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Exogenous, well-established antioxidant N-acetylcysteine can reduce or prevent the deleterious effects of pesticides. In this study, utilizing a mouse model of daily single dose of N-acetylcysteine administration, we investigated the impact of this adjuvant on the treatment with atropine and/or obidoxime as well as oxidative stress response in pyrimiphos-methyl-induced toxicity. We found that N-acetylcysteine significantly reduces the oxidative stress generated by pyrimiphos-methyl. The therapy consisting of atropine and/or obidoxime routinely used in organophosphorous insecticide poisonings, including pyrimiphos-methyl, had no effect on the antioxidant properties of N-acetylcysteine. Adjunctive treatment offered by N-acetylcysteine fills therapeutic gap and may provide the full potential against pyrimiphos-methyl-induced toxicity., (© 2024 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society). Published by John Wiley & Sons Ltd.)

In poisoning with organophosphorus compounds (OP), patients can only profit from the regeneration of acetylcholinesterase, when the poison load has dropped below a toxic level. Every measure that allows an increase of synaptic acetylcholinesterase (AChE) activity at the earliest is essential for timely termination of the cholinergic crisis. Only drug-induced reactivation allows fast restoration of the inhibited AChE. Obidoxime and pralidoxime have proved to be able to reactivate inhibited cholinesterase thereby saving life of poisoned animals. A plasma level of obidoxime or pralidoxime allowing reactivation in humans poisoned by OP can be adjusted. There is no doubt that obidoxime and pralidoxime are able to reactivate OP-inhibited AChE activity in poisoned patients, thereby increasing AChE activity and contributing substantially to terminate cholinergic crisis. Hence, a benefit may be expected when substantial reactivation is achieved. A test system allowing determination of red blood cell AChE activity, reactivatability, inhibitory equivalents and butyrylcholinesterase activity is available for relatively low cost. If any reactivation is possible while inhibiting equivalents are present, oxime therapy should be maintained. In particular, when balancing the benefit risk assessment, obidoxime or palidoxime should be given as soon as possible and as long as a substantial reactivation may be expected., (© 2022 The Authors. British Journal of Clinical Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Nerve agent exposure is generally treated by an antidote formulation composed of a muscarinic antagonist, atropine sulfate (ATR), and a reactivator of acetylcholinesterase (AChE) such as pralidoxime, obidoxime (OBI), methoxime, trimedoxime or HI-6 and an anticonvulsant. Organophosphates (OPs) irreversibly inhibit AChE, the enzyme responsible for termination of acetylcholine signal transduction. Inhibition of AChE leads to overstimulation of the central and peripheral nervous system with convulsive seizures, respiratory distress and death as result. The present study evaluated the efficacy and pharmacokinetics (PK) of ATR/OBI following exposure to two different VX dose levels. The PK of ATR and OBI administered either as a single drug, combined treatment but separately injected, or administered as the ATR/OBI co-formulation, was determined in plasma of naïve guinea pigs and found to be similar for all formulations. Following subcutaneous VX exposure, ATR/OBI-treated animals showed significant improvement in survival rate and progression of clinical signs compared to untreated animals. Moreover, AChE activity after VX exposure in both blood and brain tissue was significantly higher in ATR/OBI-treated animals compared to vehicle-treated control. In conclusion, ATR/OBI has been proven to be efficacious against exposure to VX and there were no PK interactions between ATR and OBI when administered as a co-formulation., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Suicidal ingestion of organophosphorus (OP) or carbamate (CM) compounds challenges health care systems worldwide, particularly in Southeast Asia. The diagnosis and treatment of OP or CM poisoning is traditionally based on the clinical appearance of the typical cholinergic toxidrome, e.g. miosis, salivation and bradycardia. Yet, clinical signs might be inconclusive or even misleading. A current case report highlights the importance of enzymatic assays to provide rapid information and support clinicians in diagnosis and rational clinical decision making. Furthermore, the differentiation between OP and CM poisoning seems important, as an oxime therapy will most probably not provide benefit in CM poisoning, but-as every pharmaceutical product-it might result in adverse effects. The early identification of the causing agent and the amount taken up in the body are helpful in planning of the therapeutic regimen including experimental strategies, e.g. the use of human blood products to facilitate scavenging of the toxic agent. Furthermore, the analysis of biotransformation products and antidote levels provides additional insights into the pathophysiology of OP or CM poisoning. In conclusion, cholinesterase activities and modern analytical methods help to provide a more effective treatment and a thorough understanding of individual cases of OP or CM 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., (Published by Elsevier B.V.)

The ability of two novel bispyridinium oximes K727 and K733 and currently available oximes (HI-6, obidoxime) to reactivate sarin-inhibited acetylcholinesterase and to reduce acute toxicity of sarin was evaluated. To investigate the reactivating efficacy of the oximes, the rats were administered intramuscularly with atropine and oximes in equitoxic doses corresponding to 5% of their LD50 values at 1 min after the intramuscular administration of sarin at a dose of 24 µg/kg (LD50). The activity of acetylcholinesterase was measured at 60 min after sarin poisoning. The LD50 value of sarin in non-treated and treated mice was assessed using probit-logarithmical analysis of death occurring within 24 h after intramuscular administration of sarin at five different doses. In vivo determined percentage of reactivation of sarin-inhibited rat blood, diaphragm and brain acetylcholinesterase showed that the potency of both novel oximes K727 and K733 to reactivate sarin-inhibited acetylcholinesterase roughly corresponds to the reactivating efficacy of obidoxime. On the other hand, the oxime HI-6 was found to be the most efficient reactivator of sarin-inhibited acetylcholinesterase. While the oxime HI-6 was able to reduce the acute toxicity of sarin >3 times, both novel oximes and obidoxime decreased the acute toxicity of sarin <2 times. Based on the results, we can conclude that the reactivating and therapeutic efficacy of both novel oximes K727 and K733 is significantly lower compared to the oxime HI-6 and, therefore, they are not suitable for the replacement of the oxime HI-6 for the antidotal treatment of acute sarin poisoning.

Aim: To assess the role of butyrylcholinesterase (BuChE) activity as a predictive biomarker in acute cholinesterase inhibitor poisoning in a cohort from a regional tertiary care hospital., Material and Methods: Plasma butyrylcholinesterase activity on admission and at regular intervals during admission and clinical outcomes of cases admitted to the Toxicology Clinic of "Sf. Spiridon" Emergency Hospital Iasi, Romania between 1983 and 2013 were evaluated., Results: A total number of 606 patients were included in the study. The mean BuChE-activity level on admission was 1.54 ml NaOH N/100. A correlation between the amount of ingested organophosphates/carbamates (OPs/CMs) and low cholinesterase activity on admission was found. 66.66% of the patients were admitted to hospital within 8 hours after poisoning. The initial, daily and mean total atropine doses administrated were 9.65 mg, 10.51 mg and 69.39 mg, respectively. 67.16% of the investigated patients received Toxogonin for 6.41 days showing a slow increase in BuChE activity afterwards. The average number of hospital days was 11.22. The study revealed that complications occurred in patients with BuChE-activity levels below 1.4 mL NaOH N/100. A positive correlation between mortality rate (3.8% of patients) and the lowest BuChE-activity level on admission (0.89 mL NaOH N/100) was found., Conclusions: BuChE activity on admission and its level during hospital stay represent an important predictive factor for acute cholinesterase inhibitors poisoning.

Poisoning with organophosphates (OPs) may induce status epilepticus (SE), leading to severe brain damage. Our objectives were to investigate whether OP-induced SE leads to the emergence of spontaneous recurrent seizures (SRSs), the hallmark of chronic epilepsy, and if so, to assess the efficacy of benzodiazepine therapy following SE onset in preventing the epileptogenesis. We also explored early changes in hippocampal pyramidal cells excitability in this model. Adult rats were poisoned with the paraoxon (450μg/kg) and immediately treated with atropine (3mg/kg) and obidoxime (20mg/kg) to reduce acute mortality due to peripheral acetylcholinesterase inhibition. Electrical brain activity was assessed for two weeks during weeks 4-6 after poisoning using telemetric electrocorticographic intracranial recordings. All OP-poisoned animals developed SE, which could be suppressed by midazolam. Most (88%) rats which were not treated with midazolam developed SRSs, indicating that they have become chronically epileptic. Application of midazolam 1min following SE onset had a significant antiepileptogenic effect (only 11% of the rats became epileptic; p=0.001 compared to non-midazolam-treated rats). Applying midazolam 30min after SE onset did not significantly prevent chronic epilepsy. The electrophysiological properties of CA1 pyramidal cells, assessed electrophysiologically in hippocampal slices, were not altered by OP-induced SE. Thus we show for the first time that a single episode of OP-induced SE in rats leads to the acquisition of chronic epilepsy, and that this epileptogenic outcome can be largely prevented by immediate, but not delayed, administration of midazolam. Extrapolating these results to humans would suggest that midazolam should be provided together with atropine and an oxime in the immediate pharmacological treatment of OP poisoning., (Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.)

The neuroprotective effects of a newly developed oxime K203 and currently available oximes (obidoxime, HI-6) in combination with atropine in rats poisoned with sarin were studied. The sarin-induced neurotoxicity was monitored using a functional observatory battery at 2 hr after sarin challenge. The results indicate that the potency of a novel bispyridinium oxime K203 to counteract sarin-induced neurotoxicity is relatively low and roughly corresponds to the neuroprotective efficacy of obidoxime. Among tested oximes, the oxime HI-6 seems to be significanlty more efficacious to counteract acute neurotoxicity of sarin than commonly used obidoxime and a newly developed oxime K203. Thus, the oxime K203 does not provide any beneficial effect for the antidotal treatment of acute poisoning with sarin in comparison with the oxime HI-6 that should be considered to be the best oxime for antidotal treatment of acute sarin poisonings., (© 2012 The Authors Basic & Clinical Pharmacology & Toxicology © 2012 Nordic Pharmacological Society.)

The potency of bispyridinium acetylcholinesterase reactivator KR-22934 in reactivating tabun-inhibited acetylcholinesterase and reducing tabun-induced lethal toxic effects was compared with the oxime K203 and commonly used oximes. Studies determining percentage of reactivation of tabun-inhibited blood and tissue acetylcholinesterase in rats showed that the reactivating efficacy of KR-22934 was slightly higher than the reactivating efficacy of K203 and roughly corresponded to the reactivating efficacy of obidoxime and trimedoxime in blood and diaphragm. On the other hand, the oxime KR-22934 was not able to reactivate tabun-inhibited acetylcholinesterase in the brain. The therapeutic efficacy of all oximes studied approximately corresponded to their reactivating efficacy. Based on the results, one can conclude that the oxime KR-22934 is not suitable for the replacement of commonly used oximes for the antidotal treatment of tabun poisoning in spite of its potency to reactivate tabun-inhibited acetylcholinesterase in the peripheral compartment (blood, diaphragm).

Tabun belongs to the most toxic nerve agents. Its mechanism of action is based on acetylcholinesterase (AChE) inhibition at the peripheral and central nervous systems. Therapeutic countermeasures comprise administration of atropine with cholinesterase reactivators able to reactivate the inhibited enzyme. Reactivation of AChE is determined mostly biochemically without specification of different brain structures. Histochemical determination allows a fine search for different structures but is performed mostly without quantitative evaluation. In rats intoxicated with tabun and treated with a combination of atropine and HI-6, obidoxime, or new oxime K048, AChE activities in different brain structures were determined using biochemical and quantitative histochemical methods. Inhibition of AChE following untreated tabun intoxication was different in the various brain structures, having the highest degree in the frontal cortex and reticular formation and lowest in the basal ganglia and substantia nigra. Treatment resulted in an increase of AChE activity detected by both methods. The highest increase was observed in the frontal cortex. This reactivation was increased in the order HI-6 < K048 < obidoxime; however, this order was not uniform for all brain parts studied. A correlation between AChE activity detected by histochemical and biochemical methods was demonstrated. The results suggest that for the mechanism of action of the nerve agent tabun, reactivation in various parts of the brain is not of the same physiological importance. AChE activity in the pontomedullar area and frontal cortex seems to be the most important for the therapeutic effect of the reactivators. HI-6 was not a good reactivator for the treatment of tabun intoxication.

The ability of the newly developed bispyridinium compound K203 and its fluorinated analogue KR-22836 to reduce tabun-induced acute neurotoxic signs and symptoms was compared with the currently available reactivator of acetylcholinesterase-obidoxime. Tabun-induced neurotoxicity and the neuroprotective effects of all tested oximes in combination with atropine in rats poisoned with tabun at a sublethal dose (200 μg/kg intramuscularly (i.m.); 80% of LD(50) value) were monitored by a functional observational battery at 24 hr after tabun challenge. The results indicate that all tested oximes combined with atropine were able to survive tabun-poisoned rats 24 hr after tabun challenge while one non-treated tabun-poisoned rat died within 24 hr after tabun poisoning. All tested oximes combined with atropine were able to decrease tabun-induced neurotoxicity in the case of sublethal poisoning but they did not eliminate all tabun-induced acute neurotoxic signs and symptoms. While the ability to reduce tabun-induced acute neurotoxicity of obidoxime and K203 was similar, the neuroprotective efficacy of KR-22836 was slightly higher compared to other tested oximes. Thus, the newly developed fluorinated analogue of K203, called KR-22836, is able to slightly increase the neuroprotective effectiveness of antidotal treatment of acute tabun poisonings compared to K203 and currently available obidoxime., (© 2010 The Authors. Basic & Clinical Pharmacology & Toxicology © 2010 Nordic Pharmacological Society.)

The nerve agent VX is most likely to enter the body via liquid contamination of the skin. After percutaneous exposure, the slow uptake into the blood, and its slow elimination result in toxic levels in plasma for a period of several hours. Consequently, this has implications for the development of toxic signs and for treatment onset. In the present study, clinical signs, toxicokinetics and effects on respiration, electroencephalogram and heart rate were investigated in hairless guinea pigs after percutaneous exposure to 500 microg/kg VX. We found that full inhibition of AChE and partial inhibition of BuChE in blood were accompanied by the onset of clinical signs, reflected by a decline in respiratory minute volume, bronchoconstriction and a decrease in heart rate. Furthermore, we investigated the therapeutic efficacy of a single dose of atropine, obidoxime and diazepam, administered at appearance of first clinical signs, versus that of repetitive dosing of these drugs on the reappearance of signs. A single shot treatment extended the period to detrimental physiological decline and death for several hours, whereas repetitive administration remained effective as long as treatment was continued. In conclusion, percutaneous VX poisoning showed to be effectively treatable when diagnosed on time and when continued over the entire period of time during which VX, in case of ineffective decontamination, penetrates the skin., (Copyright 2010 Elsevier Ireland Ltd. All rights reserved.)

Objectives: Reactivation of inhibited acetylcholinesterase (AChE) with oximes is a causal therapy of intoxication with organophosphorus compounds (OPs). Maximal oxime effects are expected when effective doses are administered as soon as possible and as long as reactivation can be anticipated. An obidoxime plasma level in the range of 10-20 microM was estimated as appropriate. The achievement of this target was assessed in 34 severely OP-poisoned patients., Methods: After admission to the intensive care unit (ICU) the obidoxime regimen (250 mg i.v. as bolus, followed by 750 mg/24h) was started and maintained as long as reactivation was possible. Plasma concentrations of obidoxime were determined by HPLC., Results: A total amount of 2269+/-1726 mg obidoxime was infused over 65 h+/-55 h resulting in a steady state plasma concentration of 14.5+/-7.3 microM. Obidoxime was eliminated with t(1/2(1)) 2.2 and t(1/2(2)) 14 h. The volumes of distribution amounted to 0.32+/-0.1L/kg (V((1))) and 0.28+/-0.12 (V((2)))L/kg. Postmortem examination of tissue in one patient showed obidoxime accumulation in cartilage, kidney and liver and pointed to brain concentrations similar to plasma concentration., Conclusions: Using the suggested obidoxime regimen, the targeted plasma concentration could be achieved. Obidoxime was eliminated biphasically and was well tolerated. This result allows the recommendation of using this definite regimen for adults also in case of mass casualties., ((c) 2010 Elsevier Ireland Ltd. All rights reserved.)

The potency of newly developed bispyridinium compound K203 and its fluorinated analog KR-22836 in reactivating tabun-inhibited acetylcholinesterase and reducing tabun-induced lethal toxic effects was compared with commonly used oximes (obidoxime, trimedoxime, the oxime HI-6) using in vivo methods. Studies determining the percentage of reactivation of tabun-inhibited blood and tissue acetylcholinesterase in rats showed that the reactivating efficacy of K203 is higher than the reactivating efficacy of its fluorinated analog KR-22836 as well as currently available oximes studied. The therapeutic efficacy of the oxime K203 and its fluorinated analog corresponds to their potency to reactivate tabun-inhibited acetylcholinesterase. According to the results, the oxime K203 is more suitable than KR-22836 for the replacement of commonly used oximes for the antidotal treatment of acute tabun poisoning due to its relatively high potency to counteract the acute toxicity of tabun.

Assessment of organophosphate poisoning could benefit from a safe, non-expensive, easy to perform, quick (< 1 hour) test, which evaluates the level of cholinesterase activity "in vitro" regarding to the capability of oximes to reactivate OF-blocked cholinesterase. In the proposed protocol, 0.5 mL of sample serum is incubated, prior to the evaluation of level of cholinesterase activity, with 5 microL of a Toxogonin dilution (0.125 mg) for 30 minutes at 37 degrees C. For the standardization of the newly proposed protocol, several important issues were documented in the present article. The new original method of assessing cholinesterase reactivability will consist in an advantage for the diagnosis, prognostic evaluation and therapeutic orientation in OF intoxication.

The therapy of organophosphorus compound (OP) poisoning is still a challenge to clinical toxicologists. To alleviate peripheral respiratory failure oximes, e.g. obidoxime and pralidoxime, are used to reactivate inhibited acetylcholinesterase (AChE) with the intention to restore the disturbed neuromuscular function. In severe human OP poisoning the persistence of poison may counteract effective reactivation by oximes. Therefore, the study was designed to investigate the effect of the clinically used oximes obidoxime, pralidoxime and the experimental compounds HI 6 and HLö 7 in the presence of different paraoxon concentrations. The mouse phrenic nerve-diaphragm preparation was used as a functional model. After washout of paraoxon remarkably low concentrations of obidoxime or HLö 7 were sufficient for restoration of paraoxon-impaired muscle force. In the presence of paraoxon, obidoxime was the most effective oxime and therapeutically used concentrations (10-20microM) were able to restore muscle function even in the presence of 1microM paraoxon. HLö 7 was less effective, but superior to HI 6 and pralidoxime. Generally, a reactivation of AChE to about 30-40% of normal was sufficient for restoration of muscle force. Thus, the data presented strongly support the administration of appropriately dosed oximes, preferably obidoxime, in paraoxon-poisoned patients to restore paraoxon-impaired muscle force., (Copyright 2010 Elsevier Ireland Ltd. All rights reserved.)

The influence of the combination of oximes on the reactivating and therapeutic efficacy of antidotal treament of acute tabun poisoning was evaluated. The ability of two combinations of oximes (HI-6 + obidoxime and HI-6 + K203) to reactivate tabun-inhibited acetylcholinesterase and reduce acute toxicity of tabun was compared with the reactivating and therapeutic efficacy of antidotal treatment involving single oxime (HI-6, obidoxime, K203) using in vivo methods. Studies determining percentage of reactivation of tabun-inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the reactivating efficacy of both combinations of oximes is higher than the reactivating efficacy of the most effective individual oxime in blood and diaphragm and comparable with the reactivating effects of the most effective individual oxime in brain. Moreover, both combinations of oximes were found to be slightly more efficacious in the reduction of acute lethal toxic effects in tabun-poisoned mice than the antidotal treatment involving individual oxime. A comparison of reactivating and therapeutic efficacy of individual oximes showed that the newly developed oxime K203 is slightly more effective than commonly used obidoxime and both of them are markedly more effective than the oxime HI-6. Based on the obtained data, we can conclude that the antidotal treatment involving chosen combinations of oximes brings beneficial effects for the potency of antidotal treatment to reactivate tabun-inhibited acetylcholinesterase in rats and to reduce acute toxicity of tabun in mice.

Thirty-four adult patients with severe organophosphorus compounds (OP) poisoning requiring artificial ventilation were enrolled in a clinical study and received atropine and obidoxime (250 mg i.v., followed by 750 mg/24 h) as antidotal treatment. Here, we re-analyzed the cholinesterase status (red blood cell acetylcholinesterase (RBC-AChE) activity, reactivatability of RBC-AChE, and plasma butyrylcholinesterase (Pl-BChE) activity) in relation to the neuromuscular transmission (NMT) data. When RBC-AChE activity ranged between 100% and 30% NMT was unimpaired after tetanic stimulation with frequencies up to 50 Hz. A further decrease in RBC-AChE activity was accompanied by a marked disturbance of NMT, being strongly impaired at AChE activities <5% of normal. Higher stimulation frequencies (>30 Hz) facilitated the discrimination of the types of impairment. The neuromuscular transmission was the best quantified by using the ratio of the ninth to the first amplitude, while the standard method was less discriminative. At RBC-AChE levels higher than 40% of normal weaning from the ventilator may be considered. Completely aged RBC-AChE as indicated by loss of reactivatability loses its guidance function. Then, steadily increasing Pl-BChE activity suggests lack of circulating poison. One-week later, neuromuscular transmission may be largely normal and patients could be weaned from the respirator if other complications are not withstanding.

Organophosphate poisoning is associated with a high mortality rate due to respiratory failure, dysrhythmias, and multi-organ failure. We report two cases of survival after "in-the field" antidote treatment of very severe organophosphate poisonings. Two patients orally ingested large amounts of the organophosphorous agent oxydemeton-methyl in suicide attempts, resulting in the hypercholinergic syndrome in both. Resuscitation included early administration of antidote by emergency medical personnel as well as high-dose atropine. Plasma levels of pseudo cholinesterase were initially very low in both patients. Long-term mechanical ventilation was necessary, and both patients developed aspiration pneumonia. At discharge, no major neurological deficits were present. Prompt antidote treatment and aggressive supportive emergency and intensive care unit therapy contribute to improved survival after acute organophosphate poisoning. We believe that in cases of mass poisonings--for example, terrorist activity--therapy must be available on the scene as soon as possible. This also may require decentralized antidote storage.

Objective: The effects of obidoxime in the treatment of organophosphate poisoning were assessed by biochemical and biological effect monitoring. In this article we report effects on neuromuscular function, oxime and atropine concentration, and relate them to acetylcholinesterase (AChE) activity., Methods: We measured the activity of cholinesterase in plasma and AChE in red blood cells (RBC) and related these data with neuromuscular transmission analysis (ulnar nerve stimulation). Concomitantly, poison and oxon along with plasma obidoxime and atropine levels were measured at regular intervals., Results: We found a close correlation between RBC-AChE activity and neuromuscular transmission and a reciprocal correlation between both the atropine maintenance dose and/or its plasma concentration. The steady state of RBC-AChE activity of reactivation and re-inhibition followed the course predicted by laboratory-determined reaction constants., Conclusions: Intense monitoring of organophosphate-poisoned patients allowed assessment of why a given obidoxime concentration was, or was not, able to counteract the re-inhibition of the RBC-AChE. RBC-AChE activity mirrors the function of n-receptor- and m-receptor-mediated cholinergic signaling as measured by neuromuscular transmission and atropine requirements.

Objective: The effects of obidoxime in the treatment of organophosphate poisoning were assessed by comparing the clinical course with its effects on laboratory parameters relevant to poisoning. In this article we report clinical findings and activity of cholinesterase in plasma and acetylcholinesterase (AChE) in red blood cells. In a linked paper we describe changes in neuromuscular transmission and atropine concentrations in the same patient cohort., Methods: We studied 34 atropinized patients with severe parathion, oxydemeton methyl, and dimethoate self-poisoning who were treated with obidoxime in a standard protocol. We measured the AChE activity in blood and related it to clinical features of organophosphate poisoning., Results: Patients poisoned with parathion responded promptly to obidoxime (250 mg bolus followed by continuous infusion at 750 mg/day up to 1 week) with improvement of neuromuscular transmission and increased AChE activity. The effects were only transient in cases with the other poisons. Death (7/34) occurred late and was mostly due to complications rather than due to ongoing cholinergic crisis., Conclusions: Obidoxime appeared safe and reactivated AChE in parathion poisoning.

Introduction: Exposure to organophosphate and carbamate insecticides inhibits cholinesterase activity and interferes with synaptic transmission both centrally and peripherally at muscarinic receptors and nicotinic receptors. The study reported the usefulness of plasma cholinesterase ChE activity assays for diagnosis and the management of organophosphate and carbamate toxicity in children., Methods: A retrospective study was conducted on children with organophosphate and carbamate poisoning. Forty-seven patients were included. The diagnosis was confirmed by measuring plasma cholinesterase levels. Atropine was given intravenous (0.02 mg/kg) and repeated until secretions were controlled. Obidoxime chloride was administered as 4-8 mg/kg/dose for children with organophosphate poisoning and to those in whom the ingested material was unidentified on admission., Discussion: Most of the patients showed marked reactivation in plasma ChE within several hours and recovered completely within 24 h of admission. Complications were observed in 17 patients (36%). Mechanical ventilatory support was required in six patients. The duration intensive care stay was 3 +/- 2.4 days., Conclusion: Low plasma ChE levels support the diagnosis of insecticides poisoning, but no significant association is present between the severity of poisoning and plasma ChE levels. Atropine should be used as soon as possible to counteract the muscarinic effects. Appropriate management and early recognition of the complications may decrease the mortality rate.

Oxime reactivators HI-6, obidoxime, trimedoxime, K347 and K628 were investigated as drugs designed for treatment of tabun intoxication. The experiments were performed on rats in order to simulate real conditions. Rats were intoxicated with one LD(50 )of tabun and treated with atropine and mentioned reactivators. Activities of erythrocyte acetylcholinesterase (AChE), plasma butyrylcholinesterase (BChE) and brain AChE were measured as markers of reactivation efficacy. An estimation of low molecular weight antioxidant levels using cyclic voltammetry was the second examination parameter. The evaluation of cholinesterases activity showed good reactivation potency of blood AChE and plasma BChE by commercially available obidoxime and newly synthesized K347. The potency of oximes to reactivate brain AChE was lower due to the poor blood-brain barrier penetration of used compounds. Commercially available reactivator HI-6 and newly synthesized K628 caused oxidative stress measured by cyclic voltammetry as antioxidant level. The oxidative stress provoked by HI-6 and K628 was found to be significant on probability level P = 0.05. The others reactivators did not affect antioxidant levels., (Copyright 2009 John Wiley & Sons, Ltd.)

The ability of obidoxime with atropine and diazepam mixture to reactivate acetylcholinesterase inhibited by the organophosphorus compound chlorfenvinphos was compared in the central nervous system and peripheral tissues of rats. The animals were intoxicated with chlorfenvinphos (6 mg/kg, p.o.) and treated immediately, 24 and 48 hrs later with obidoxime (50 mg/kg, i.p.), atropine (10 mg/kg, i.p.), and diazepam (10 mg/kg, i.p.) in a single dose, or in various combinations (with 2-3 drugs) simultaneously. Total tissue acetylcholinesterase activities were monitored at 2, 72, and 168 hrs after intoxication. Enzyme activity was determined using Ellman's colorimetric method. The results of the present study show that obidoxime administered separately and jointly with atropine and diazepam 24 hrs after intoxication was effective on reactivation of chlorfenvinphos-inhibited acetylcholinesterase in the central nervous system and in the peripheral tissues. However, the application of obidoxime alone or in combination with atropine and diazepam 48 hrs after chlorfenvinphos intoxication caused an increased unfavourable effect in rats. The results obtained also indicate an unfavourable interaction of obidoxime with diazepam in the course of chlorfenvinphos poisoning, when antidotes were administered immediately, 24 and 48 hrs after intoxication.

Introduction: The ability of currently available reactivators to reactivate cyclosarin is low. The aim of this study was to determine the reactivating and therapeutic efficacy of newly developed oximes (K206, K269) compared with currently available oximes against cyclosarin., Methods: Rats and mice received atropine or atropine + oxime intramuscularly (i.m.) before or after an i.m. dose of cyclosarin. Acetylcholine activity levels in blood and tissues were measured to calculate the reactivation efficacy and potency., Results and Discussion: In vivo determined percentage of reactivation of cyclosarin-inhibited blood and tissue acetylcholinesterase (AChE) in poisoned rats showed that the potency of both newly developed oximes (K206, K269) to reactivate cyclosarin-inhibited AChE is comparable with that of obidoxime in blood and diaphragm, but slightly higher than that of obidoxime in brain. Their reactivating efficacy is significantly lower compared with that of the oxime HI-6. K206 and K269 are relatively effective in reducing cyclosarin-induced lethal toxic effects in mice. Their therapeutic efficacies exceed the therapeutic potency of obidoxime but not that of HI-6., Conclusions: K206 and K269 are as effective in the reactivation of cyclosarin-inhibited AChE in rats and in the reduction of lethal toxic effects of cyclosarin in mice as obidoxime, but because their reactivating and therapeutic potency is significantly lower than that of HI-6, they are not suitable replacements for the currently available oximes for the treatment of cyclosarin poisoning.

The neuroprotective effects of newly developed oximes (K203, K206) and commonly used oximes (obidoxime, HI-6) in combination with atropine in rats poisoned with tabun at a sublethal dose (180 microg/kg i.m.; 80% LD(50)) were studied. The tabun-induced neurotoxicity was monitored by using a functional observational battery and an automatic measurement of motor activity. The neurotoxicity of tabun was monitored at 24 hours and 7 days following tabun challenge. The results indicate that K203 and obidoxime in combination with atropine allow all tabun-poisoned rats to survive within 7 days following tabun challenge, while 2 nontreated tabun-poisoned rats and 1 tabun-poisoned rat treated with K206 or HI-6 in combination with atropine died within 7 days. Only one of the newly developed oximes (K203) combined with atropine seems to be effective for a decrease in tabun-induced neurotoxicity within 24 hours after tabun sublethal poisoning, although it is not able to eliminate tabun-induced neurotoxicity completely. On the other hand, the neuroprotective efficacy of commonly used oximes (obidoxime and HI-6), as well as one of the new synthesized oximes (K206), is significantly lower in comparison with K203, according to the number of eliminated tabun-induced neurotoxic signs at 24 hours after tabun challenge. Due to its neuroprotective effects, K203 appears to be a suitable oxime for the antidotal treatment of acute tabun poisonings.

Study Objective: Unintentional pediatric exposure to insecticides is common in developing countries. A clinical decision aid could guide early triage decisionmaking., Methods: Study design was prospective observational data collection in a specialty poisoning hospital in Cairo, Egypt. Patients were children 2 months to 59 months of age, without pretreatment, presenting within 2 hours of an exposure to an organophosphate or carbamate insecticide. A resource-requiring course was defined as any occurrence of hypoxia, use of atropine or obidoxime, use of ICU care, or death. The goal of analysis was derivation of a clinical decision aid to predict a resource-requiring course with 100% sensitivity., Results: During the 21-month study, 197 children 2 months to 59 months of age exposed to an organophosphate or carbamate insecticide were treated at the center. One hundred two of these children met the study inclusion criteria: 95 had parental consent and completed the study observation period of which 65 used resources (4 died). All patients who ultimately met resource-requiring criteria initially did so at arrival. Pinpoint pupil alone identified 63 of 65 of these patients yet wrongly identified only 5 of 30 minimally ill patients. Pinpoint pupil or diarrhea identified 65 of 65 patients with a resource-requiring course while identifying 7 of 30 patients with a non-resource-requiring course (sensitivity 1.00; 95% confidence interval 0.95 to 1.00; specificity 0.77; 95% confidence interval 0.58 to 0.90)., Conclusion: Using 2 features, pinpoint pupils and diarrhea, we identified at presentation all patients who ultimately had a course using medications or advanced resources. According to this preliminary study, symptoms occur rapidly, so using an early triage aid may be feasible. A validation study is necessary.

beta-glucuronidase is considered a sensitive biomarker for acute organophosphorus poisoning. In this well-documented study, multiple plasma samples over time were collected. A decrease in plasma concentration of beta-glucuronidase was surprisingly observed, even within normal range. These findings do not support the hypothesis that beta-glucuronidase is a useful biomarker for acute organophosphorus poisoning in humans.

The potency of newly developed monoxime bispyridinium compounds (K156, K203) in reactivating tabun-inhibited acetylcholinesterase and reducing tabun-induced lethal toxic effects was compared with commonly used oximes (obidoxime, trimedoxime, the oxime HI-6) using in vivo methods. Studies determining percentage of reactivation of tabun-inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the reactivating efficacy of newly developed oxime K203 is comparable with obidoxime and trimedoxime in blood and higher than the reactivating potency of trimedoxime and obidoxime in diaphragm and brain, where the difference in reactivating efficacy of obidoxime, trimedoxime and K203 is significant. On the other hand, the potency of newly developed K156 to reactivate tabun-inhibited acetylcholinesterase is comparable with obidoxime or trimedoxime in diaphragm and brain. It is significantly lower than the reactivating efficacy of trimedoxime and obidoxime in blood. Moreover, both newly developed oximes were found to be relatively efficacious in the reduction of lethal toxic effects in tabun-poisoned mice. Especially, the oxime K203 is able to decrease the acute toxicity of tabun nearly two times. The therapeutic efficacy of K156 and K203 corresponds to their potency to reactivate tabun-inhibited acetylcholinesterase, especially in diaphragm and brain. In contrast to obidoxime and trimedoxime, the oxime HI-6 is not effective in reactivation of tabun-inhibited acetycholinesterase and in reducing tabun lethality. While the oxime K156 does not improve the reactivating and therapeutic effectiveness of currently available obidoxime and trimedoxime, the newly developed oxime K203 is markedly more effective in reactivation of tabun-inhibited acetylcholinesterase in rats, especially in brain, and in reducing lethal toxic effects of tabun in mice and, therefore, it is suitable for the replacement of commonly used oximes for the antidotal treatment of acute tabun poisoning.

The neuroprotective effects of newly developed oximes (K074, K075) and currently available oximes (obidoxime, HI-6) in combination with atropine in rats poisoned with tabun at a sublethal dose (180 micro g/kg i.m.; 80% LD(50)) were studied. The tabun-induced neurotoxicity was monitored using a functional observational battery and an automatic measurement of motor activity. The neurotoxicity of tabun was monitored at 24h and 7 days following tabun challenge. The results indicate that all oximes studied in combination with atropine allow all tabun-poisoned rats to survive within 7 days following tabun challenge while two non-treated tabun-poisoned rats died within 2h. Both newly developed oximes combined with atropine seem to be effective antidotes for a decrease in tabun-induced neurotoxicity in the case of sublethal poisoning although they are not able to eliminate tabun-induced neurotoxicity completely. The oxime K075 showed a higher neuroprotective efficacy against tabun than K074 according to the number of eliminated tabun-induced neurotoxic signs at 24h as well as 7 days after tabun challenge. The neuroprotective efficacy of obidoxime in combination with atropine is similar to the potency of newly developed oxime K075 but the ability of the oxime HI-6 to counteract tabun-induced acute neurotoxicity is significantly lower at 24h as well as 7 days after tabun poisoning. Due to their neuroprotective effects, both newly developed oximes (especially K075) appear to be more suitable oximes for the antidotal treatment of acute tabun poisonings than the oxime HI-6.

The neuroprotective effects of newly developed oximes (K074, K075) and currently available oximes (obidoxime, HI-6) in combination with atropine in rats poisoned with soman were studied. The soman-induced neurotoxicity was monitored using a functional observational battery at 24 h and 7 days after soman challenge. The results indicate that the oxime HI-6 combined with atropine seems to be an effective antidote for a decrease in soman-induced neurotoxicity, whereas the ability of both newly developed oximes (K074, K075) as well as obidoxime to counteract soman-induced acute neurotoxicity is negligible. Due to the absence of their neuroprotective potency, both newly developed oximes are not suitable oximes for antidotal treatment after exposure to soman. The oxime HI-6 is still the best acetylcholinesterase reactivator for the antidotal treatment of acute poisonings with soman.

Following repeated antidotal treatment of anaesthetized dogs (1 min with atropine, 10 min with atropine and obidoxime, 60 min with atropine and obidoxime) after the intoxication with soman, sarin and VX (1 x LD50, i.m.), the blood cholinesterases (erythrocyte, whole blood, plasma) were monitored and their reactivatability (whole blood) was determined. During this treatment, the activities of erythrocyte acetylcholinesterase (AChE), plasma butyrylcholinesterase (BuChE) and whole blood cholinesterases were monitored. Atropine and obidoxime did not affect cholinesterase activities in control animals, whereas administration of obidoxime to dogs intoxicated with nerve agent caused an increase in the cholinesterase activities. The sensitivity of cholinesterases decreased in the order erythrocyte AChE > whole blood cholinesterases > plasma BuChE, respectively. Following sarin intoxication, blood cholinesterases were increased after the obidoxime administration. Intoxication with VX showed a similar picture but reactivation after the obidoxime administration was greater. In soman intoxication, the picture of cholinesterase changes was similar during the first 30 min of treatment. Then the increase in AChE activity following obidoxime administration was not as high as in the case of sarin and VX intoxication. Thus, the reactivation efficacy of obidoxime during nerve agent intoxication indicates that its repeated administration could be easily monitored using the reactivation test., (Copyright 2006 John Wiley & Sons, Ltd.)

This paper discusses the toxicity and antidotal effects of 32 compounds. Screening studies have shown that these compounds combined with atropine are effective antidotes against the organophosphate nerve agents Tabun and/or Soman, having a therapeutic factor equal or greater than 2.0 when tested in mice or rats. We analysed the results of these studies, and recommend that these compounds should be studied in more detail simultaneously with conventional antidotes (PAM-2, HI-6, Toxogonin, TMB-4) in order to assess whether they could broaden the choice of compounds now available for the treatment of organophosphate poisoning.

Objective: The status of oximes in human organophosphate poisoning is controversial. This analysis compares the outcomes of therapy with or without oximes., Design: Quantitative analysis using meta-analytic techniques., Methods: Controlled trials of oximes in human organophosphate poisoning were identified by search of MEDLINE and TOXLINE (1966 to May 2005) and review of published articles., Measurements and Main Results: Of the 3,122 articles on organophosphate poisoning identified by electronic search, 116 related to oxime use in human organophosphate poisoning. Seven trials, including two randomized controlled trials, compared oximes with standard medical care. Varying dosage schedules of pralidoxime or obidoxime were used. The effects of oxime therapy on mortality rate, mechanical ventilation, incidence of intermediate syndrome, and need for intensive care therapy were analyzed and expressed as risk difference (positive values indicating oxime harm). The random effects estimator was reported because of underlying heterogeneity of treatment effects between study types. No statistically significant association of oxime therapy was demonstrated for either mortality (risk difference 0.09, 95% confidence interval -0.08 to 0.27), ventilatory requirements (risk difference 0.16, 95% confidence interval -0.07 to 0.38), or the incidence of intermediate syndrome (risk difference 0.16, 95% confidence interval -0.12 to 0.45), although point estimates of effect suggested harm. An increased need for intensive care therapy (risk difference 0.19, 95% confidence interval 0.01 to 0.36) was apparent with oxime therapy., Conclusions: Based on the current available data on human organophosphate poisoning, oxime was associated with either a null effect or possible harm. The lack of current prospective randomized controlled trials, with appropriate patient stratification, mandates ongoing assessment of the role of oximes in organophosphate poisoning.

The present study was performed to assess and compare a therapeutic efficacy of obidoxime, HI-6, BI-6 and HS-6 administered in equimolar doses and combined with atropine in cyclosarin-poisoned mice and rats. It was demonstrated that all the therapeutic regimens tested, were able to decrease the cyclosarin-induced toxicity significantly - at least 1.5 times. Higher therapeutic ratios, almost three times, were achieved in rats in comparison with mice. The highest therapeutic ratio was achieved for therapeutic regimen consisting of HI-6 and atropine in both mice and rats. Obidoxime was the least effective oxime in the treatment of cyclosarin intoxication. The BI-6 oxime was significantly more efficacious than obidoxime (in both mice and rats) and HS-6 (in rats) but its effectiveness did not reach the efficacy of HI-6.

The mechanism of intoxication with organophosphorus compounds, including highly toxic nerve agents and less toxic pesticides, is based on the formation of irreversibly inhibited acetylcholinesterase, which causes cumulation of neuromediator acetylcholine in synaptic clefts and subsequent overstimulation of cholinergic receptors, that is followed by a generalized cholinergic crisis. Nerve agent poisoning is conventionally treated using a combination of a cholinolytic (atropine mostly) to counteract the accumulation of acetylcholine and acetylcholinesterase reactivators (pralidoxime or obidoxime) to reactivate inhibited acetylcholinesterase. In this study of cyclosarin poisoning treatment, oximes of different chemical structures (obidoxime, HI-6, BI-6, and HS-6) were tested in vitro on rat brain acetylcholinesterase (enzyme source: rat brain homogenate), and afterwards, they were tested in vivo in equimolar doses, in mice and rats. The HI-6 oxime appeared to be the most effective oxime in vitro and in vivo.

Organophosphorus chemicals (OPs) are the pesticides most often involved in serious human poisoning. Treatment of intoxication with OPs conventionally involves atropine for reduction of muscarinic signs and oximes that increase the rate of hydrolysis of the phosphorylated enzyme acetylcholinesterase (AChE). Although atropine and oximes (pralidoxime or obidoxime) are traditionally used in the management of such poisoning, their efficacy remains a major issue of debate; thus, the goal of this prospective clinical trial was to elaborate the value of magnesium sulfate (MgSO4) in the management and outcome of OP insecticide poisoning. This unicenter, randomized, single-blind trial study was conducted on patients who were acutely poisoned with OPs and admitted to the Poisoning Center of Loghman-Hakim Hospital in Tehran, Iran. In a systematic sampling, every fourth eligible patient was chosen to undergo MgSO4 treatment. Magnesium sulfate was administered at dose of 4 g/day i.v. continued for only the first 24 hours after admission. The mean daily oxime requirement and the mean daily atropine requirement were not statistically significant between two treated groups. The mortality rate and hospitalization days of patients who received MgSO4 treatment were significantly lower than those who had not received MgSO4 (P < 0.01). It is concluded that administration of MgSO4, in a dose of 4 g/day concurrent to conventional therapy, in OP acute human poisoning is beneficial by reducing the hospitalization days and rate of mortality.

1. To study the influence of antidotes on tabun-induced neurotoxicity, the rats were injected intramuscularly with organophosphate tabun (LD50). The efficacy of choice antidotal treatment consisting of acetylcholinesterase reactivator obidoxime and one of four anticholinergic drugs (atropine, benactyzine, biperiden, scopolamine) was compared. 2. Testing of tabun-induced neurotoxicity progress was carried out using the method Functional observational battery. The experimental animals as well as controls were observed at 24 hours and 7 days following tabun or saline administration. 3. The results were compared to the condition of animals without anticholinergic drug (oxime alone) and control rats that received physiological solution instead of tabun and treatment. Antidotal treatment involving centrally acting anticholinergic drugs (benactyzine, biperiden, scopolamine) showed significantly higher neuroprotective efficacy compared to antidotal treatment containing atropine.

The neuroprotective effects of antidotes (atropine, pralidoxime/atropine, obidoxime/atropine and HI-6/atropine mixtures) on rats poisoned with tabun at a lethal dose (220 microg/kg intramuscularly; 100% of LD50 value) were studied. The tabun-induced neurotoxicity was monitored using a functional observational battery and an automatic measurement of motor activity. The neurotoxicity of tabun was monitored at 24 hr and 7 days after tabun challenge. The results indicate that atropine alone is not able to protect the rats from the lethal effects of tabun. Three non-treated tabun-poisoned rats and one tabun-poisoned rat treated with atropine alone died within 24 hr. On the other hand, atropine combined with all tested oximes allows all tabun-poisoned rats to survive at least 7 days following tabun challenge. Obidoxime combined with atropine seems to be the most effective antidotal treatment for the elimination of tabun-induced neurotoxicity in the case of lethal poisoning among tested antidotal mixtures. The antidotal mixture consisting of atropine and HI-6 is significantly less effective than the combination of atropine with obidoxime in the elimination of tabun-induced neurotoxicity in rats at 24 hr following tabun challenge. Pralidoxime in combination with atropine appears to be practically ineffective to decrease tabun-induced neurotoxicity at 24 hours as well as 7 days following tabun poisoning. Due to its neuroprotective effects, obidoxime seems to be the most effective and most suitable oxime for the antidotal treatment of acute tabun exposure among currently used oximes. Thus, the replacement of obidoxime by a more effective acetylcholinesterase reactivator for soman poisoning, the oxime HI-6, can to a small extent diminish the neuroprotective efficacy of antidotal treatment in the case of acute tabun poisonings.

To study the influence of pharmacological pretreatment (PANPAL) and antidotal treatment (obidoxime plus atropine) on tabun-induced neurotoxicity, male albino rats were poisoned with a lethal dose of tabun (280 microg/kg i.m.; 100% of LD(50) value) and observed at 24 h and 7 days following tabun challenge. The neurotoxicity of tabun was evaluated using a functional observational battery (FOB) and an automatic measurement of motor activity. Pharmacological pretreatment as well as antidotal treatment were able to eliminate most of tabun-induced neurotoxic effects observed at 24 h following tabun poisoning. However, there was not significant difference between the efficacy of PANPAL and antidotal treatment to eliminate tabun-induced neurotoxicity in rats. The combination of PANPAL pretreatment and antidotal treatment seems to be slightly more effective in the elimination of tabun-induced neurotoxicity in rats at 24 h following tabun challenge in comparison with the administration of PANPAL pretreatment or antidotal treatment alone. At 7 days following tabun poisoning, very few neurotoxic signs in tabun-poisoned rats were observed regardless of administration of pharmacological pretreatment or antidotal treatment. Thus, our findings confirm that the combination of pharmacological pretreatment and antidotal treatment is not only able to protect the experimental animals from the lethal effects of tabun but also to eliminate most of tabun-induced signs of neurotoxicity in tabun-poisoned rats.

The mortality rate of suicidal parathion poisoning is particularly high, the onset of fulminant cholinergic signs, and the patients frequently present to the emergency physician with life-threatening symptoms. Despite this uniformity, subsequent clinical course differs significantly among patients, mostly not as a result of different delays in treatment or insufficiency of primary care. Probably, the differences depend on the amount of poison absorbed and/or the disposition of the active poison, paraoxon. We followed the toxicokinetics of parathion and tried to quantify the actual poison load. To this end, we monitored parathion-intoxicated patients (patients requiring artificial ventilation) for plasma levels of parathion and paraoxon along with the activity of erythrocyte acetylcholinesterase and its reactivatability. Plasma obidoxime concentrations were followed as well as the cumulative urinary para-nitrophenol conjugate excretion as a measure of total poison load. All patients received a standard obidoxime scheme of a 250 mg bolus dose intravenously, followed by continuous infusion with 750 mg per 24 hours as long as reactivation could be expected (usually 1 week). All other treatment was instituted as judged by the physician. It was recommended to use atropine at low doses to achieve dry mucous membranes, no bronchoconstriction and no bradycardia. Usually 1-2 mg/h were sufficient. Seven selected cases are presented exemplifying toxicokinetic peculiarities. All patients were severely intoxicated, while the amount of parathion absorbed varied widely (between 0.12 and 4.4 g; lethal dose 0.02-0.1 g) and was generally much lower than anticipated from the reports of relatives. It remains open whether the discrepancies between reports and findings were due to exaggeration or to effective decontamination (including spontaneous vomiting, gastric lavage and activated charcoal). Absorption of parathion from the gastrointestinal tract was sometimes retarded, up to 5 days, resulting in fluctuating plasma profiles. The volume of distribution at steady-state (Vdss) of parathion was around 20 L/kg. Post-mortem analysis in one patient revealed a 66-fold higher parathion concentration in fat tissue compared with plasma, 16 days after ingestion. Biotransformation of parathion varied widely and was severely retarded in one patient receiving fluconazole during worsening of renal function, while phenobarbital (phenobarbitone) sedation (two cases) had apparently no effect. The proportion of plasma parathion to paraoxon varied from 0.3-30, pointing also to varying paraoxon elimination, as illustrated by one case with particularly low paraoxonase-1 activity. Obidoxime was effective at paraoxon concentrations below 0.5 microM, provided aging was not too advanced. This concentration correlated poorly with the paration concentration or the poison load. The data are discussed in light of the pertinent literature.

A 50-year-old man swallowed 200 ml of an insecticide containing the organophosphates dimethoate and phenitrotion in an attempted suicide. On admission, signs of a cholinergic syndrome were observed: miosis, rhinorrhoea, and fasciculations. This was followed by bradycardia with hypotension and vomiting. The patient was treated with the antidotes atropine and obidoxime. Decreasing consciousness necessitated intubation, mechanical ventilation and other supportive measures. Although the serum concentrations of both organophosphate compounds rapidly decreased, the activity of cholinesterase showed a prolonged inhibition. The clinical course was complicated by hypotension, acute respiratory distress syndrome, nosocomial pneumonia, and an epileptic seizure. A period with muscle weakness and a persisting depressive disorder then followed. This case is characteristic for acute intoxications with irreversible acetylcholinesterase inhibitors, such as organophosphate compounds. The treatment of these potentially severe intoxications includes rapid decontamination and the administration of high doses of atropine followed by obidoxime. Mechanical ventilation and circulatory support are also indicated.

This report presents a non-lethal method for estimating a range of therapeutic doses of bisquaternary oximes that serve as antidotes against organophosphorus poisoning. We have estimated therapeutic oxime doses that are equivalent in their relative toxicity rather than selecting arbitrary fractions of their LD(50). Thus, toxic signs of the oximes HI-6, HLö-7, Toxogonin, AB-8 and AB-13 were monitored quantitatively in baboon monkeys and beagle dogs. Using Toxogonin as a reference oxime, a calculated unit of equivalent dose (CED) was defined as the oxime dose equal to the ratio between its minimal toxic dose (MTD) and the therapeutic ratio (TR) of Toxogonin i.e. CED = MTD/TR. Assuming that the tails of dose-response curves of toxicity for bisquaternary oximes are shallow and similar to one another, one could substitute the ED(10) for the MTD. The ED(10) values for bisquaternary oximes were estimated using the log-log model following experimental observations and quantitative scoring of toxic signs in dogs and monkeys. The MTD values then were calculated using the ED(10) values and the experimental therapeutic dose of the reference oxime Toxogonin. The following CED values were obtained for AB-8, AB-13, Toxogonin, HI-6 and HLö-7 in dogs (d) and monkeys (m): 98.7, 74.2, 30.0, 14.5 and 12.1 (d) and 281.9, 232.1, 41.7, 192.9 and 92.9 (m) micromol kg(-1), respectively. The antidotal efficacy of these oximes against poisoning by the nerve agent tabun was determined in dogs and monkeys. These dose-dependent efficacy data were obtained at 0.3 x CED, 1 x CED and 3 x CED of oximes in combination with atropine. These data provide comparative therapeutic values using oxime doses based on their relative toxicity. The highest antidotal efficacy against tabun in dogs was obtained for toxogonin, whereas HLö-7 and AB-13 were most efficacious in monkeys., (Copyright 2001 John Wiley & Sons, Ltd.)

A couple showing signs of cholinergic crisis was admitted to the hospital. Analyses with high-performance liquid chromatography and gas chromatography-mass spectrometry conducted on serum, urine, and stomach contents that were collected few hours after first symptoms showed the presence of aldicarb, which is the most potent carbamate insecticide on the market. A murder attempt was suspected because the patients showed the first signs some minutes after drinking coffee upon returning home and no commercial products containing aldicarb were found in the house. Because of the reversibility of inhibition of acetylcholinesterase, the patients recovered after treatment with atropine and toxogonin. They left the hospital after 12 days. To our knowledge, the serum concentrations of aldicarb reported in this paper are the highest reported for a nonfatal case.

Considering the various microscopic reactions as well as toxicokinetic and pharmacokinetic principles in therapy of organophosphate poisoning, the administration of obidoxime by an initial bolus dose followed by continuous infusion appears rational. Using this protocol, six patients each with parathion or oxydemeton methyl poisoning were treated. In parathion poisoning, reactivation was possible up to 7 days. At paraoxon concentrations > 0.1 microM obidoxime only partially reactivated acetylcholinesterase (AChE) of erythrocytes in vivo although reactivation could be assessed in vitro, which roughly fitted theoretical calculations. AChE-inhibitory material was detected up to 5 days. Cholinergic signs soon subsided when AChE was above 20% of normal, and atropine plasma levels could be kept below 7 ng/ml. In one patient brain damage persisted. Oxydemeton methyl poisoning responded to obidoxime therapy only when the oxime was instituted shortly after poisoning. Out of six patients one died. No intermediate syndrome and no signs of permanent hepatic dysfunction were found in the 12 patients.

1. The neuroprotective effects of antidotes (atropine, obidoxime/atropine mixture, HI-6/atropine mixture) on rats poisoned with soman at a sublethal dose (48 micrograms/kg i.m.; 60% of LD50 value) were studied. The neurotoxicity was monitored using a functional observational battery (FOB) and an automatic measurement of motor activity. The neurotoxicity of soman was monitored at 24 h and 7 d following soman poisoning. 2. The results indicate that atropine alone and the oxime HI-6 in combination with atropine seem to be effective antidotal treatment for the elimination of soman-induced neurotoxicity in the case of sublethal poisonings. 3. On the other hand, the combination of obidoxime with atropine appears to be practically ineffective in diminishing neurotoxic soman-induced symptoms. 4. Dealing with neuroprotective effects of antidotes, the oxime HI-6 in combination with atropine seems to be more suitable antidotal mixture than obidoxime in combination with atropine even in the case of sublethal poisoning with nerve agents.

Organophosphate (OP) compounds have been used as pesticides and in chemical warfare (nerve agents). Two nerve agents, tabun and sarine, were used by the Iraqi army against Iranian troops and innocent people. Hundreds of the exposed combatants died in the field. Atropine sulphate has been used successfully in large doses to counteract the muscarinic effects of OP poisoning. The effects of oximes in human OP poisoning have not been well studied. Our aim was to study the effects of obidoxime and pralidoxime in OP pesticide poisoning. The patients were divided into three groups: atropine (A), obidoxime + atropine (OA) and pralidoxime + atropine (PA). Sixty-three patients (33 males, 30 females) with a mean age of 25 years were studied in different groups (43 A, 22 OA and 8 PA). There were no statistical significant differences in major clinical findings and acetylcholinesterase (AChE) activity on admission between the groups. Significant changes were observed during the treatment. Notwithstanding the severity of intoxication--particularly respiratory complications were more observed in the OA and PA groups--there were no fatalities in the PA group, whereas 4 (9%) and 6 (50%) patients in the A and OA groups died, respectively. AChE reactivation was only observed in the PA group, although it was not statistically significant (r = 0.4747). There was a good relationship between the AChE reactivation and outcome of the patients. High doses of obidoxime (8 mg/kg followed by 2 mg/kg/h) were found to be hepatotoxic and should be avoided. High doses of pralidoxime (30 mg/kg followed by 8 mg/kg/h) did not induce serious side effects and may be effective in some OP pesticides poisoning.

A previously healthy 2-y-old boy was admitted to the hospital 30 min after the ingestion of 10 ml of demeton-S-methyl (META-SYSTOX). Treatment consisted of gastric decontamination, atropine, reactivator (obidoxime) and supportive therapy. Atropine was given to control the muscarinic features. Assisted ventilation was required for 6 h; however, this treatment was able to be discontinued following the second injection of obidoxime 11.5 h after the ingestion. Excess salivation and slight bradycardia were easily controlled with small doses of atropine for 5 d following admission to Ullevaal Hospital. Further course was uneventful, and the patient was discharged on the 8th d without any sequelae. Plasma cholinesterase levels were initially low (<400 U/l), but returned to reference values upon discharge. In this case, adequate supportive therapy and the rapid administration of both atropine and obidoxime were clearly associated with a favorable outcomes

1. The influence of three oximes (obidoxime, HI-6 and the new asymmetric bispyridinium oxime BI-6) in combination with atropine on soman-induced cholinergic and stressogenic effects in rats was studied. 2. The oxime BI-6 produced significantly higher reactivation of soman-inhibited blood and diaphragm cholinesterases than obidoxime. On the other hand, its reactivating effect was not so high as the effect of the oxime HI-6. 3. There were not significant differences in the reactivation of soman-inhibited brain acetylcholinesterase among all three oximes tested. 4. The influence of the oxime BI-6 on soman-induced stressogenic effects was greater than the antistressogenic effects of HI-6 or obidoxime at 1 h or 3 h following soman poisoning. 5 These findings confirm that the oxime BI-6 has no definite advantages over HI-6 in the antidotal treatment of soman poisoning but BI-6 is significantly more effective in rats than obidoxime, one of the oximes presently in use.