Oxime therapy and outcomes in human organophosphate poisoning: an evaluation using meta-analytic techniques

Atypical organophosphate poisoning and a successful case of prolonged intubation in a low-resource newly developed intensive care unit in rural Zambia

Organophosphate poisoning is a common, under-reported cause of attempted and completed suicide worldwide. Following the resolution of the acute cholinergic syndrome, patients may develop respiratory muscle and proximal limb weakness, known as intermediate syndrome. A young man was brought to our rural hospital unconscious, in extremis, due to organophosphate pesticide poisoning. He developed atypical intermediate syndrome with global paralysis, persistent fasciculations and prolonged cholinergic symptoms, differing from the recognised presentation. He was intubated for fifteen days in our newly developed intensive care unit. Limited treatment options and the absence of blood gases, electrolyte testing, ECGs, invasive monitoring and imaging, in conjunction with regular disruptions to electricity and oxygen, and complications including seizures and pneumonia, all made this prolonged intubation an ambitious and challenging endeavour. We offer learning points for the acute physician and rural intensivist, and a summary of our reflections and hints for best care when adapting to a resource-limited setting.

Protective Activity of Novel Hydrophilic Synthetic Neurosteroids on Organophosphate Status Epilepticus-induced Chronic Epileptic Seizures, Non-Convulsive Discharges, High-Frequency Oscillations, and Electrographic Ictal Biomarkers

Nerve agents and organophosphates (OP) are neurotoxic chemicals that induce acute seizures, status epilepticus (SE), and mortality. Long-term neurologic and neurodegenerative effects manifest months to years after OP exposure. Current benzodiazepine anticonvulsants are ineffective in preventing such long-term neurobehavioral and neuropathological changes. New and effective anticonvulsants are needed for OP intoxication, especially for mitigating the long-term sequelae after acute exposure. We developed neurosteroids as novel anticonvulsants and neuroprotectants in OP exposure models. In this study, we evaluated the long-term efficacy of novel synthetic neurosteroids in preventing the development of chronic epilepsy and hyperexcitable ictal events in a rat OP model of SE. Rats were exposed to the OP nerve agent surrogate diisopropylfluorophosphate (DFP), and the experimental groups were treated with the synthetic neurosteroid valaxanolone (VX) or lysaxanolone (LX) 40 minutes post-exposure in conjunction with midazolam. Video-electroencephalography was monitored for two months to assess spontaneous recurrent seizures (SRS), epileptiform discharges, interictal spikes, and high-frequency oscillations (HFOs). Within 60 days of DFP exposure, rats developed chronic epilepsy characterized by frequent SRS, epileptiform discharges, and HFOs. LX treatment was associated with a dose-dependent reduction of epilepsy occurrence and overall seizure burden with a significant decrease in SRS and epileptiform discharges. It also significantly reduced the occurrence of epileptic biomarkers of HFOs and interictal spikes, indicating potential disease-modifying activity. Similarly, the neurosteroid analog VX also significantly attenuated SRS, discharges, HFOs, and ictal events. These results demonstrate the long-term protective effects of synthetic neurosteroids in the OP-exposed post-SE model, indicating their disease-modifying potential to prevent epilepsy and ictal abnormalities. SIGNIFICANCE STATEMENT: The effects of nerve agents and organophosphate (OP) exposure are persistent, and survivors suffer from a number of devastating, chronic neurological dysfunctions. Currently, there is no specific therapy for preventing this disastrous impact of OP exposure. We propose synthetic neurosteroids that activate tonic inhibition provide viable options for preventing the long-term neurological effects of OP intoxication. The results from this study reveal the disease-modifying potential of two novel synthetic neurosteroids in preventing epileptogenesis and chronic epileptic seizures after OP-induced SE.

The role of a combination of N-acetylcysteine and magnesium sulfate as adjuvants to standard therapy in acute organophosphate poisoning: A randomized controlled trial

Background

Mortality in acute organophosphate (OP) poisoning remains high despite current standard therapy with atropine and oximes. Due to dose-limiting side effects of atropine, novel therapies are targeting other putative mechanisms of injury, including oxidative damage, to reduce atropine dosage.

Objectives

N-acetylcysteine (NAC) and magnesium sulfate (MgSO₄) have different mechanisms of actions and should act synergistically in OP poisoning. In this study, we wanted to evaluate whether this novel combination, used as an adjuvant to standard care, could improve clinical outcomes.

Methods

The study was conducted in the Emergency Department and ICU of AIIMS Bhubaneswar (a tertiary care center and government teaching institute) between July 2019 and July 2021. Eighty-eight adult patients with history and clinical features of acute OP poisoning were randomly allocated (1:1) into two groups. The Study group received 600 mg NAC via nasogastric tube thrice daily for 3 days plus a single dose of 4 g Inj. MgSO₄ IV on first day and the Control group received suitably matched placebo (double-blinding) - in addition to standard care in both the groups. The primary outcome measure was to compare the total dose of Inj. Atropine required (cumulative over the entire treatment duration) between the control group and the study group receiving NAC and MgSO₄. The secondary outcome measures were lengths of ICU and hospital stays, need and duration of mechanical ventilation, the differences in BuChE activity, oxidative stress biomarkers - MDA and GSH levels, the incidences of adverse effects including delayed sequalae like intermediate syndrome and OPIDN, and comparison of mortality between the two groups.

Results

Data from 43 patients in Control and 42 patients in Study group was finally analyzed. The baseline parameters were comparable. Total atropine requirements were lower in the Study group [175.33 ± 81.25 mg (150.01-200.65)] compared to the Control [210.63 ± 102.29 mg (179.15-242.11)] [Mean ± SD (95% CI)], but was not statistically significant. No significant differences in any of the other clinical or biochemical parameters were noted.

Conclusion

The N-acetylcysteine and MgSO₄ combination as adjuvants failed to significantly reduce atropine requirements, ICU/hospital stay, mechanical ventilatory requirements, mortality and did not offer protection against oxidative damage.

Clinical manifestations, laboratory findings, treatment and outcome of acute organophosphate or carbamate intoxication in 39 cats

BACKGROUND

Organophosphates and carbamates are important sources of intoxication for humans and animals. However, large-scale studies of these intoxications in cats are unavailable.

METHODS

The medical records of 39 cats presented to a veterinary teaching hospital with acute organophosphate or carbamate intoxication were reviewed retrospectively.

RESULTS

Mortality in intoxicated cats was 15%. Low respiratory rate and low rectal temperature at presentation were associated with death. Other common clinical signs included weakness, ataxia, apathy, recumbency, anorexia and bradycardia, but these were unassociated with the outcome. The common biochemical abnormalities included decreased serum butyryl-choline esterase activity, acidaemia, hypercarbaemia and total hypocalcaemia, and increased creatine kinase activity and total plasma protein concentration. There were no significant differences in haematological, biochemical and blood gas analytes between survivors and non-survivors. Common medications and treatments included 2-pyridine aldoxime methyl-chloride-pralidoxime (2-PAM) (74%), metoclopramide (64%), antibiotics (64%), diphenhydramine (59%) and atropine sulphate (54%). There were no significant drug and treatment differences between survivors and non-survivors. The secondary complications of the intoxication included pneumonia (10%), acute kidney injury (10%) and pancreatitis (8%).

CONCLUSIONS

Acute cholinergic crisis due to organophosphate or carbamate intoxication has a fair prognosis in cats. Low respiratory rate and low rectal temperature at presentation were associated with death. The most commonly used specific medications in this study included 2-PAM, diphenhydramine and atropine sulphate.

Laryngeal Dysfunction in Acute Organophosphorus and Carbamate Poisoning

Background

Organophosphorus (OP) and carbamate pesticides are widely used for crop protection. We describe the spectrum of laryngeal abnormalities in patients admitted to the intensive care unit (ICU) with acute OP and carbamate poisoning as there is limited information on it.

Materials and methods

Consecutive patients admitted to the ICU with acute OP and carbamate poisoning over 20 months (December 2014–July 2016) were recruited. Patients were followed up post-discharge if they had undergone tracheostomy or developed hoarseness of voice or stridor following extubation. Asymptomatic individuals who consented underwent laryngoscopy after ICU discharge. The primary outcome was the development of laryngeal dysfunction. Other outcomes included length of stay, need for ventilation, mortality, tracheostomy, and time to decannulation of tracheostomy.

Results

Of the 136 patients recruited, 71 (52%) underwent laryngoscopy. The overall mortality rate was 9.6%. Of the 71 patients who underwent laryngoscopy, 18 had abnormal findings, which included unilateral or bilateral vocal cord paresis or palsy (n = 14) and/or aspiration (n = 9), subglottic stenosis (n = 1), tracheal stenosis (n = 1), or arytenoid granuloma (n = 1). Laryngeal dysfunction was associated with the ingestion of a dimethyl OP compound (p = 0.04) and quantum consumed (p <0.001). Patients with laryngeal dysfunction had significantly (p = 0.004) longer hospital stay (19.1 ± 10.7 vs 11.8 ± 8.3 days).

Conclusion

Laryngeal dysfunction is not uncommon in OP and carbamate poisoning and is associated with the ingestion of larger quantity of a dimethyl OP compound and longer hospital stay. Otorhinolaryngologists could be involved early to help identify these abnormalities and initiate an appropriate treatment to ensure a functional voice and good airway.

How to cite this article

Mani GS, Mathews SS, Victor P, Peter JV, Yadav B, Albert RRA. Laryngeal Dysfunction in Acute Organophosphorus and Carbamate Poisoning. Indian J Crit Care Med 2022;26(2):167–173.

Adrenaline is effective in reversing the inadequate heart rate response in atropine treated organophosphorus and carbamate poisoning

BACKGROUND

In acute organophosphorus (OP) or carbamate poisoning, some patients require high dose atropine to counteract the effects on heart rate (HR) and blood pressure (BP). This study describes the factors associated with high dose atropine therapy and the use of adrenaline to reverse the inadequate HR response to atropine.

METHODS

Consecutive patients admitted to the intensive care unit (ICU) were prospectively recruited. Demographic data, treatment and outcomes of patients who failed to achieve target HR (100/min) or systolic BP >90 mm Hg with either a cumulative atropine dose of 100-mg within 6-h following admission or an infusion of 30 mg/h for at least 3-h were compared with patients who achieved the targets. Factors associated with high dose atropine therapy were explored using logistic regression analysis and expressed as odds ratio (OR) with 95% confidence intervals (CIs).

RESULTS

Of the 181 patients admitted with OP or carbamate poisoning, 155 patients fulfilled inclusion criteria. The mean (SD) age was 35.7 (15.8) years; admission APACHE-II score was 14.6 (7.5). Heart rate and/or BP target was not achieved in 13.6%. In these patients, target HR was achieved after adding adrenaline infusion at 2-4 μg/min. Ventilation duration (11.6 ± 6.3 vs. 8.4 ± 6.9 days, p = 0.05) and ICU stay (12.3 ± 5.8 vs. 8.9 ± 5.8 days, p = 0.01) were longer in patients requiring high dose atropine when compared with others. On multivariate logistic regression analysis, shorter time to presentation to hospital (p = 0.04) was associated with need for high dose atropine. Overall mortality was 9% and similar in both groups (p = 0.41).

CONCLUSIONS

High dose atropine therapy is required in a subset of patients with OP and carbamate poisoning and was associated with longer ventilation duration and ICU stay. Adrenaline infusion improved hemodynamics in these patients.

Efficacy of fresh frozen plasma transfusion in comparison with conventional regimen in organophosphate poisoning treatment: a meta-analysis study

OBJECTIVE

To evaluating the efficacy of fresh frozen plasma (FFP) in comparison with conventional regimen in the treatment of organophosphate (OP) poisoning.

METHODS

PubMed, ScopeMed, Cochrane, Scopus, and Google Scholar databases were searched. The search strategy used the following key words "organophosphate" and "poisoning or toxicity", "(atropine and oxime)", "fresh frozen plasma", "clinical trial", "outcome". The treatment with atropine or/and oxime was considered conventional therapy. The length of hospitalization, the length of ICU admission, need for mechanical ventilation and its duration, clinical recovery point, choline esterase level, mortality rate, and intermediate syndrome (IMS) occurrence were the key outcomes of interest. Databases were searched during the period of 2003-2019. Five studies were included in the analysis.

RESULTS

Pooling of data showed that the relative risk (RR) of mortality in OP poisoning for five included trials comparing FFP-treated group with conventional regimen therapy was [0.563 (95% CI (0.252, 1.255)]. The summary of RR for IMS in two studies was [RR: 1.34, 95% CI (0.655, 2.742)]. In addition, there was a non-significant mean difference (MD) in hospital stay [MD: -0.106, 95% CI (-0.434, 0.223)] in three included trials. A significant MD was observed in the length of ICU admission in two trials between FFP-treated group compared to the conventional treatment group [MD: -2.672, 95% CI (-4.189, -1.154)], but after random effects meta-analysis, the changes were not significant [MD: -2.015, 95% CI (-6.308, 2.277)]. The summary of fixed-effect meta-analysis for choline esterase level in three trails was [MD: -0.117, 95% CI (-0.468, 0.234)]. The RR of ventilation requirement for two included trials in the FFP-treated group comparing to the conventional regimen therapy was [0.84, 95% CI (0.691, 1.022)] while for ventilation duration in two studies was [MD: -0.183, 95% CI (-0.567, 0.201)].

CONCLUSION

The addition of FFP to conventional therapy did not improve the outcomes of mortality, IMS, hospital length of stay, cholinesterase levels, need or duration of mechanical ventilation, and only the length of ICU stay could affect in the treated group.

Organophosphorus compounds and oximes: a critical review

Organophosphorus (OP) pesticides and nerve agents still pose a threat to the population. Treatment of OP poisoning is an ongoing challenge and burden for medical services. Standard drug treatment consists of atropine and an oxime as reactivator of OP-inhibited acetylcholinesterase and is virtually unchanged since more than six decades. Established oximes, i.e. pralidoxime, obidoxime, TMB-4, HI-6 and MMB-4, are of insufficient effectiveness in some poisonings and often cover only a limited spectrum of the different nerve agents and pesticides. Moreover, the value of oximes in human OP pesticide poisoning is still disputed. Long-lasting research efforts resulted in the preparation of countless experimental oximes, and more recently non-oxime reactivators, intended to replace or supplement the established and licensed oximes. The progress of this development is slow and none of the novel compounds appears to be suitable for transfer into advanced development or into clinical use. This situation calls for a critical analysis of the value of oximes as mainstay of treatment as well as the potential and limitations of established and novel reactivators. Requirements for a straightforward identification of superior reactivators and their development to licensed drugs need to be addressed as well as options for interim solutions as a chance to improve the therapy of OP poisoning in a foreseeable time frame.

An Appraisal of Antidotes' Effectiveness: Evidence of the Use of Phyto-Antidotes and Biotechnological Advancements

Poisoning is the greatest source of avoidable death in the world and can result from industrial exhausts, incessant bush burning, drug overdose, accidental toxication or snake envenomation. Since the advent of Albert Calmette’s cobra venom antidote, efforts have been geared towards antidotes development for various poisons to date. While there are resources and facilities to tackle poisoning in urban areas, rural areas and developing countries are challenged with poisoning management due to either the absence of or inadequate facilities and this has paved the way for phyto-antidotes, some of which have been scientifically validated. This review presents the scope of antidotes’ effectiveness in different experimental models and biotechnological advancements in antidote research for future applications. While pockets of evidence of the effectiveness of antidotes exist in vitro and in vivo with ample biotechnological developments, the utilization of analytic assays on existing and newly developed antidotes that have surpassed the proof of concept stage, as well as the inclusion of antidote’s short and long-term risk assessment report, will help in providing the required scientific evidence(s) prior to regulatory authorities’ approval.

The antidotes atropine and pralidoxime distinctively recover cardiorespiratory components impaired by acute poisoning with chlorpyrifos in rats

In a previous work we showed that the organophosphate pesticide (OP) chlorpyrifos (CPF) reduces the protective chemoreflex and baroreflex responses in rats. However, whether the antidotes atropine (ATR) and pralidoxime (2-PAM) are capable of restoring these reflex functions remains unexplored. Rats were poisoned with CPF (30 mg.kg^-1, i.p.) and one hour after the intoxication, ATR (10 mg.kg^-1, i.p.) and 2-PAM (40 mg.kg^-1, i.p.) were administrated separately or in combination. Cardiorespiratory parameters were recorded in awake rats 24 h after CPF. Systolic blood pressure (SBP) and heart rate (HR) variability and spontaneous baroreflex sensitivity (sBRS) were derived from undisturbed recordings (30 min), while chemoreflex was assessed through potassium cyanide (KCN) i.v. injections (10, 20, 40, 80 μg/rat). CPF poisoning increased SBP variability and low frequency/high frequency (LF/HF) ratio of the HR variability spectrum, indicating autonomic imbalance with increased cardiac sympathetic tone. sBRS was not changed. Treatment with 2-PAM restored SBP variability, whilst both antidotes increased LF/HF ratio. CPF poisoning reduced the hypertensive, bradycardic and tachypneic chemoreflex responses. Chemoreflex-induced hypertensive response was restored by 2-PAM treatment, while ATR recovered the bradycardic response. Both antidotes restored the chemoreflex tachypneic response. Our data show distinct effects of ATR and 2-PAM on cardiorespiratory parameters affected by OP poisoning. While 2-PAM rescued the chemoreflex hypertensive response, ATR reversed chemoreflex bradycardic dysfunction. Although 2-PAM clinical use is questioned in some countries, our data indicate that summation of effects of both antidotes appears beneficial on the cardiorespiratory system and peripheral chemoreflex function.

Clinical efficacy of intravenous infusion of atropine with micropump in combination with hemoperfusion on organophosphorus poisoning

Objective

To observe the clinical efficacy of intravenous infusion of atropine with micropump in combination with hemoperfusion on organophosphorus poisoning patients, and investigate the potential mechanism.

Methods

In this study, we enrolled 136 organophosphorus poisoning patients who received treatment in this hospital between January 2009 and December 2017, and they were divided into three groups according to the clinical treatment methods, i.e. Group A (comprehensive treatment with HP, n = 47), Group B (continuous intravenous infusion of atropine with micropump, n = 43) and Group C (regular intravenous infusion of atropine, n = 46). In addition to the close monitoring of vital signs, we recorded the atropinization time (min), cholinesterase reactivation time (h), total dose of atropine, recurrence, incidence rate of atropine poisoning (%), hospitalization time (d) and cure rate (%).

Results

In comparison with Group C, patients in Group A and B manifested more stable vital signs with lower total dose of atropine and incidence rate of atropine poisoning and shorter cholinesterase reactivation time, while the cure rate was remarkably increased (p < 0.05), and no significant differences were observed in atropinization time among three groups (p > 0.05). Compared to Group B and C, total dose of atropine in Group A was significantly decreased with obvious excellence in hospitalization time, reduction of complications and increases in cure rates (p < 0.05). Moreover, patients in Group A had the lowest mortality rate among three groups.

Conclusion

In treatment of organophosphorus poisoning patients, HP and continuous intravenous infusion of atropine using micropump can elevate the survival rate, reduce the incidence of adverse reaction, shorten the reactivation time of cholinesterase and decrease the incidence rate of complications, which are superior to the traditional treatment method.

Fasciculating toxicity

Organophosphorus (OP) compound poisoning with suicidal intent is common. It is one of the frequent cause for admission to hospital Emergencies and intensive care units in our region. We describe here a case of 19-year old girl who presented to the Emergency Department with atypical features of OP poisoning. She had perioral, tongue and lower limb fasciculations along with generalized muscle weakness with no or minimal muscarinic effects. OP poisoning with isolated nicotinic receptor mediated effect is often reported in children but in adult it is extremely rare. Based on history and clinical suspicion of nicotinic receptor mediated effect of OP, she was given intravenous atropine along with other supportive treatment. Patient got completely recovered from fasciculations and her motor weakness improved after 6 h of atropine therapy. Emergency physician should keep a high index of suspicion of isolated nicotinic and ganglionic mediated effect of OP and a trial of atropine should be given to the patient.

Antidotes in Poisoning

Introduction

Antidotes are agents that negate the effect of a poison or toxin. Antidotes mediate its effect either by preventing the absorption of the toxin, by binding and neutralizing the poison, antagonizing its end-organ effect, or by inhibition of conversion of the toxin to more toxic metabolites. Antidote administration may not only result in the reduction of free or active toxin level, but also in the mitigation of end-organ effects of the toxin by mechanisms that include competitive inhibition, receptor blockade or direct antagonism of the toxin.

Mechanism of action of antidotes

Reduction in free toxin level can be achieved by specific and non-specific agents that bind to the toxin. The most commonly used non-specific binding agent is activated charcoal. Specific binders include chelating agents, bioscavenger therapy and immunotherapy. In some situations, enhanced elimination can be achieved by urinary alkalization or hemadsorption. Competitive inhibition of enzymes (e.g. ethanol for methanol poisoning), enhancement of enzyme function (e.g. oximes for organophosphorus poisoning) and competitive receptor blockade (e.g. naloxone, flumazenil) are other mechanisms by which antidotes act. Drugs such as N-acetyl cysteine and sodium thiocyanate reduce the formation of toxic metabolites in paracetamol and cyanide poisoning respectively. Drugs such as atropine and magnesium are used to counteract the end-organ effects in organophosphorus poisoning. Vitamins such as vitamin K, folic acid and pyridoxine are used to antagonise the effects of warfarin, methotrexate and INH respectively in the setting of toxicity or overdose. This review provides an overview of the role of antidotes in poisoning.

How to cite this article

Chacko B, Peter JV. Antidotes in Poisoning. Indian J Crit Care Med 2019;23(Suppl 4):S241-S249.

Enzymatic detoxification of organophosphorus pesticides and related toxicants

Millions of cases of pesticide intoxication occur yearly and represent a public health problem. In addition, pesticide poisoning is the preferred suicidal method in rural areas. The use of enzymes for the treatment of intoxication due to organophosphorus pesticides was proposed decades ago. Several enzymes are able to transform organophosphorus compounds such as pesticides and nerve agents. Some specific enzymatic treatments have been proposed, including direct enzyme injection, liposome and erythrocytes carriers, PEGylated preparations and extracorporeal enzymatic treatments. Nevertheless, no enzymatic treatments are currently available. In this work, the use of enzymes for treating of organophosphorus pesticide intoxication is critically reviewed and the remaining challenges are discussed.

Chlorpyrifos-induced parkinsonian model in mice: Behavior, histopathology and biochemistry

INTRODUCTION

The aim of this study was to investigate the protective effect of caffeic acid phenethyl ester (CAPE) on Paraoxonase (PON1) activity, and levels of lipid profile, total sialic acid (TSA), total antioxidant capacity (TAC) and total oxidant capacity (TOC) in the plasma and brain tissue of mice with chlorpyrifos-ethyl (CPF)-induced Parkinson.

MATERIAL AND METHOD

In the study, 35 male Swiss albino mice were divided into 5 groups including equal number of mice as follows; intraperitoneal injection of saline for mice in control (C) group, subcutaneous injection of 80mg/kg CPF for CPF group, intraperitoneal injection of 10μmol/kg CAPE for CAPE group, subcutaneous injection of 80mg/kg CPF and intraperitoneal injection of 10μmol/kg CAPE for CPF+CAPE group and intraperitoneal injection of 10% ethanol diluted in physiological saline solution for 21days for ethanol (E) group. All the mice were fed with normal feed and tap water ad libitum. At the end of the study, PON1 activity, lipid profile (except for brain), and TSA, TAC and TOC levels in the plasma and brain tissue were analyzed. Tissue samples of brain substantia nigra were evaluated histopathologically.

RESULTS

Levels of plasma TAC, high density lipoprotein (HDL) and PON1 activity were statistically lower in CPF group than the other groups (P<0.001). Also, levels of plasma TOC, TSA, total cholesterol, triglycerides, low density lipoprotein (LDL) and very low density lipoprotein (VLDL) were statistically higher in CPF group than the other groups(P<0.001). PON1 activity and level of TAC were significantly lower in brain tissue of CPF groups (P<0.001). In addition, TOC and TSA levels were significantly higher in brain tissue in CPF group (P<0.001).

CONCLUSION

In conclusion, CAPE showed a protective effect on PON1 activity and levels of lipid profile, TSA, TAC and TOC in plasma and brain tissue and prevented the neurodegenerations in brain tissue in CPF-induced Parkinson's disease.

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.

A Case of Malathion Poisoning with Prolonged Cholinergic Toxicity

A case of severe organophosphate poisoning in a woman who ingested malathion is presented. Pralidoxime was given for more than two weeks but the lady had a poor response and developed recurrent episodes of cholinergic symptoms. Further studies are required to validate the World Health Organization regimen of pralidoxime in organophosphate poisoning.

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.

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.

Neurosteroids for the potential protection of humans against organophosphate toxicity

This article describes the therapeutic potential of neurosteroids as anticonvulsant antidotes for chemical intoxication caused by organophosphate pesticides and nerve agents or gases like sarin and soman. Toxic manifestations following nerve agent exposure, as evident in chemical attacks in Japan and Syria, include hypersecretion, respiratory distress, tremors, convulsions leading to status epilepticus (SE), and death. Benzodiazepines, such as diazepam, are the current anticonvulsants of choice for controlling nerve agent-induced life-threatening seizures, SE, and brain injury. Benzodiazepines can control acute seizures when given early, but they are less effective for delayed treatment of SE, which is characterized by rapid desensitization of synaptic GABA_A receptors, benzodiazepine resistance, and brain injury. Neurosteroid-sensitive extrasynaptic GABA_A receptors, however, remain unaffected by such events. Thus, anticonvulsant neurosteroids may produce more effective protection than benzodiazepines against a broad spectrum of chemical agents, even when given late after nerve agent exposure.

The Assessment, Evaluation, and Management of the Critically Ill Child in Resource-Limited International Settings

Providing evidence-based care to the critically ill child including assessment, evaluation, and management in resource-limited settings provides unique challenges and limitless opportunities to significantly impact morbidity and mortality in these settings. Difficulties encountered include: determining which disease processes will benefit most from critical care in resource-limited settings, lack of triage tools and adjuncts to help with assessment, finite laboratory and radiological tests, limited understanding of key findings in critically ill/injured pediatric patients, (especially by those without pediatric focused training), and finally, lack of supplies, medicines, equipment, and training of health care providers to appropriately treat critically ill children in these resource-limited settings. In this review, the most common problems encountered and possible solutions to overcome these obstacles are discussed.

Oximes in organophosphate poisoning: 60 years of hope and despair

The high number of annual fatalities following suicidal poisoning by organophosphorus (OP) pesticides and the recent homicidal use of the chemical warfare nerve agent sarin against civilian population in Syria underlines the continuous threat by these highly toxic agents. The need for an effective treatment of OP poisoning resulted in the implementation of a combination therapy with the muscarinic receptor antagonist atropine and an oxime for the reactivation of OP-inhibited acetylcholinesterase (AChE). Since the invention of the first clinically used oxime pralidoxime (2-PAM) in the 1950s ongoing research attempted to identify more effective oximes. In fact, several thousand oximes were synthesized in the past six decades. These include charged and non-charged compounds, mono- and bispyridinium oximes, asymmetric oximes, oximes with different substitutes and more recently non-oxime reactivators. Multiple in vitro and in vivo studies investigated the potential of oximes to reactivate OP-inhibited AChE and to reverse OP-induced cholinergic signs. Depending on the experimental model, the investigated species and the tested OP largely variable results were obtained by different laboratories. These findings and the inconsistent effectiveness of oximes in the treatment of OP-pesticide poisoned patients led to a continuous discussion on the value of oximes. In order to provide a forward-looking evaluation of the significance of oximes in OP poisoning multiple aspects, including intrinsic toxicity, in vitro reactivation potency, efficacy and pharmacokinetics, as well as the impact of the causative OP have to be considered. The different influencing factors in order to define the benefit and limitations of oximes in OP poisoning will be discussed.

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.

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.

Prognostic significance of estimation of pseudocholinesterase activity and role of pralidoxime therapy in organophosphorous poisoning

Background:

Organophosphorous (OP) poisoning is one of the most common poisonings seen in India. OP compounds act through inhibition of enzyme acetylcholinesterase and estimation of pseudocholinesterase (PCE) activity strengthens the diagnosis in clinically uncertain cases of OP poisoning. The role of pralidoxime (PAM) therapy in OP poisoning has been controversial.

Study Objectives:

This study was aimed to determine the prognostic significance of estimation of PCE activity and also to assess the role of PAM therapy in OP poisoning.

Materials and Methods:

Patients of suspected OP poisoning of age >12 years admitted to emergency unit at a tertiary healthcare center of north India were enrolled. Patients were categorized into two groups; group A who were given intravenous atropine and group B who were given injectable PAM along with atropine. Serum PCE level was estimated at the time of admission in all patients and severity of OP poisoning was assessed according to PCE level. Requirement of atropine, oxygen inhalation, intubation and ventilatory support, total hospital stay, and mortality were compared between different classes of severity and also between Groups A and B.

Results:

This study included a total of 70 subjects, 35 in each group with mean age of 24.99 ± 8.7 years. Out of 70 subjects 49 (70%) were male and 21 (30%) were female. Forty nine patients (70%) of OP poisoning were with suicidal intent while 21 (30%) cases were accidentally poisoned. In all suicidal cases route of poisoning was ingestion whereas in all the accidental cases route of exposure was inhalational. PCE levels were reduced in all the cases and the mean level was 3,154.16 ± 2,562.40 IU/L. The total dose of atropine required, need for oxygen inhalation and need for intubation and ventilatory support, mean duration of hospital stay and mortality rate (P = 0.003) were higher in moderate to severe cases and did not have significant difference between Groups A and B.

Conclusion:

The study recommends estimation of PCE level at admission to classify severity of OP poisoning and to estimate prognosis. This study did not find any beneficial role of PAM therapy in reducing morbidity as well as mortality.

Interaction of cholinesterase modulators with DNA and their cytotoxic activity

This research was focused on a study of the binding properties of a series of cholinesterase reactivators compounds K075 (1), K027 (2) and inhibitors compounds K524, K009 and 7-MEOTA (3-5) with calf thymus DNA. The nature of the interactions between compounds 1-5 and DNA were studied using spectroscopic techniques (UV-vis, fluorescence spectroscopy and circular dichroism). The binding constants for complexes of cholinesterase modulators with DNA were determined from UV-vis spectroscopic titrations (K=0.5 × 10(4)-8.9 × 10(5)M(-1)). The ability of the prepared analogues to relax topoisomerase I was studied with electrophoretic techniques and it was proved that ligands 4 and 5 inhibited this enzyme at a concentration of 30 μM. The biological activity of the novel compounds was assessed through an examination of changes in cell cycle distribution, mitochondrial membrane potential and cellular viability. Inhibitors 3-5 exhibited a cytotoxic effect on HL-60 (human acute promyelocytic leukaemia) cell culture, demonstrated a tendency to affect mitochondrial physiology and viability, and also forced cells to accumulate in the G1/G0-phase of the cell cycle. The cholinesterase reactivators 1 and 2 were found relatively save from the point of view of DNA binding, whereas cholinesterase inhibitors 3-5 resulted as strong DNA binding agents that limit their plausible use.

Novel cholinesterase modulators and their ability to interact with DNA

In the present work, an interaction of four cholinesterase modulators (1-4) with calf thymus DNA was studied via spectroscopic techniques (UV-Vis, fluorescent spectroscopy and circular dichroism). From UV-Vis spectroscopic analysis, the binding constants for DNA-pyridinium oximes complexes were calculated (K=3.5×10(4) to 1.4×10(5)M(-1)). All these measurements indicated that the compounds behave as effective DNA-interacting agents. Electrophoretic techniques proved that ligand 2 inhibited topoisomerase I at a concentration 5μM.

Applied clinical pharmacology and public health in rural Asia--preventing deaths from organophosphorus pesticide and yellow oleander poisoning

Self-poisoning with pesticides or plants is a major clinical problem in rural Asia, killing several hundred thousand people every year. Over the last 17 years, our clinical toxicology and pharmacology group has carried out clinical studies in the North Central Province of Sri Lanka to improve treatment and reduce deaths. Studies have looked at the effectiveness of anti-digoxin Fab in cardiac glycoside plant poisoning, multiple dose activated charcoal in all poisoning, and pralidoxime in moderate toxicity organophosphorus insecticide poisoning. More recently, using a Haddon matrix as a guide, we have started conducting public health and animal studies to find strategies that may work outside of the hospital. Based on the 2009 GSK Research in Clinical Pharmacology prize lecture, this review shows the evolution of the group's research from a clinical pharmacology approach to one that studies possible interventions at multiple levels, including the patient, the community and government legislation.

A prospective observational study on different poisoning cases and their outcomes in a tertiary care hospital

Objectives:

Poisonings and snake bites constitute major health-care problems worldwide. This observational study was conducted to identify factors associated with outcomes in such cases and to suggest strategies to improve them.

Methods:

This is a prospective study conducted in the emergency medicine department of a tertiary care hospital. The study included 102 poisoning and 64 snake bite cases. Data regarding demographics, mode of poisoning, lag time in treatment, first aid, outside and indoor treatment, co-morbid illness, duration of hospitalisation and final outcome were collected in a prestructured proforma.

Results:

The age of the patients ranged from 11 to 68 years and incidence was more common among males (69.9%) compared to females (30.1%). The major types of poisonings included organophosphorus compounds (16.3%), aluminium phosphide (12%), drug overdose (10.8%) and corrosives (6%). There were 18 (18.6%) and 1 (1.6%) deaths in poisoning and snake bite cases, respectively. In poisoning cases, the duration of hospitalisation was significantly decreased if patient received outside treatment (p = 0.02) and if he or she had lesser lag time in reaching the hospital (p = 0.009).

Conclusions:

Measures to reduce lag time and provide immediate treatment at initial encounter may be effective in reducing duration of hospitalisation and possibly mortality in poisoning and snake bite cases.

Organophosphate Exposure with Pseudocholinesterase Deficiency

A 36-year-old correctional officer was exposed to lice while at work and self-treated with chlorpyrifos, an organophosphate. The correctional officer applied chlorpyrifos to her entire body and did not wash it off for 8 to 12 hours. Eight hours after the initial application, the correctional officer developed abdominal cramps, diarrhea, sweating, excessive salivation, frequent urination, and increased bronchial secretions. After a phone consultation with the occupational health clinic, the correctional officer reported to the emergency department, was diagnosed with organophosphate toxicity, and was treated with atropine. Later testing revealed that the correctional officer had pseudocholinesterase deficiency.

Repeated pulse intramuscular injection of pralidoxime chloride in severe acute organophosphorus pesticide poisoning

OBJECTIVE

This study aimed to clarify the efficacy of 2 therapies for patients with severe acute organophosphorus pesticide poisoning, including atropine adverse effects, the length of intensive care unit (ICU) stay, complications, and mortality.

METHODS

A retrospective cohort study of 152 cases collected from May 2008 to November 2012 at 2 urban university hospitals was conducted. Patients admitted to the hospital for organophosphate poisoning were divided into 2 groups with different therapeutic regimens: group A was administered a repeated pulse intramuscular injection of pralidoxime chloride, and group B received the same initial dosage of atropine and pralidoxime chloride, but pralidoxime chloride intravenous therapy was administered for only 3 days, regardless of the length of atropine therapy. Subsequently, atropine adverse effects, length of ICU stay, complications, and mortality were statistically analyzed and compared between the 2 groups.

RESULTS

The total dose of atropine was 57.40 ± 15.14 mg in group A and 308.26 ± 139.16 mg in group B; group A received less atropine than did group B (P = .001). The length of ICU stay in group A was reduced (P = .025), and group A had fewer atropine adverse effects (P = .002). However, there was no significant difference in the mortality or complication rate between the 2 groups (P > .05).

CONCLUSION

In patients with severe poisoning, group A used less atropine, had fewer atropine adverse effects, and had a shorter ICU stay. We suggest that therapy should be started as early as possible using a sufficient amount of pralidoxime chloride started intramuscularly in combination with atropine and that the drugs should not be prematurely discontinued.

Chlorpyrifos is associated with slower serum cholinesterase recovery in acute organophosphate-poisoned patients

PURPOSE

Organophosphate poisoning (OPP) accounts for 200,000 deaths annually in developing countries. Serum cholinesterase (SChE) is of diagnostic value in patients with OPP and is checked repeatedly during the course of treatment. This study aimed to investigate the recovery pattern in patients with OPP using linear mixed models.

METHODS

Using a retrospective cohort study design, we included 212 adult OPP patients who had visited the emergency department (ED) in a tertiary medical center between 2000 and 2010. One hundred and thirty-one patients were available for analysis, as 81 patients did not meet the criteria and were excluded. Information regarding basic personal characteristics, initial vital signs and severity scores, laboratory data, type and amount of organophosphate ingested, treatment, and serial SChE values was collected. A random coefficient model with a random intercept and a random slope of time were added to address the dynamic relationships of SChE with time and other associated factors.

RESULTS

The initial SChE activity and recovery rates varied among patients with OPP. The type of organophosphate, the first SChE activity, and the initial APACHE II score were significantly related to the SChE recovery trend. Chlorpyrifos and methamidophos had significantly slower and faster SChE recovery rates, respectively, than other organophosphates. Sex, dose of Pralidoxim (2-PAM), and delay in obtaining medical assistance did not significantly affect SChE recovery.

CONCLUSIONS

This study demonstrated the pattern and associated correlates of SChE activity recovery in patients with acute OPP. Chlorpyrifos appeared to have a slower SChE activity recovery rate than other organophosphates.

New K-Oximes (K-27 and K-48) in Comparison with Obidoxime (LuH-6), HI-6, Trimedoxime (TMB-4), and Pralidoxime (2-PAM): Survival in Rats Exposed IP to the Organophosphate Paraoxon

ABSTRACT Oximes are cholinesterase reactivators used in organophosphorus compound poisoning. The purpose of the study was to compare the protective effect of the K-oximes (K-27 and K-48) in male rats with that of obidoxime (LuH-6), trimedoxime (TMB-4), and HI-6, using paraoxon (POX) as a cholinesterase inhibitor. Pralidoxime (2-PAM) was also retested. Seven groups of six rats each were used. Group 1 (G(1)) received 1 mumol/rat POX ( approximately LD(75)), the other groups (G(2-7)) received 1 mumol/rat POX + one of the six reactivators. The animals were monitored for 48 h and time of mortality was recorded. The procedure was repeated seven times. Subsequently, experiments as described were repeated using 10 and 15 mumol/rat POX. Mortality data were compared and hazards ratios (relative risks) ranked with the Cox proportional hazards model using the POX dose and group (reactivator) as time-independent covariables. K-27 followed by K-48 were the most potent reactivators. K-27 was statistically significantly superior to all other reactivators except K-48. The relative risk of death estimated by Cox analysis in K-27- and K-48-treated animals when compared with untreated animals, adjusted for the POX dose, was 0.22 (95% confidence interval [CI], 0.15 to 0.31) and 0.26 (95% CI, 0.18 to 0.37), respectively. We concluded that in the animal model used K-27 and K-48 are superior to older oximes in their ability to protect from paraoxon effects. They should be tested further using methyl- and propyl-organophosphates as toxic agents.

Toxicology in the ICU: Part 2: specific toxins

This is the second of a three-part series that reviews the generalized care of poisoned patients in the ICU. This article focuses on specific agents grouped into categories, including analgesics, anticoagulants, cardiovascular drugs, dissociative agents, carbon monoxide, cyanide, methemoglobinemia, cholinergic agents, psychoactive medications, sedative-hypnotics, amphetamine-like drugs, toxic alcohols, and withdrawal states. The first article discussed the general approach to the toxicology patient, including laboratory testing; the third article will cover natural toxins.

Pralidoxime inhibits paraoxon-induced depression of rocuronium-neuromuscular block in a time-dependent fashion

OBJECTIVE

The composite effects of organophosphorus (OP)-cholinesterase (ChE) inhibitors and oximes on the actions of nondepolarizing neuromuscular blockers in acute OP-ChE inhibitor intoxication have not been evaluated in detail. We investigated the effects of paraoxon (Pox) (an OP-ChE inhibitor) and pralidoxime (PAM) (an oxime) on the nondepolarizing neuromuscular blocking action of rocuronium.

METHODS

Isometric twitch tensions of rat left phrenic nerve-hemidiaphragm preparations elicited by indirect (phrenic nerve) supramaximal stimulation at 0.1 Hz were evaluated. Analysis of variance with post hoc testing was used for statistical comparison, and P < .05 was accepted as significant.

RESULTS

Rocuronium reduced the indirectly elicited twitch tensions in normal (50% inhibitory concentration [IC(50)], 9.84 [9.64-10.04] μM, mean [95% confidence interval]) and all pretreated diaphragms (P < .01, n = 6) in a concentration-dependent fashion. Paraoxon caused a rightward shift in the rocuronium concentration-twitch tension curve (IC(50), 15.48 [15.24-15.72] μM). The rightward shift was completely inhibited by previous copretreatment (IC(50), 9.98 [9.77-10.20] μM) and partially inhibited by simultaneous copretreatment (IC(50), 11.68 [11.45-11.91] μM) with PAM but was not inhibited by subsequent copretreatment (IC(50), 13.69 [13.39-13.99] μM) with PAM (P < .01, n = 6). Atropine did not influence the rightward shift (P < .01, n = 6).

DISCUSSION

Paraoxon depressed rocuronium-induced neuromuscular block by inhibiting ChEs, and the action of Pox was inhibited by PAM. Pralidoxime acts more intensely when applied earlier. The time-dependent effect of PAM indicates that the preceding presence of PAM in proximity to ChEs before Pox is necessary for definite suppression of the Pox-induced ChE inhibition.

Does modulation of organic cation transporters improve pralidoxime activity in an animal model of organophosphate poisoning?

OBJECTIVES

Pralidoxime is an organic cation used as an antidote in addition to atropine to treat organophosphate poisoning. Pralidoxime is rapidly eliminated by the renal route and thus has limited action. The objectives of this work were as follows. 1) Study the role of organic cation transporters in the renal secretion of pralidoxime using organic cation transporter substrates (tetraethylammonium) and knockout mice (Oct1/2⁻/⁻; Oct3⁻/⁻). 2) Assess whether sustained high plasma concentrations increase pralidoxime antidotal activity toward paraoxon-induced respiratory toxicity.

SETTING

INSERM U705, Faculté de Pharmacie, Université Paris Descartes, 4 Avenue de l'Observatoire, 75006 Paris, France.

SUBJECTS

Rodents: Knockout mice (Oct1/2⁻/⁻; Oct3⁻/⁻) and Sprague-Dawley rats.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In rats, the renal clearance of pralidoxime was 3.6-fold higher than the creatinine clearance. Pretreatment with tetraethylammonium (75 mg/kg) in rats or deficiencies in organic cation transporters 1 and 2 in mice (Oct1/2⁻/⁻) resulted in a significant increase in plasma pralidoxime concentrations. Lack of Oct3 did not alter plasma pralidoxime concentrations. The antidotal activity of pralidoxime (50 mg/kg intramuscularly) was longer and with greater effect, resulting in a return to normal values when administered to rats pretreated with tetraethylammonium.

CONCLUSIONS

Pralidoxime is secreted in rats and mice by renal Oct1 and/or Oct2 but not by Oct3. Modulation of organic cation transporter activity increased the plasma pralidoxime concentrations and the antidotal effect of pralidoxime with sustained return within the normal range of respiratory variables in paraoxon-poisoned rats. These results suggest a promising approach in an animal model toward the increase in efficiency of pralidoxime. However, further studies are needed before these results are extended to human poisoning.