Comparative Analysis of Outcomes in Acute Organophosphate Poisoning With and Without N-acetyl Cysteine Intervention

INTRODUCTION

Organophosphorus poisoning (OPP) stands as a significant health concern in numerous regions, especially in developing nations. Despite the rising complexities and case fatalities associated with exposure, the treatment approach has remained unchanged for many years. Based on clinical insights, certain pharmacologic agents have demonstrated utility in enhancing outcomes and reducing complications arising from this type of exposure.

OBJECTIVES

The objective of this study is to compare the outcome of N-acetyl cysteine in the treatment of acute organophosphate poisoning cases. In terms of a) its impact on the requirement of atropine, b) Length of hospital stay, and mortality.

METHODS

The study was conducted in the intensive care unit (ICU) of the General Hospital Lahore. Thirty patients with a history and clinical presentation indicative of acute organophosphorus poisoning were randomly divided into two groups in a 1:1 ratio. The treatment group received parenteral administration of atropine, pralidoxime, and N-acetylcysteine (NAC) as an adjuvant, and the control group received standard treatment for acute organophosphate (OP) toxicity.

RESULT

Throughout the study duration, 30 patients suffering acute organophosphate (OP) toxicity (14 men, 16 women) were examined, with an age mean of (25.83±11.59) years. In the interventional group, only four patients required ICU admission, but in the control group, eight patients were admitted to ICU. The correlation result between the dose of atropine and length of hospital stays was not statistically significant between both study groups (<0.005). Plasma Cholinesterase (PChE) level (KU L-1) and total dose of Pralidoxime (g) were statistically significant in the length of hospital stay. The data was not normally distributed, so the non-parametric tests were applied. The Wilcoxon ranked test showed significant improvement in both the controlled and interventional groups because the p-value was (<0.005). Intergroup comparison analyzed by using the Mann-Whitney U test showed a significant reduction in the severity and other associated symptoms in the interventional group because the p-value was (0.001).

CONCLUSION

The outcome demonstrated that the NAC group had a decreased demand for atropine rather than Pralidoxime. In the NAC group, the length of hospital stay and mortality was decreased. The administration of NAC to the present study procedure for acute organophosphate (OP) poisoning is suggested.

CON: Oximes should be used routinely in organophosphorus insecticide poisoning

Organophosphorus (OP) insecticide poisoning causes respiratory failure due to acetylcholinesterase (AChE) inhibition. The AChE reactivating antidote pralidoxime was developed in the 1950s and soon noted to benefit patients occupationally poisoned with the highly potent OP insecticide parathion. Routine use of pralidoxime and other oximes such as obidoxime then became widely recommended. However, nearly all severe cases of OP poisoning now result from self-poisoning with large volumes of less potent (WHO hazard class Ib and II) insecticides and co-formulated solvents. Unfortunately, oxime clinical trials have never shown benefit from their use for these patients, and some have shown that pralidoxime may be associated with harm, including increased mortality. Oximes should not be used routinely for the care of OP insecticide poisoned patients until translational and clinical studies have identified a safe and effective oxime regimen and identified the patients who benefit.

FDA-Approved Oximes and Their Significance in Medicinal Chemistry

Despite the scientific advancements, organophosphate (OP) poisoning continues to be a major threat to humans, accounting for nearly one million poisoning cases every year leading to at least 20,000 deaths worldwide. Oximes represent the most important class in medicinal chemistry, renowned for their widespread applications as OP antidotes, drugs and intermediates for the synthesis of several pharmacological derivatives. Common oxime based reactivators or nerve antidotes include pralidoxime, obidoxime, HI-6, trimedoxime and methoxime, among which pralidoxime is the only FDA-approved drug. Cephalosporins are β-lactam based antibiotics and serve as widely acclaimed tools in fighting bacterial infections. Oxime based cephalosporins have emerged as an important class of drugs with improved efficacy and a broad spectrum of anti-microbial activity against Gram-positive and Gram-negative pathogens. Among the several oxime based derivatives, cefuroxime, ceftizoxime, cefpodoxime and cefmenoxime are the FDA approved oxime-based antibiotics. Given the pharmacological significance of oximes, in the present paper, we put together all the FDA-approved oximes and discuss their mechanism of action, pharmacokinetics and synthesis.

Experimental and Established Oximes as Pretreatment before Acute Exposure to Azinphos-Methyl

Poisoning with organophosphorus compounds (OPCs) represents an ongoing threat to civilians and rescue personal. We have previously shown that oximes, when administered prophylactically before exposure to the OPC paraoxon, are able to protect from its toxic effects. In the present study, we have assessed to what degree experimental (K-27; K-48; K-53; K-74; K-75) or established oximes (pralidoxime, obidoxime), when given as pretreatment at an equitoxic dosage of 25% of LD01, are able to reduce mortality induced by the OPC azinphos-methyl. Their efficacy was compared with that of pyridostigmine, the only FDA-approved substance for such prophylaxis. Efficacy was quantified in rats by Cox analysis, calculating the relative risk of death (RR), with RR=1 for the reference group given only azinphos-methyl, but no prophylaxis. All tested compounds significantly (p ≤ 0.05) reduced azinphos-methyl-induced mortality. In addition, the efficacy of all tested experimental and established oximes except K-53 was significantly superior to the FDA-approved compound pyridostigmine. Best protection was observed for the oximes K-48 (RR = 0.20), K-27 (RR = 0.23), and obidoxime (RR = 0.21), which were significantly more efficacious than pralidoxime and pyridostigmine. The second-best group of prophylactic compounds consisted of K-74 (RR = 0.26), K-75 (RR = 0.35) and pralidoxime (RR = 0.37), which were significantly more efficacious than pyridostigmine. Pretreatment with K-53 (RR = 0.37) and pyridostigmine (RR = 0.52) was the least efficacious. Our present data, together with previous results on other OPCs, indicate that the experimental oximes K-27 and K-48 are very promising pretreatment compounds. When penetration into the brain is undesirable, obidoxime is the most efficacious prophylactic agent already approved for clinical use.

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.

Organophosphorus nerve agent poisoning: managing the poisoned patient

Organophosphorus (OP) nerve agent poisoning made the headlines in 2018 with the nerve agent 'Novichok' poisonings in Salisbury, England. This event highlighted a gap in the knowledge of most clinicians in the UK. In response, this special article aims to enlighten and signpost anaesthetists and intensivists towards the general management of OP nerve agent poisoned patients. Drawing on a broad range of sources, we will discuss what OP nerve agents are, how they work, and how to recognise and treat OP nerve agent poisoning. OP nerve agents primarily act by inhibiting the enzyme acetylcholinesterase, causing an acute cholinergic crisis; death usually occurs through respiratory failure. The antimuscarinic agent atropine, oximes (to reactivate acetylcholinesterase), neuroprotective drugs, and critical care remain the mainstays of treatment. The risk to medical staff from OP poisoned patients appears low, especially if there is a thorough decontamination of the poisoned patient and staff wear appropriate personal protective equipment. The events in Salisbury in the past year were shocking, and the staff at Salisbury District General Hospital performed admirably in treating those affected by Novichok nerve agent poisoning. We eagerly anticipate their future clinical publications so that the medical community might learn from their valuable experiences.

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.

High Dose of Pralidoxime Reverses Paraoxon-Induced Respiratory Toxicity in Mice

Objective

The efficiency of pralidoxime in the treatment of human organophosphates poisoning is still unclear. In a rat model, we showed that pralidoxime induced a complete but concentration-dependent reversal of paraoxon-induced respiratory toxicity. The aim of this study was to assess the efficiency of pralidoxime in a species other than rats.

Methods

A dose of diethylparaoxon corresponding to 50% of the median lethal dose was administered subcutaneously to male F1B6D2 mice. Ascending single pralidoxime doses of 10, 50-100 and 150 mg kg^-1 were administered intramuscularly 30 min after diethylparaoxon administration. Ventilation at rest was assessed using whole-body plethysmography and mice temperature was assessed using infrared telemetry. Results are expressed as mean±SE. Statistical analysis used non-parametric tests.

Results

From 30 to 150 min post-injection, diethylparaoxon induced clinical symptoms and a decrease in respiratory frequency, which resulted from an increase in expiratory and inspiratory times associated with an increase in the tidal volume. In the 10-, 50- and 100-mg kg^-1 pralidoxime groups, there was a trend towards a non-significant improvement of paraoxon-induced respiratory toxicity. The 150 mg kg^-1 dose of pralidoxime induced a significant reversal of all respiratory parameters.

Conclusion

In the present study, a toxic but non-lethal model of diethylparaoxon in awake, unrestrained mice was observed. By administering an equipotent dose of diethylparaoxon to rats, a 150 mg kg^-1 dose of pralidoxime administered alone completely reversed diethylparaoxon-induced respiratory toxicity in mice. The dose dependency of reversal suggests that further studies are needed for assessing plasma concentrations of pralidoxime resulting in reversal of toxicity.

Nanometric MIL-125-NH₂ Metal-Organic Framework as a Potential Nerve Agent Antidote Carrier

The three-dimensional (3D) microporous titanium aminoterephthalate MIL-125-NH₂ (MIL: Material of Institut Lavoisier) was successfully isolated as monodispersed nanoparticles, which are compatible with intravenous administration, by using a simple, safe and low-cost synthetic approach (100 °C/32 h under atmospheric pressure) so that for the first time it could be considered for encapsulation and the release of drugs. The nerve agent antidote 2-[(hydroxyimino)methyl]-1-methyl-pyridinium chloride (2-PAM or pralidoxime) was effectively encapsulated into the pores of MIL-125-NH₂ as a result of the interactions between 2-PAM and the pore walls being mediated by π-stacking and hydrogen bonds, as deduced from infrared spectroscopy and Monte Carlo simulation studies. Finally, colloidal solutions of MIL-125-NH₂ nanoparticles exhibited remarkable stability in different organic media, aqueous solutions at different pH and under relevant physiological conditions over time (24 h). 2-PAM was rapidly released from the pores of MIL-125-NH₂ in vitro.

In silico and in vitro evaluation of two novel oximes (K378 and K727) in comparison to K-27 and pralidoxime against paraoxon-ethyl intoxication

Organophosphate (OP) poisoning is a major global health issue; while compounds from this group have been used intensively over the last century, an effective antidote is still lacking. Oxime-type acetylcholinesterase (AChE) reactivators are used to reactivate the OP inhibited AChE. Pralidoxime is the only US Food and Drug Administration approved oxime for therapeutic use but its efficacy has been disappointing. Two novel oximes (K378 and K727) were investigated in silico and in vitro and compared with an experimental oxime (kamiloxime; K-27) and pralidoxime. In silico the molecular interactions between AChE and oximes were examined and binding energies were assessed. LogP (predicted log of the octanol/water partition coefficient) was estimated. In vitro the intrinsic ability of the oximes to inhibit AChE (IC₅₀) and their reactivation potency (R₅₀) when used in paraoxon inhibited human RBC-AChE was determined. Molecular docking revealed that K378 and K727 bind to the peripheral site(s) with high binding energies in contrast to the central binding of K-27 and pralidoxime. LogP values indicating that the novel compounds are significantly less hydrophilic than K-27 or pralidoxime. IC₅₀ of K378 and K727 were comparable (0.9 and 1 µM, respectively) but orders of magnitude lower than comparators. R₅₀ values revealed their inability to reactivate paraoxon inhibited AChE. It is concluded that the novel oximes K378 and K727 are unlikely to be clinically useful. The in silico and in vitro studies described allow avoidance of unnecessary in vivo animal work and contribute to the reduction of laboratory animal use.

Protective effects of the antihistamine promethazine aginst acute paraxon-methyl and dicrotophos toxicity in adult rats

Organophosphorus compound poisoning (OPC) is a global issue. The problem is aggravated with the threats of terrorist use, unintentional use and irresponsible practice as happened recently in turmoil countries. The purpose of the current study was to investigate the old-generation antihistamine promethazine (PROM), a drug with multi pharmacological actions, as an antidote to extremely and highly toxic (WHO's class IA and IB) OPC poisoning in experimental animal models conducted on adult male wistar rats. Experimental groups were treated intraperitoneal (i.p.) with LD70 of methyl paraoxon (MPOX), class IA and dicrotophos (DCP), class IB alone and a combination of simultaneously i.p. injection of PROM. Mortality was recorded at 30 minutes, 1, 2, 3, 4, 24, 48 hours post injections. RBC-AChE was measured in survivals. MPOX was chosen for further studies with atropine (ATR) and pralidoxime (PAM). In addition to Kaplan-Meir survival analysis, serum lactate dehydrogenase (LDH) and creatinine kinase (CK) from serum were measured in all experimental groups with MPOX. The results revealed significant protection by PROM in both MPOX and DCP intoxicated rats, though the inhibition of RBC-AChE was high. The observed results show that groups treated with a combination of MPOX and PROM or MPOX, PROM, and PAM were protected higher than those treated with MPOX and ATR or MPOX, ATR, and PAM though statistically not significantly different (P ≤ 0.05). No effect was observed on the activity of LDH and CK. The study concludes that PROM may be effectively used in OPC poisoning. However, risk/benefits trials and further studies with different doses and other OPC groups are warranted.

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.

Mini review on blood-brain barrier penetration of pyridinium aldoximes

This paper reviews the blood-brain barrier (BBB) penetration of newly developed pyridinium aldoximes. Pyridinium aldoximes are highly charged hydrophilic compounds used in the treatment of subjects exposed to organophosphonates because they are effective as acetylcholinesterase reactivators. Pyridinium aldoximes have antidotal effects against poisoning with cholinesterase inhibitors, a frequent problem affecting people working with organophosphate-based insecticides and pesticides. Toxic organophosphonate products such as sarin and tabun can be used by terrorists as chemical warfare agents. This poses a severe challenge to all innocent and peace-loving people worldwide. This review gives a brief summary of BBB transporters and description of the current in vitro and in vivo methods for the characterization of BBB penetration of established and novel pyridinium aldoximes. The authors provide a putative mechanism of penetration, outline some future ways of formulation and discuss the possible advantages and disadvantages of increasing BBB penetration.

Survival pattern in patients with acute organophosphate poisoning on mechanical ventilation: A retrospective intensive care unit-based study in a tertiary care teaching hospital

BACKGROUND AND AIMS

Organophosphorus (OP) compound poisoning is one of the most common poisonings in India. The aim of the study was to study the outcomes and predictors of mortality in patients with acute OP poisoning requiring mechanical ventilation.

METHODS

A retrospective study was conducted in the intensive care unit and 117 patients were included. Diagnosis was performed from the history taken either from the patient or from the patient's relatives. Demographic data, month of the year, mode of poisoning, common age group, duration of mechanical ventilation, time of starting pralidoxime (PAM), and mortality were recorded. Chi square test, Pearson correlation test, and multivariate binary logistic regression analysis was used. Data are presented as mean ± SD.

RESULTS

91.86% (79/86) of cases were suicidal and remaining cases were accidental. Duration of mechanical ventilation varied from less than 48 hours to more than 7 days. Mortality rate was 33.3%, 7.2%, and 100% in those who required mechanical ventilation for more than 7 days, 5 to 7 days, and 2 to 4 days, respectively. Lag time was less than 6 hrs in 13 patients and all of them survived. 17.1% and 28.1% patients died in whom PAM was started 6 to 12 hrs and 13 to 24 hrs after poisoning, respectively. There was statistically significant positive correlation between lag time of starting of PAM with duration of mechanical ventilation and total dose of PAM (P < 0.0001). None of the predictors age, lag time, severity of poisoning, and duration of ventilation were independent predictors of death. Overall mortality rate was 18.6%.

CONCLUSION

Mortality from OP compound poisoning is directly proportionate to the severity of poisoning, delay in starting PAM, and duration of mechanical ventilation. Death is not dependent on a single factor, rather contributory to these factors working simultaneously.

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.

Reactivation of plasma butyrylcholinesterase by pralidoxime chloride in patients poisoned by WHO class II toxicity organophosphorus insecticides

Some clinicians assess the efficacy of pralidoxime in organophosphorus (OP) poisoned patients by measuring reactivation of butyrylcholinesterase (BuChE). However, the degree of BuChE inhibition varies by OP insecticide, and it is unclear how well oximes reactivate BuChE in vivo. We aimed to assess the usefulness of BuChE activity to monitor pralidoxime treatment by studying its reactivation after pralidoxime administration to patients with laboratory-proven World Health Organization (WHO) class II OP insecticide poisoning. Patient data were derived from 2 studies, a cohort study (using a bolus treatment of 1g pralidoxime chloride) and a randomized controlled trial (RCT) (comparing 2g pralidoxime over 20min, followed by an infusion of 0.5g/h, with placebo). Two grams of pralidoxime variably reactivated BuChE in patients poisoned by 2 diethyl OP insecticides, chlorpyrifos and quinalphos; however, unlike acetylcholinesterase reactivation, this reactivation was not sustained. It did not reactivate BuChE inhibited by the dimethyl OPs dimethoate or fenthion. The 1-g dose produced no reactivation. Pralidoxime produced variable reactivation of BuChE in WHO class II OP-poisoned patients according to the pralidoxime dose administered, OP ingested, and individual patient. The use of BuChE assays for monitoring the effect of pralidoxime treatment is unlikely to be clinically useful.

Kinin-B2 receptor exerted neuroprotection after diisopropylfluorophosphate-induced neuronal damage

The kinin-B2 receptor (B2BKR) activated by its endogenous ligand bradykinin participates in various metabolic processes including the control of arterial pressure and inflammation. Recently, functions for this receptor in brain development and protection against glutamate-provoked excitotoxicity have been proposed. Here, we report neuroprotective properties for bradykinin against organophosphate poisoning using acute hippocampal slices as an in vitro model. Following slice perfusion for 10min with diisopropylfluorophosphate (DFP) to initiate the noxious stimulus, responses of pyramidal neurons upon an electric impulse were reduced to less than 30% of control amplitudes. Effects on synaptic-elicited population spikes were reverted when preparations had been exposed to bradykinin 30min after challenging with DFP. Accordingly, bradykinin-induced population spike recovery was abolished by HOE-140, a B2BKR antagonist. However, the kinin-B1 receptor (B1BKR) agonist Lys-des-Arg(9)-bradykinin, inducing the phosphorylation of mitogen-activated protein kinase (MEK/MAPK) and cell death, abolished bradykinin-mediated neuroprotection, an effect, which was reverted by the ERK inhibitor PD98059. In agreement with pivotal B1BKR functions in this process, antagonism of endogenous B1BKR activity alone was enough for restoring population spike activity. On the other hand pralidoxime, an oxime, reactivating acetylcholinesterase (AChE) after organophosphate poisoning, induced population spike recovery after DFP exposure in the presence of bradykinin and Lys-des-Arg(9)-bradykinin. Lys-des-Arg(9)-bradykinin did not revert protection exerted by pralidoxime, however when instead bradykinin and Ly-des-Arg(9)-bradykinin were superfused together, recovery of population spikes diminished. These findings again confirm the neuroprotective feature of bradykinin, which is, diminished by its endogenous metabolites, stimulating the B1BKR, providing a novel understanding of the physiological roles of these receptors.

Intensive care management of organophosphate insecticide poisoning

INTRODUCTION

Organophosphate (OP) insecticides inhibit both cholinesterase and pseudo-cholinesterase activities. The inhibition of acetylcholinesterase causes accumulation of acetylcholine at synapses, and overstimulation of neurotransmission occurs as a result of this accumulation. The mortality rate of OP poisoning is high. Early diagnosis and appropriate treatment is often life saving. Treatment of OP poisoning consists of intravenous atropine and oximes. The clinical course of OP poisoning may be quite severe and may need intensive care management. We report our experience with the intensive care management of serious OP insecticide poisonings.

METHODS

A retrospective study was performed on the patients with OP poisoning followed at our medical intensive care unit. Forty-seven patients were included. Diagnosis was performed from the history taken either from the patient or from the patient's relatives about the agent involved in the exposure. Diagnosis could not be confirmed with serum and red blood cell anticholinesterase levels because these are not performed at our institution. Intravenous atropine and pralidoxime was administered as soon as possible. Pralidoxime could not be given to 16 patients: 2 patients did not receive pralidoxime because they were late admissions and 14 did not receive pralidoxime because the Ministry of Health office was out of stock. Other measures for the treatment were gastric lavage and administration of activated charcoal via nasogastric tube, and cleansing the patient's body with soap and water. The patients were intubated and mechanically ventilated if the patients had respiratory failure, a depressed level of consciousness, which causes an inability to protect the airway, and hemodynamic instability. Mechanical ventilation was performed as synchronized intermittent mandatory ventilation + pressure support mode, either as volume or pressure control. Positive end expiratory pressure was titrated to keep SaO2 above 94% with 40% FIO2. Weaning was performed using either T-tube trials or pressure support weaning. The chi-square test was used for statistical analysis. Data are presented as mean +/- standard deviation.

RESULTS

There were 25 female and 22 male patients. Thirty-two (68%) were suicide attempts and 15 (32%) were accidental exposure. The gastrointestinal route was the main route in 44 (93.6%) patients. The mortality rates for the patients who did and did not receive pralidoxime were 32 and 18.7%, respectively, and were not statistically different. The most frequent signs were meiosis, change in mental status, hypersalivation and fasciculations. Ten patients (21.2%) required mechanical ventilation. The mortality rate for the patients who required mechanical ventilation was 50%, but the rate was 21.6% for the patients who were not mechanically ventilated. Intermediate syndrome was observed in 9 (19.1%) patients. Complications were observed in 35 (74.4%) patients. These complications were respiratory failure (14 patients), aspiration pneumonia (10 patients), urinary system infection (6 patients), convulsion (4 patients) and septic shock (1 patient). The duration of the intensive care stay was 5.2 +/- 3.0 days.

DISCUSSION

Ingestion of OP compounds for suicidal purposes is a major problem, especially in developing countries. Thirty-two (68%) of our patients used the OP insecticide for suicide. Two patients did not receive pralidoxime because of delayed admission and they were successfully treated with atropine alone. Three of the patients who did not receive pralidoxime because of unavailability died. The mortality rate was no different between the patients treated with pralidoxime or those without pralidoxime. De Silva and coworkers have also reported that the mortality rate was not different between each group. Three patients with intermediate syndrome died due to delay for endotracheal intubation. The average respiratory rate of these patients increased from 22 to 38 breaths/min, which is an important sign of respiratory distress. The nurse to patient ratio was increased after these events. Early recognition of respiratory failure resulting in intubation and mechanical ventilation is a life-saving intervention for patients with OP poisoning. Respiratory failure is the most troublesome complication, which was observed in 35 (74.4%) patients. Patients with OP poisoning may have respiratory failure for many reasons, including aspiration of the gastric content, excessive secretions, pneumonia and septicemia complicating acute respiratory distress syndrome.

CONCLUSIONS

OP insecticide poisoning is a serious condition that needs rapid diagnosis and treatment. Since respiratory failure is the major reason for mortality, careful monitoring, appropriate management and early recognition of this complication may decrease the mortality rate among these patients.