Comparison of current recommended regimens of atropinization in organophosphate poisoning

Sublingual administration of atropine eye drops for treating organophosphorus poisoning

An 89-year-old patient with fenitrothion toxicity received sublingual atropine eye drops, reducing the intravenous atropine requirement. This alternative method enabled rapid rehabilitation, and he walked unaided, leading to discharge.

Atropine sulfate as a continuous intravenous infusion for the treatment of organophosphate toxicity in a cat

Case summary

A 1-year-old male neutered domestic shorthair cat presented on an emergency basis with clinical signs suspected to be secondary to organophosphate (OP) toxicity. The control of clinical abnormalities (bradycardia, obtundation, tachypnea, anorexia) was achieved using high-dose continuous rate intravenous infusion (CRI) of atropine sulfate (maximum rate 0.1 mg/kg/h). After 5 days of hospitalization, the patient made a full clinical recovery without the development of atropine toxicity, intermediate syndrome or delayed polyneuropathy at 4 weeks after discharge.

Relevance and novel information

Treatment of OP toxicity in cats is sparsely reported in veterinary literature. Current standards of treatment and published protocols recommend the use of atropine sulfate as intermittent boluses for the treatment of muscarinic signs of toxicity; however, there is a paucity of information regarding the safety and efficacy of atropine sulfate as a CRI for severe toxicosis as described in humans. This report includes the first published case using such a treatment protocol in a cat.

Management of Organophosphorus Poisoning: Standard Treatment and Beyond

Organophosphorus (OP) compounds remain a leading cause of self-poisoning and mortality, especially in South East Asia, China, and Africa. Organophosphorus causes an acute cholinergic syndrome by inhibiting acetylcholinesterase. Atropine remains the mainstay of treatment, but recently some promising therapies are in the pipeline. Oximes are used widely in the management of organophosphorus poisoning, however clinical efficacy remains to be established. Magnesium sulfate, calcium channel blockers (nimodipine), plasma alkalinizing agents, β-2 agonists, nicotinic receptor antagonists, clonidine, and lipid emulsions are promising treatment alternatives. However, large phase III trials are required to establish their efficacy.

Synergistic enhancement of the emergency treatment effect of organophosphate poisoning by a supramolecular strategy

Poisoning by organophosphorus agents (OPs) is a serious public health issue across the world. These compounds irreversibly inhibit acetylcholinesterase (AChE), resulting in the accumulation of acetylcholine (ACh) and overstimulation of ACh receptors. A supramolecular detoxification system (SDS) has been designed with a view to deliver pyridine-2-aldoxime methochloride (PAM) with a synergistic inhibition effect on the ACh-induced hyperstimulation through host-guest encapsulation. NMR and fluorescence titration served to confirm the complexation between carboxylatopillar[6]arene (CP6A) and PAM as well as ACh with robust affinities. Patch-clamp studies proved that CP6A could exert an inhibition effect on the ACh-induced hyperstimulation of ACh receptors. Support for the feasibility of this strategy came from fluorescence imaging results. In vivo studies revealed that complexation by CP6A serves to increase the AChE reactivation efficiency of PAM. The formation of the PAM/CP6A complex contributed to enhance in a statistically significant way the ability of PAM not only to relieve symptoms of seizures but also to improve the survival ratio in paraoxon-poisoned model rats. These favorable findings are attributed to synergistic effects that PAM reactivates AChE to hydrolyze ACh and excess ACh is encapsulated in the cavity of CP6A to relieve cholinergic crisis symptoms.

Comparative physiology and efficacy of atropine and scopolamine in sarin nerve agent poisoning

Anticholinergic treatment is key for effective medical treatment of nerve agent exposure. Atropine is included at a 2 mg intramuscular dose in so-called autoinjectors designed for self- and buddy-aid. As patient cohorts are not available, predicting and evaluating the efficacy of medical countermeasures relies on animal models. The use of atropine as a muscarinic antagonist is based on efficacy achieved in studies in a variety of species. The dose of atropine administered varies considerably across these studies. This is a complicating factor in the prediction of efficacy in the human situation, largely because atropine dosing also influences therapeutic efficacy of oximes and anticonvulsants generally part of the treatment administered. To improve translation of efficacy of dosing regimens, including pharmacokinetics and physiology provide a promising approach. In the current study, pharmacokinetics and physiological parameters obtained using EEG and ECG were assessed in naïve rats and in sarin-exposed rats for two anticholinergic drugs, atropine and scopolamine. The aim was to find a predictive parameter for therapeutic efficacy. Scopolamine and atropine showed a similar bioavailability, but brain levels reached were much higher for scopolamine. Scopolamine exhibited a dose-dependent loss of beta power in naïve animals, whereas atropine did not show any such central effect. This effect was correlated with an enhanced anticonvulsant effect of scopolamine compared to atropine. These findings show that an approach including pharmacokinetics and physiology could contribute to improved dose scaling across species and assessing the therapeutic potential of similar anticholinergic and anticonvulsant drugs against nerve agent poisoning.

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.

COPD and asthma therapeutics for supportive treatment in organophosphate poisoning

Context: Nerve agents like sarin or VX have repeatedly been used in military conflicts or homicidal attacks, as seen in Syria or Malaysia 2017. Together with pesticides, nerve agents assort as organophosphorus compounds (OP), which inhibit the enzyme acetylcholinesterase. To counteract subsequent fatal symptoms due to acetylcholine (ACh) accumulation, oximes plus atropine are administered, a regimen that lacks efficacy in several cases of OP poisoning. New therapeutics are in development, but still need evaluation before clinical employment. Supportive treatment with already approved drugs presents an alternative, whereby compounds from COPD and asthma therapy are likely options. A recent pilot study by Chowdhury et al. included β2-agonist salbutamol in the treatment of OP-pesticide poisoned patients, yielding ambiguous results concerning the addition. Here, we provide experimental data for further investigations regarding the value of these drugs in OP poisoning. Methods: By video-microscopy, changes in airway area were analyzed in VX-poisoned rat precision cut lung slices (PCLS) after ACh-induced airway contraction and subsequent application of selected anticholinergics/β2-agonists. Results: Glycopyrrolate and ipratropium efficiently antagonized an ACh-induced airway contraction in VX-poisoned PCLS (EC₅₀ glycopyrrolate 15.8 nmol/L, EC₅₀ ipratropium 2.3 nmol/L). β2-agonists formoterol and salbutamol had only negligible effects when solely applied in the same setting. However, combination of formoterol or salbutamol with low dosed glycopyrrolate or atropine led to an additive effect compared to the sole application [50.6 ± 8.8% airway area increase after 10 nmol/L formoterol +1 nmol/L atropine versus 11.7 ± 9.2% (10 nmol/L formoterol) or 8.6 ± 5.9% (1 nmol/L atropine)]. Discussion: We showed antagonizing effects of anticholinergics and β2-agonists on ACh-induced airway contractions in VX-poisoned PCLS, thus providing experimental data to support a prospective comprehensive clinical study. Conclusions: Our results indicate that COPD and asthma therapeutics could be a valuable addition to the treatment of OP poisoning.

Novel Clinical Toxicology and Pharmacology of Organophosphorus Insecticide Self-Poisoning

Organophosphorus insecticide self-poisoning is a major global health problem, killing over 100,000 people annually. It is a complex multi-organ condition, involving the inhibition of cholinesterases, and perhaps other enzymes, and the effects of large doses of ingested solvents. Variability between organophosphorus insecticides—in lipophilicity, speed of activation, speed and potency of acetylcholinesterase inhibition, and in the chemical groups attached to the phosphorus—results in variable speed of poisoning onset, severity, clinical toxidrome, and case fatality. Current treatment is modestly effective, aiming only to reactivate acetylcholinesterase and counter the effects of excess acetylcholine at muscarinic receptors. Rapid titration of atropine during resuscitation is lifesaving and can be performed in the absence of oxygen. The role of oximes in therapy remains unclear. Novel antidotes have been tested in small trials, but the great variability in poisoning makes interpretation of such trials difficult. More effort is required to test treatments in adequately powered studies.

A simple and highly effective catalytic nanozyme scavenger for organophosphorus neurotoxins

A simple and highly efficient catalytic scavenger of poisonous organophosphorus compounds, based on organophosphorus hydrolase (OPH, EC 3.1.8.1), is produced in aqueous solution by electrostatic coupling of the hexahistidine tagged OPH (His₆-OPH) and poly(ethylene glycol)-b-poly(l-glutamic acid) diblock copolymer. The resulting polyion complex, termed nano-OPH, has a spherical morphology and a diameter from 25nm to 100nm. Incorporation of His₆-OPH in nano-OPH preserves catalytic activity and increases stability of the enzyme allowing its storage in aqueous solution for over a year. It also decreases the immune and inflammatory responses to His₆-OPH in vivo as determined by anti-OPH IgG and cytokines formation in Sprague Dawley rats and Balb/c mice, respectively. The nano-OPH pharmacokinetic parameters are improved compared to the naked enzyme suggesting longer blood circulation after intravenous (iv) administrations in rats. Moreover, nano-OPH is bioavailable after intramuscular (im), intraperitoneal (ip) and even transbuccal (tb) administration, and has shown ability to protect animals from exposure to a pesticide, paraoxon and a warfare agent, VX. In particular, a complete protection against the lethal doses of paraoxon was observed with nano-OPH administered iv and ip as much as 17h, im 5.5h and tb 2h before the intoxication. Further evaluation of nano-OPH as a catalytic bioscavenger countermeasure against organophosphorus chemical warfare agents and pesticides is warranted.

Possible role for anisodamine in organophosphate poisoning

In cases of organophosphate poisoning, patients are treated with a combination of antidotes. In addition to these poison-directed antidotes, patients may require extra oxygen and artificial ventilation; other modalities may also be needed due to the wide range of toxic effects. Anisodamine is a belladonna alkaloid, and like other drugs from this family is non subtype-selective muscarinic, and a nicotinic cholinoceptor antagonist, which has been employed in traditional Chinese medicine. As a muscarinic antagonist, it displays similar pharmacological effects to atropine and scopolamine. However, anisodamine is not only less potent than atropine and scopolamine but also less toxic. Current in vitro and animal model studies have demonstrated that anisodamine has protective effects in a variety of diseases. Organophosphate poisoning involves not only the central and peripheral nervous systems, but also the cardiac and respiratory systems, as well as activation of inflammatory processes and oxidative stress. Therefore, the anticholinergic and additional activities of anisodamine appear to be relevant and justify its consideration as an addition to the existing remedies. However, more research is needed, as at present data on the role of anisodamine in the management of organophosphate poisoning are limited. Here, we review the beneficial effects of anisodamine on processes relevant to organophosphate poisoning.

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.

Developments in alternative treatments for organophosphate poisoning

Organophosphosphates (OPs) are highly effective acetylcholinesterase (AChE) inhibitors that are used worldwide as cheap, multi-purpose insecticides. OPs are also used as chemical weapons forming the active core of G-series and V-series chemical agents including tabun, sarin, soman, cyclosarin, VX, and their chemical analogs. Human exposure to any of these compounds leads to neurotoxic accumulation of the neurotransmitter acetylcholine, resulting in abnormal nerve function and multiple secondary health complications. Suicide from deliberate exposure to OPs is particularly prevalent in developing countries across the world and constitutes a major global health crisis. The prevalence and accessible nature of OP compounds within modern agricultural spheres and concern over their potential use in biochemical weapon attacks have incentivized both government agencies and medical researchers to enact stricter regulatory policies over their usage and to begin developing more proactive medical treatments in cases of OP poisoning. This review will discuss the research undertaken in recent years that has investigated new supplementary drug options for OP treatment and support therapy, including progress in the development of enzymatic prophylaxis.