogen vibrating mesh nebulizers, similar to that used for human self-administration. The promising findings indicate that despite the poor lung deposition observed in macaques using nebulizers (13-20%), protective levels of RBC-AChE were still present in the blood even when exposure aer-Px (55 μg/kg) was delayed for five days. This long term retention of 5 mg/kg rHuBChE deposited in the lung bodes well for the use of an aer-rHuBChE pretreatment in humans where a user-friendly customized nebulizer with increased lung deposition up to 50% will provide even longer protection at a lower dose.

The Experimental Oxime K027-A Promising Protector From Organophosphate Pesticide Poisoning. A Review Comparing K027, K048, Pralidoxime, and Obidoxime

Poisoning with organophosphorus compounds (OPCs) is a major problem worldwide. Standard therapy with atropine and established oxime-type enzyme reactivators (pralidoxime, obidoxime) is unsatisfactory. In search of more efficacious broad-spectrum oximes, new bispyridinium (K-) oximes have been synthesized, with K027 being among the most promising. This review summarizes pharmacokinetic characteristics of K027, its toxicity and in vivo efficacy to protect from OPC toxicity and compares this oxime with another experimental bisquaternary asymmetric pyridinium aldoxime (K048) and two established oximes (pralidoxime, obidoxime). After intramuscular (i.m.) injection, K027 reaches maximum plasma concentration within ∼30 min; only ∼2% enter the brain. Its intrinsic cholinesterase inhibitory activity is low, making it relatively non-toxic. In vitro reactivation potency is high for ethyl-paraoxon-, methyl-paraoxon-, dichlorvos-, diisopropylfluorophosphate (DFP)- and tabun-inhibited cholinesterase. When administered in vivo after exposure to the same OPCs, K027 is comparable or more efficacious than pralidoxime and obidoxime. When given as a pretreatment before exposure to ethyl-paraoxon, methyl-paraoxon, DFP, or azinphos-methyl, it is superior to the Food and Drug Administration-approved compound pyridostigmine and comparable to physostigmine, which because of its entry into the brain may cause unwanted behavioral effects. Because of its low toxicity, K027 can be given in high dosages, making it a very efficacious oxime not only for postexposure treatment but also for prophylactic administration, especially when brain penetration is undesirable.

Uso de pralidoxima en la intoxicación con metomilo en pastor collie en Medellín (Colombia). Reporte de caso

Se describe el uso de la pralidoxima en el tratamiento de una intoxicación con metomiloen un canino en la ciudad de Medellín (Colombia). Un macho de raza pastor colliesufrió intoxicación accidental con metomilo, presentó cuadro colinérgico, con miosis,sialorrea, delirio, excitación y emesis, fue sometido a descontaminación con carbónactivado y terapia con atropina (0,04 mg/kg IM) cada 30 minutos hasta atropinizar,difenhidramina (2 mg/kg EV) y pralidoxima (10 mg/kg EV) cada 8 horas y pentobarbital(12 mg/kg EV) por 24 horas, además de terapia de sostén. Se realizaron pruebashematológicas, creatinina, alanino aminotrasferasa, tiempo de protrombina y tiempoparcial tromboplastina que resultaron normales para la especie. Después de una terapiade 7 días el paciente presentó mejoría total de los signos nerviosos y se dio de alta encondición normal. El uso de pralidoxima como activador de la acetilcolinesterasa es unaopción en el tratamiento de la intoxicación grave por metomilo en la especie canina quemuestra sensibilidad a los carbamatos.

Prediction of organophosphorus insecticide-induced intermediate syndrome with stimulated concentric needle single fibre electromyography

BACKGROUND

Deliberate self-poisoning (DSP) using organophosphorus (OP) insecticides are a common clinical problem in Asia. OPs inhibit acetylcholine esterase (AChE), leading to over-activity of muscarinic and nicotinic cholinergic circuits. Intermediate syndrome (IMS) is mediated via prolonged nicotinic receptor stimulation at the neuromuscular junction and its onset is between 24-96 hours post ingestion. The aims of the present study were 1) to investigate whether neuromuscular junction dysfunction within the first 24 hours following exposure, quantified by jitter in single fibre electromyography (SfEMG), can predict IMS, and 2) to compare the changes in SfEMG jitter over the course of the illness among patients who developed IMS (IMS+) and those who did not (IMS-).

METHODS AND FINDINGS

We conducted a prospective cohort study in a tertiary care hospital in Sri Lanka on 120 patients admitted between September 2014 and August 2016 following DSP by OP insecticides viz., profenofos 53, phenthoate 17, diazinon 13, chlorpyrifos 5, others 12, unknown 20. SfEMG was performed every second day during hospitalization. Exposure was confirmed based on the history and red blood cell AChE assays. IMS was diagnosed in patients who demonstrated at least three out of four of the standard IMS criteria: proximal muscle weakness, bulbar muscle weakness, neck muscle weakness, respiratory paralysis between 24-96 hours post ingestion. Respiratory failure requiring intubation occurred in 73 out of 120 patients; 64 of these were clinically diagnosed with IMS. Of the 120 patients, 96 had repeated SfEMG testing, 67 of them being tested within the first 24 hours. Prolonged jitter (>33.4μs) within the first 24 hours was associated with greatly increased risk of IMS (odds ratio = 8.9, 95% confidence intervals = 2.4-29.6, p = 0.0003; sensitivity 86%, specificity 58%). The differences in jitter between IMS+ and IMS- patients remained significant for 72 hours and increased jitter was observed in some patients for up to 216 hours. For intubated patients, the median time for jitter to normalize and median time to extubate were similar, and the two variables had a moderate positive correlation (r = 0.49, P = 0.001).

CONCLUSIONS

Prolonged jitter recorded with SfEMG <24 hours of ingestion of an OP strongly correlates with subsequent occurrence of IMS. The time course of electrophysiological recovery of the NMJ was similar to the time course of respiratory recovery in IMS patients.

Utility of 2-Pyridine Aldoxime Methyl Chloride (2-PAM) for Acute Organophosphate Poisoning: A Systematic Review and Meta-Analysis

Organophosphates (OP) account for the majority of pesticide-related unintentional or intentional poisonings in lower- and middle-income countries. The therapeutic role of atropine is well-established for patients with acute OP poisoning. The benefit of adding 2-pyridine aldoxime methyl chloride (2-PAM), however, is controversial. We performed a systematic review and meta-analysis of available randomized controlled trials (RCT) to compare 2-PAM plus atropine in comparison to atropine alone for acute OP poisoning. We searched PubMed, EMBASE, and SCOPUS up to March 2017. The Cochrane review handbook was used to assess the risk of bias. Data were abstracted and risk ratios (RR) were calculated for mortality, rate of intubation, duration of intubation, intermediate syndrome, and complications such as hospital-acquired infections, dysrhythmias, and pulmonary edema. We found five studies comprising 586 patients with varying risks of bias. The risk of death (RR = 1.5, 95% CI 0.9-2.5); intubation (RR = 1.3, 95% CI 1.0-1.6); intermediate syndrome (RR = 1.6, 95% CI 1.0-2.6); complications (RR = 1.2, 95% CI 0.8-1.8); and the duration of intubation (mean difference 0.0, 95% CI - 1.6-1.6) were not significantly different between the atropine plus 2-PAM and atropine alone. Based on our meta-analysis of the available RCTs, 2-PAM was not shown to improve outcomes in patients with acute OP poisoning.

Post-exposure treatment with the oxime RS194B rapidly reactivates and reverses advanced symptoms of lethal inhaled paraoxon in macaques

Fatalities from organophosphate (OP) insecticide result from both occupational and deliberate exposure; significantly impacting human health. Like nerve agents, insecticides are neurotoxins which target and inhibit acetylcholinesterases (AChE) in central and peripheral synapses in the cholinergic nervous system. Post-exposure therapeutic countermeasures generally include administration of atropine with a pyridinium aldoxime e.g. pralidoxime, to reactivate the OP-inhibited AChE. However, commonly used oximes inefficiently cross the bloodbrain barrier and are rapidly cleared and their benefit is debated. Recent findings have demonstrated the ability of a novel zwitterionic, centrally acting, brain penetrating oxime (RS194B) to reverse severe symptoms and rapidly reactivate sarin-inhibited AChE in macaques, but it has not been tested following OP pesticide poisoning. In the present study, the symptoms following a lethal dose of inhaled paraoxon (100ug/kg), were shown to mimic those in insecticide poisoned individuals and were also rapidly reversed in macaques by post-exposure IM administration of 80mg/kg of RS194B. This occurred with a concomitant reactivation of AChE to 40-100% in<1hr and BChE (40% in 8h). These findings will be used to develop a macaque model with RS194B as a post-exposure treatment for insecticide poisoning and generate efficacy data for approval under the FDA Animal rule.

Post-exposure treatment with the oxime RS194B rapidly reverses early and advanced symptoms in macaques exposed to sarin vapor

Organophosphate (OP) nerve agents and pesticides trigger a common mechanism of neurotoxicity resulting from critical targeting and inhibition of acetylcholinesterases (AChE) in central and peripheral synapses in the cholinergic nervous system. Therapeutic countermeasures have thus focused on either administering an oxime post-exposure, that can rapidly reactivate OP-inhibited AChE, or by preventing OP poisoning through administering pre-exposure treatments that scavenge OPs before they inhibit their physiological AChE targets. While several pyridinium aldoxime antidotes are currently approved, their utility is impaired due to their inability to cross the blood-brain barrier (BBB) efficiently. The present study utilized a macaque (Ma) model to demonstrate the efficacy of a novel zwitterionic and centrally acting oxime RS194B to reactivate sarin- and paraoxon-inhibited macaque AChE and butyrylcholinesterase (BChE) in vitro and to further assess the capacity of RS194B to effect a reversal of clinical symptoms following sarin inhalation in vivo. In vitro, oxime reactivation of MaAChE and MaBChE was shown to be comparable to their human orthologs, while the macaque studies indicated that IM administration of 62.5 mg/kg of RS194B and 0.28 mg/kg atropine after continuous exposure to 49.6 μg/kg sarin vapor, rapidly reactivated the inhibited AChE and BChE in blood and reversed both early and advanced clinical symptoms of sarin-induced toxicity following pulmonary exposure within 1 h. The rapid cessation of autonomic and central symptoms, including convulsions, observed in macaques bodes well for the use of RS194B as an intra- or post-exposure human treatment and validates the macaque model in generating efficacy and toxicology data required for approval under the FDA Animal rule.

Acute Renal Failure due to Organophosphate Poisoning: A Case Report

Organophosphate (OP) poisoning is a commonly seen condition in many countries. OP poisoning classically presents with symptoms of cholinergic excess. It can rarely affect other organ systems but when it does, it can worsen a patient's overall prognosis. We present a case of a 23-year-old man with an extremely rare case of acute kidney injury due to OP, who was successfully treated with a combination of hemodialysis, atropine and pralidoxime days after OP poisoning with reservations on the aging process.

Efficacy of fresh packed red blood transfusion in organophosphate poisoning

The mortality rate caused by organophosphate (OP) poisoning is still high, even the standard treatment such as atropine and oxime improves a lot. To search for alternative therapies, this study was aimed to investigate the effects of packed red blood cell (RBC) transfusion in acute OP poisoning, and compare the therapeutic effects of RBCs at different storage times.Patients diagnosed with OP poisoning were included in this prospective study. Fresh RBCs (packed RBCs stored less than 10 days) and longer-storage RBCs (stored more than 10 days but less than 35 days) were randomly transfused or not into OP poisoning patients. Cholinesterase (ChE) levels in blood, atropine usage and durations, pralidoxime durations were measured.We found that both fresh and longer-storage RBCs (200-400 mL) significantly increased blood ChE levels 6 hours after transfusion, shortened the duration for ChE recovery and length of hospital stay, and reduced the usage of atropine and pralidoxime. In addition, fresh RBCs demonstrated stronger therapeutic effects than longer-storage RBCs.Packed RBCs might be an alternative approach in patients with OP poisoning, especially during early stages.

Study of Effect of Magnesium Sulphate in Management of Acute Organophosphorous Pesticide Poisoning

Background:

Organophosphorus compound poisoning (OPCP) is a major public health problem in developing countries like India. Atropine and oximes remain the main-stay of management. Magnesium sulfate (MgSO₄) has shown benefit in the management of OPCP.

Aims:

This study was designed to assess the effect of MgSO₄ on outcome in OPCP patients admitted to Intensive Care Unit (ICU).

Settings and Design:

Double-blind prospective randomized clinical trial in an ICU of tertiary care institution.

Methods:

One hundred patients (50 in each group) of OPCP, confirmed by history and syndrome of OPCP with low plasma pseudocholinesterase, aged between 18 and 60 years were studied. Magnesium group (Group M) received 4 g of 20% MgSO₄ infusion over 30 min at admission to ICU, control group (Group C) received normal saline placebo in the same manner. Patients were assessed for the need for intubation, requirement of atropine, duration of mechanical ventilation, duration of ICU stay, and its effect on mortality.

Statistical Analysis:

Chi-square test and Fisher's exact test for categorical data, independent sample t-test, and paired t-test for nominal data.

Results:

Demographics and basal serum magnesium levels were comparable. Atropine requirement was higher in Group C (74.82 ± 22.39 mg) compared to Group M (53.11 ± 45.83 mg) (P < 0.001). A total of 33 patients in Group C and 23 patients in Group M required intubation, respectively (P = 0.043). The mean duration of mechanical ventilation was 4.51 ± 2 days in Group C compared to 4.13 ± 1.6 days in Group M (P = 0.45). ICU stay was 5.36 ± 2.018 days in Group C compared to 4.54 ± 1.581 days in Group M (P = 0.026). There was no significant difference in mortality between the groups.

Conclusion:

Four grams of MgSO₄ given to OPCP patients within 24 h of admission to ICU, decreases atropine requirement, need for intubation, and ICU stay.

The effectiveness of patient-tailored treatment for acute organophosphate poisoning

BACKGROUND

To determine a new pralidoxime (PAM) treatment guideline based on the severity of acute organophosphate intoxication patients, APACHE II score, and dynamic changes in serum butyrylcholinesterase (BuChE) activity.

METHODS

This is a randomization trial. All patients received supportive care measurements and atropinization. Each enrolled patient was treated with 2 gm PAM intravenously as the loading dose. The control group was treated according to the WHO's recommended PAM regimen, and the experimental group was treated according to their APACHE II scores and dynamic changes in BuChE activity. If a patient's APACHE II score was ≧26 or there was no elevation in BuChE activity at the 12th hour when compared to the 6th, doses of 1 g/h PAM (i.e., doubled WHO's recommended PAM regimen) were given. The levels of the serum BuChE and red blood cells acetylcholinesterase and the serum PAM levels were also measured.

RESULTS

Forty-six organophosphate poisoning patients were enrolled in this study. There were 24 patients in the control group and 22 patients in the experimental group. The hazard ratio of death in the control group to that of the experimental group was 111.51 (95% CI: 1.17-1.613.45; p = 0.04). The RBC acetylcholinesterase level was elevated in the experimental group but was not in the control group. The experimental group did not exhibit a higher PAM blood level than did the control group.

CONCLUSION

The use of PAM can be guided by patient severity. Thus, may help to improve the outcomes of organophosphate poisoning patients.

The Effect of Parathion on Red Blood Cell Acetylcholinesterase in the Wistar Rat

Organophosphorus (OP) pesticide poisoning is a significant problem worldwide. Research into new antidotes for these acetylcholinesterase inhibitors, and even optimal doses for current therapies, is hindered by a lack of standardized animal models. In this study, we sought to characterize the effects of the OP pesticide parathion on acetylcholinesterase in a Wistar rat model that included comprehensive medical care. Methods. Male Wistar rats were intubated and mechanically ventilated and then poisoned with between 20 mg/kg and 60 mg/kg of intravenous parathion. Upon developing signs of poisoning, the rats were treated with standard critical care, including atropine, pralidoxime chloride, and midazolam, for up to 48 hours. Acetylcholinesterase activity was determined serially for up to 8 days after poisoning. Results. At all doses of parathion, maximal depression of acetylcholinesterase occurred at 3 hours after poisoning. Acetylcholinesterase recovered to nearly 50% of baseline activity by day 4 in the 20 mg/kg cohort and by day 5 in the 40 and 60 mg/kg cohorts. At day 8, most rats' acetylcholinesterase had recovered to roughly 70% of baseline. These data should be useful in developing rodent models of acute OP pesticide poisoning.

Mitigation of diazinon-induced cardiovascular and renal dysfunction by gallic acid

Studies of the link between environmental pollutants and cardiovascular dysfunction, neglected for decades, have recently provided new insights into the pathology and consequences of these killers. In this study, rats were divided into four groups, each containing 10 rats. The rats in group one served as controls and were administered normal saline, whereas the rats in group two were orally gavaged with 3 mg/kg of diazinon (DZN) alone for twenty one consecutive days. The rats in groups 3 and 4 were administered respective 60 mg/kg and 120 mg/kg gallic acid (GA) in addition to DZN for twenty one consecutive days. Exposure of rats to diazinon significantly (p<0.05) reduced the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and reduced glutathione (GSH) content. Malondialdehyde, hydrogen peroxide (H2O2) and nitric oxide (NO) contents were also significantly (p<0.05) elevated following DZN exposure. DZN further caused a significant (p<0.05) decrease of heart rate and QT interval prolongation. Hematologic analysis revealed significant reduction (p<0.05) in packed cell volume (PCV), hemoglobin concentration (Hb), red blood cell (RBC) count, and total white blood cell count of rats administered only DZN. Observations in this study suggest a modulatory role of gallic acid in diazinon-induced anemia and associated cardiovascular dysfunction in rats. Treatment with gallic acid reversed the oxidative stress markers studied, increased the antioxidant defence system and reduced deleterious effects on hematological parameters in rats. Pathologic findings of the heart and kidney were also found to be lessened.

Intranasal delivery of obidoxime to the brain prevents mortality and CNS damage from organophosphate poisoning

Intranasal delivery is an emerging method for bypassing the blood brain barrier (BBB) and targeting therapeutics to the CNS. Oximes are used to counteract the effects of organophosphate poisoning, but they do not readily cross the BBB. Therefore, they cannot effectively counteract the central neuropathologies caused by cholinergic over-activation when administered peripherally. For these reasons we examined intranasal administration of oximes in an animal model of severe organophosphate poisoning to determine their effectiveness in reducing mortality and seizure-induced neuronal degeneration. Using the paraoxon model of organophosphate poisoning, we administered the standard treatment (intramuscular pralidoxime plus atropine sulphate) to all animals and then compared the effectiveness of intranasal application of obidoxime (OBD) to saline in the control groups. Intranasally administered OBD was effective in partially reducing paraoxon-induced acetylcholinesterase inhibition in the brain and substantially reduced seizure severity and duration. Further, intranasal OBD completely prevented mortality, which was 41% in the animals given standard treatment plus intranasal saline. Fluoro-Jade-B staining revealed extensive neuronal degeneration in the surviving saline-treated animals 24h after paraoxon administration, whereas no detectable degenerating neurons were observed in any of the animals given intranasal OBD 30min before or 5min after paraoxon administration. These findings demonstrate that intranasally administered oximes bypass the BBB more effectively than those administered peripherally and provide an effective method for protecting the brain from organophosphates. The addition of intranasally administered oximes to the current treatment regimen for organophosphate poisoning would improve efficacy, reducing both brain damage and mortality.

Pharmacological treatment of organophosphorus insecticide poisoning: the old and the (possible) new

Despite being a major clinical and public health problem across the developing world, responsible for at least 5 million deaths over the last three decades, the clinical care of patients with organophosphorus (OP) insecticide poisoning has little improved over the last six decades. We are still using the same two antidotes - atropine and oximes - that first came into clinical use in the late 1950s. Clinical research in South Asia has shown how improved regimens of atropine can prevent deaths. However, we are still unsure about which patients are most likely to benefit from the use of oximes. Supplemental antidotes, such as magnesium, clonidine and sodium bicarbonate, have all been proposed and studied in small trials without production of definitive answers. Novel antidotes such as nicotinic receptor antagonists, beta-adrenergic agonists and lipid emulsions are being studied in large animal models and in pilot clinical trials. Hopefully, one or more of these affordable and already licensed antidotes will find their place in routine clinical care. However, the large number of chemically diverse OP insecticides, the varied poisoning they produce and their varied response to treatment might ultimately make it difficult to determine definitively whether these antidotes are truly effective. In addition, the toxicity of the varied solvents and surfactants formulated with the OP active ingredients complicates both treatment and studies. It is possible that the only effective way to reduce deaths from OP insecticide poisoning will be a steady reduction in their agricultural use worldwide.

Neuroprotection Against Diisopropylfluorophosphate in Acute Hippocampal Slices

Diisopropylfluorophosphate (DFP) is an irreversible inhibitor of acetylcholine esterase and a surrogate of the organophosphorus (OP) nerve agent sarin. The neurotoxicity of DFP was assessed as a reduction of population spike (PS) area elicited by synaptic stimulation in acute hippocampal slices. Two classical antidotes, atropine, and pralidoxime, and two novel antidotes, 4R-cembranotriene-diol (4R) and a caspase nine inhibitor, were tested. Atropine, pralidoxime, and 4R significantly protected when applied 30 min after DFP. The caspase inhibitor was neuroprotective when applied 5-10 min before or after DFP, suggesting that early synaptic apoptosis is responsible for the loss of PSs. It is likely that apoptosis starts at the synapses and, if antidotes are not applied, descends to the cell bodies, causing death. The acute slice is a reliable tool for mechanistic studies, and the assessment of neurotoxicity and neuroprotection with PS areas is, in general, pharmacologically congruent with in vivo results and predicts the effect of drugs in vivo. 4R was first found to be neuroprotective in slices and later we demonstrated that 4R is neuroprotective in vivo. The mechanism of neurotoxicity of OPs is not well understood, and there is a need for novel antidotes that could be discovered using acute slices.

Respiratory complications of organophosphorus nerve agent and insecticide poisoning. Implications for respiratory and critical care

Organophosphorus (OP) compound poisoning is a major global public health problem. Acute OP insecticide self-poisoning kills over 200,000 people every year, the majority from self-harm in rural Asia. Highly toxic OP nerve agents (e.g., sarin) are a significant current terrorist threat, as shown by attacks in Damascus during 2013. These anticholinesterase compounds are classically considered to cause an acute cholinergic syndrome with decreased consciousness, respiratory failure, and, in the case of insecticides, a delayed intermediate syndrome that requires prolonged ventilation. Acute respiratory failure, by central and peripheral mechanisms, is the primary cause of death in most cases. However, preclinical and clinical research over the last two decades has indicated a more complex picture of respiratory complications after OP insecticide poisoning, including onset of delayed neuromuscular junction dysfunction during the cholinergic syndrome, aspiration causing pneumonia and acute respiratory distress syndrome, and the involvement of solvents in OP toxicity. The treatment of OP poisoning has not changed over the last 50 years. However, a better understanding of the multiple respiratory complications of OP poisoning offers additional therapeutic opportunities.

Is the World Health Organization-recommended dose of pralidoxime effective in the treatment of organophosphorus poisoning? A randomized, double-blinded and placebo-controlled trial

Background:

Organophosphorus poisoning (OPP) is a major global public health problem. Pralidoxime has been used in a complimentary role to atropine for the management of OPP. World Health Organization (WHO) recommends use of pralidoxime but studies regarding its role have been inconclusive, ranging from being ineffective to harmful or beneficial.

Materials and Methods:

The present study was undertaken to evaluate the effectiveness of pralidoxime. Eddleston's study was the most compelling factor for our study, as he showed worst outcomes using pralidoxime. Our practice of continuous use of pralidoxime was based on the WHO guidelines and the study by Pawar (2006), which showed better outcome with higher doses of pralidoxime. These conflicting results suggested that a re-evaluation of its use in our clinical practice was indicated.

Results:

There was no difference in mortality rates, hemodynamic parameters and atropine requirements between the AP and A groups. Mean duration of ventilation (3.6 ± 4.6 in AP group vs. 3.6 ± 4.4 in A group) and Intensive Care Unit stay (7.1 ± 5.4 in AP group vs. 6.8 ± 4.7 in A group) was comparable. Serum sodium concentrations showed a correlation with mortality, with lower concentrations associated with better outcomes.

Conclusion:

The study suggests that add-on WHO-recommended pralidoxime therapy does not provide any benefit over atropine monotherapy. Adding pralidoxime does not seem to be beneficial and at the same time does not result in increased mortality rates. Our practice changed after completion of this study, and it has proven to be of significant benefit to patients who had to bear the expense of treatment.

Organophosphorus and carbamate insecticide poisoning

Both organophosphorus (OP) and carbamate insecticides inhibit acetylcholinesterase (AChE), which results in accumulation of acetylcholine (ACh) at autonomic and some central synapses and at autonomic postganglionic and neuromuscular junctions. As a consequence, ACh binds to, and stimulates, muscarinic and nicotinic receptors, thereby producing characteristic features. With OP insecticides (but not carbamates), "aging" may also occur by partial dealkylation of the serine group at the active site of AChE; recovery of AChE activity requires synthesis of new enzyme in the liver. Relapse after apparent resolution of cholinergic symptoms has been reported with OP insecticides and is termed the intermediate syndrome. This involves the onset of muscle paralysis affecting particularly upper-limb muscles, neck flexors, and cranial nerves some 24-96 hours after OP exposure and is often associated with the development of respiratory failure. OP-induced delayed neuropathy results from phosphorylation and subsequent aging of at least 70% of neuropathy target esterase. Cramping muscle pain in the lower limbs, distal numbness, and paresthesiae are followed by progressive weakness, depression of deep tendon reflexes in the lower limbs and, in severe cases, in the upper limbs. The therapeutic combination of oxime, atropine, and diazepam is well established experimentally in the treatment of OP pesticide poisoning. However, there has been controversy as to whether oximes improve morbidity and mortality in human poisoning. The explanation may be that the solvents in many formulations are primarily responsible for the high morbidity and mortality; oximes would not be expected to reduce toxicity in these circumstances. even if given in appropriate dose.

Clinical features of organophosphate poisoning: A review of different classification systems and approaches

PURPOSE

The typical toxidrome in organophosphate (OP) poisoning comprises of the Salivation, Lacrimation, Urination, Defecation, Gastric cramps, Emesis (SLUDGE) symptoms. However, several other manifestations are described. We review the spectrum of symptoms and signs in OP poisoning as well as the different approaches to clinical features in these patients.

MATERIALS AND METHODS

Articles were obtained by electronic search of PubMed(®) between 1966 and April 2014 using the search terms organophosphorus compounds or phosphoric acid esters AND poison or poisoning AND manifestations.

RESULTS

Of the 5026 articles on OP poisoning, 2584 articles pertained to human poisoning; 452 articles focusing on clinical manifestations in human OP poisoning were retrieved for detailed evaluation. In addition to the traditional approach of symptoms and signs of OP poisoning as peripheral (muscarinic, nicotinic) and central nervous system receptor stimulation, symptoms were alternatively approached using a time-based classification. In this, symptom onset was categorized as acute (within 24-h), delayed (24-h to 2-week) or late (beyond 2-week). Although most symptoms occur with minutes or hours following acute exposure, delayed onset symptoms occurring after a period of minimal or mild symptoms, may impact treatment and timing of the discharge following acute exposure. Symptoms and signs were also viewed as an organ specific as cardiovascular, respiratory or neurological manifestations. An organ specific approach enables focused management of individual organ dysfunction that may vary with different OP compounds.

CONCLUSIONS

Different approaches to the symptoms and signs in OP poisoning may better our understanding of the underlying mechanism that in turn may assist with the management of acutely poisoned patients.

Reversible cholinesterase inhibitors as pre-treatment for exposure to organophosphates: assessment using azinphos-methyl

Pre-treatment with reversible acetylcholinesterase (AChE) inhibitors before organophosphorous compound (OPC) exposure can reduce OPC-induced mortality. However, pyridostigmine, the only substance employed for such prophylaxis, is merely efficacious against a limited number of OPCs. In search of more efficacious and broad-range alternatives, we have compared in vivo the ability of five reversible AChE inhibitors (pyridostigmine, physostigmine, ranitidine, tacrine and K-27) to reduce mortality induced by the OPC azinphos-methyl. Protection was quantified using Cox analysis by determining the relative risk (RR) of death in rats that were administered these AChE inhibitors in equitoxic dosage (25% of LD01) 30 min before azinphos-methyl exposure. Azinphos-methyl-induced mortality was significantly reduced by all five tested compounds as compared with the reference group that was only exposed to azinphos-methyl without prior pre-treatment (RR = 1). The most efficacious prophylactic agents were K-27 (RR = 0.15) and physostigmine (RR = 0.21), being significantly more efficacious than ranitidine (RR = 0.62) and pyridostigmine (RR = 0.37). Pre-treatment with tacrine (RR = 0.29) was significantly more efficacious than pre-treatment with ranitidine, but the difference between tacrine and pyridostigmine was not significant. Our results indicate that prophylactic administration of the oxime K-27 may be a promising alternative in cases of imminent OPC exposure.

Animal models that best reproduce the clinical manifestations of human intoxication with organophosphorus compounds

The translational capacity of data generated in preclinical toxicological studies is contingent upon several factors, including the appropriateness of the animal model. The primary objectives of this article are: 1) to analyze the natural history of acute and delayed signs and symptoms that develop following an acute exposure of humans to organophosphorus (OP) compounds, with an emphasis on nerve agents; 2) to identify animal models of the clinical manifestations of human exposure to OPs; and 3) to review the mechanisms that contribute to the immediate and delayed OP neurotoxicity. As discussed in this study, clinical manifestations of an acute exposure of humans to OP compounds can be faithfully reproduced in rodents and nonhuman primates. These manifestations include an acute cholinergic crisis in addition to signs of neurotoxicity that develop long after the OP exposure, particularly chronic neurologic deficits consisting of anxiety-related behavior and cognitive deficits, structural brain damage, and increased slow electroencephalographic frequencies. Because guinea pigs and nonhuman primates, like humans, have low levels of circulating carboxylesterases-the enzymes that metabolize and inactivate OP compounds-they stand out as appropriate animal models for studies of OP intoxication. These are critical points for the development of safe and effective therapeutic interventions against OP poisoning because approval of such therapies by the Food and Drug Administration is likely to rely on the Animal Efficacy Rule, which allows exclusive use of animal data as evidence of the effectiveness of a drug against pathologic conditions that cannot be ethically or feasibly tested in humans.

Parenteral organophosphorus poisoning in a rural emergency department: a case report

BACKGROUND

Poisoning is a common presentation in the emergency department. Oral exposures to organophosphorus compounds are especially frequent in rural and agricultural regions of South Asia and throughout the developing world.

CASE PRESENTATION

Here we report a case of deliberate self-harm with an organophosphorus pesticide via the relatively uncommon parenteral route. A young woman injected herself with chlorpyriphos. Although the cholinergic effects were mild, cellulitis and abscess development were noted as a result.

CONCLUSION

Resource limited agricultural countries like Nepal present health care workers with numerous challenges in poisoning management. This case represents a rare but potentially morbid method of agrochemical poison exposure.