N-acetylcysteine as a potentially safe adjuvant in the treatment of neurotoxicity due to pirimiphos-methyl poisoning.

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.

Carrion decomposition and assemblage of necrophagous dipterans associated with Terbufos (Organophosphate) intoxicated rat carcasses.

Organophosphate use represents one of the main causes of intentional and accidental poisoning in Brazil. Because they induce alteration in carcass decomposition and succession of necrophagous Diptera, they are important investigative tool in forensic entomology for determining the postmortem interval (PMI) and cause of death. Thus, this work aimed to evaluate the influence of Terbufos, the most commonly used organophosphate for suicides in Rio Grande do Norte, Brazil, in the decomposition process and necrophagous fly assemblies in intoxicated rat carcasses. For this, 150g female Wistar rats received, by gavage, 200µL of Terbufos (5mg/kg or 10mg/kg) or distilled water (control). Approximately 30 minutes after administration, animals were euthanized and distributed in suspended traps to decompose under environmental conditions. Decomposition was monitored daily, with photographic record and collection of the visiting dipterofauna until the dry phase. Data show that the higher dose of Terbufos i) accelerates carcass decomposition in 24h; ii) decreases the species richness and abundance of scavengers flies when compared to the control; iii) changes the succession pattern, delaying the arrival of important species for the PMI estimate and iv) causes 8% mortality of the visiting dipterofauna. This work provides relevant information about dipteran assemblages and changes in the cadaver decomposition process associated with Terbufos intoxication, which may assist in future investigative processes with suspected organophosphate poisoning.

A catalytic bioscavenger with improved stability and reduced susceptibility to oxidation for treatment of acute poisoning with neurotoxic organophosphorus compounds.

Organophosphorus (OP)1 nerve agents pose a severe toxicological threat, both after dissemination in military conflicts and by terrorists. Hydrolytic enzymes, which may be administered into the blood stream of victims by injection and can decompose the circulating nerve agent into non-toxic metabolites in vivo, could offer a treatment. Indeed, for the phosphotriesterase found in the bacterium Brevundimonas diminuta (BdPTE),2 engineered versions with improved catalytic efficiencies have been described; yet, their biochemical stabilities are insufficient for therapeutic use. Here, we describe the application of rational protein design to develop novel mutants of BdPTE that are less susceptible to oxidative damage. In particular, the replacement of two unpaired cysteine residues by more inert amino acids led to higher stability while maintaining high catalytic activity towards a broad spectrum of substrates, including OP pesticides and V-type nerve agents. The mutant BdPTE enzymes were produced in Escherichia coli, purified to homogeneity, and their biochemical and enzymological properties were assessed. Several candidates both revealed enhanced thermal stability and were less susceptible to oxidative stress, as demonstrated by mass spectrometry. These mutants of BdPTE may show promise for the treatment of acute intoxications by nerve agents as well as OP pesticides.

Differences in biological activities between recombinant human paraoxonase 1 (rhPON1) subtype isozemys R/Q as antidotes against organophosphorus poisonings.

Paraoxonase 1 (PON1) is a type of aromatic esterase widely existing in mammals. It can hydrolyze various kinds of compounds effectively in vivo and in vitro. Previous studies have confirmed that PON1 can be used as antidote against organophosphorus poisonings (OPs). In this study, we obtained two subtype isozymes (i.e. rhPON1R192 and rhPON1Q192) by gene recombination and compared their detoxification effects against different OPs in rats. The rhPON1R192 demonstrated better detoxification effect against chlorpyrifos poisoning than the rhPON1Q192, whose detoxification effect against diazinon poisoning was prior to the former. Both of them showed poor detoxification effect against trithion. Therefore, we concluded that, to different OPs, better detoxification effect may be achieved by selecting the PON1 subtype isozyme with higher specific hydrolytic activity.

Butyrylcholinesterase, a stereospecific in vivo bioscavenger against nerve agent intoxication.

Human butyrylcholinesterase (E.C. 3.1.1.8) purified from blood plasma has previously been shown to provide protection against up to five and a half times the median lethal dose of an organophosphorus nerve agent in several animal models. In this study the stoichiometric nature of the protection afforded by human butyrylcholinesterase against organophosphorus nerve agents was investigated in guinea pigs. Animals were administered human butyrylcholinesterase (26.15 mg/kg ≡ 308 nmol/kg) by the intravascular or intramuscular route. Animals were subsequently dosed with either soman or VX in accordance with a stage-wise adaptive dose design to estimate the modified median lethal dose in treated animals. Human butyrylcholinesterase (308 nmol/kg) increased the median lethal dose of soman from 154 nmol/kg to 770 nmol/kg. Comparing the molar ratio of agent molecules to enzyme active sites yielded a stoichiometric protective ratio of 2:1 for soman, likely related to the similar stereoselectivity the enzyme has compared to the toxic target, acetylcholinesterase. In contrast, human butyrylcholinesterase (308 nmol/kg) increased the median lethal dose of VX from 30 nmol/kg to 312 nmol/kg, resulting in a stoichiometric protective ratio of only 1:1, suggesting a lack of stereoselectivity for this agent.

Medicolegal implication of an autopsy case of methidathion ingestion.

We present an autopsy case involving ingestion of methidathion, an organothiophosphate pesticide. A headspace gas chromatography mass spectrometry system was used for screening of volatile compounds. Subsequent toxicological analysis was performed using liquid chromatography tandem mass spectrometry. Xylene and ethylbenzene were detected in stomach contents. We also identified methidathion at concentrations of 3.07 and 2240 µg/ml in femoral venous blood and stomach contents, respectively. We concluded that the victim ingested methidathion insecticide, with an estimated dose of at least 9.2 g.

Postmortem distribution of acephate and its metabolite methamidophos in body fluids and organ tissues of an intoxication case.

We herein report an intoxication case caused by the ingestion of the pesticide Ortoran®, which consists of 50% acephate aqueous solution. A man in his 60 s was found dead in his car with a 100-mL bottle containing approximately 50 mL of Ortoran®. In a gas chromatography - mass spectrometry (GC-MS) screening test, acephate and its metabolite methamidophos were qualitatively detected in his stomach contents. The amounts of acephate and methamidophos (µg/g) in the extract of each body fluid or organ tissue were measured using GC-MS and were as follows: 35.8, 2.84 (heart blood); 44.0, 2.26 (peripheral blood); 2,240, 2.79 (urine); 53.1, 8.91 (brain occipital lobe); 43.7, 2.95 (liver); 102.3, 8.02 (right kidney); and 5450, 22.9 (stomach contents). Based on these results and autopsy findings, the cause of death was concluded to be acute fatal intoxication caused by the pesticide containing acephate and its active metabolite, methamidophos. Concentration ratios between acephate and methamidophos in each body fluid and organ tissue showed higher relative concentrations of brain methamidophos to acephate than those of other organ tissues. A high relative concentration of brain methamidophos may contribute to the intoxication of acephate in humans.

COPD and asthma therapeutics for supportive treatment in organophosphate poisoning.

Context: Nerve agents like sarin or VX have repeatedly been used in military conflicts or homicidal attacks, as seen in Syria or Malaysia 2017. Together with pesticides, nerve agents assort as organophosphorus compounds (OP), which inhibit the enzyme acetylcholinesterase. To counteract subsequent fatal symptoms due to acetylcholine (ACh) accumulation, oximes plus atropine are administered, a regimen that lacks efficacy in several cases of OP poisoning. New therapeutics are in development, but still need evaluation before clinical employment. Supportive treatment with already approved drugs presents an alternative, whereby compounds from COPD and asthma therapy are likely options. A recent pilot study by Chowdhury et al. included ß2-agonist salbutamol in the treatment of OP-pesticide poisoned patients, yielding ambiguous results concerning the addition. Here, we provide experimental data for further investigations regarding the value of these drugs in OP poisoning. Methods: By video-microscopy, changes in airway area were analyzed in VX-poisoned rat precision cut lung slices (PCLS) after ACh-induced airway contraction and subsequent application of selected anticholinergics/ß2-agonists. Results: Glycopyrrolate and ipratropium efficiently antagonized an ACh-induced airway contraction in VX-poisoned PCLS (EC50 glycopyrrolate 15.8 nmol/L, EC50 ipratropium 2.3 nmol/L). ß2-agonists formoterol and salbutamol had only negligible effects when solely applied in the same setting. However, combination of formoterol or salbutamol with low dosed glycopyrrolate or atropine led to an additive effect compared to the sole application [50.6 ± 8.8% airway area increase after 10 nmol/L formoterol +1 nmol/L atropine versus 11.7 ± 9.2% (10 nmol/L formoterol) or 8.6 ± 5.9% (1 nmol/L atropine)]. Discussion: We showed antagonizing effects of anticholinergics and ß2-agonists on ACh-induced airway contractions in VX-poisoned PCLS, thus providing experimental data to support a prospective comprehensive clinical study. Conclusions: Our results indicate that COPD and asthma therapeutics could be a valuable addition to the treatment of OP poisoning.

Superior efficacy of HI-6 dimethanesulfonate over pralidoxime methylsulfate against Russian VX poisoning in cynomolgus monkeys (Macaca fascicularis).

Organophosphorus nerve agents still represent a serious risk to human health. In the French armed forces, the current emergency treatment against OP intoxications is a fully licensed wet-dry dual-chambered autoinjector (Ineurope ®), that contains pralidoxime methylsulfate (2-PAM) to reactivate inhibited acetylcholinesterase (AChE), atropine sulfate (AS) and avizafone chlorhydrate (AVZ). While this treatment is effective against several of the known nerve agents, it shows little efficacy against the Russian VX (VR), one of the most toxic compounds. HI-6 dimethanesulfonate (HI-6 DMS) is an oxime able to reactivate in vitro and in vivo VR-inhibited AChE. To confirm the superiority of HI-6 DMS towards 2-PAM prior to licensing, we compared the two 3-drug-combinations (HI-6 vs 2-PAM, 33 and 18 mg/kg respectively, equimolar doses; AS/AVZ 0.25/0.175 mg/kg respectively) in VR-poisoned cynomolgus macaques, the model required by the French drug regulatory agency. In parallel we performed HI-6 pharmacokinetics analysis using a one compartment model. A better efficacy of the HI-6 DMS combination was clearly observed: up to 5 LD50 of VR (i.m.), a single administration of the HI-6 DMS combination, shortly after the onset of clinical signs, prevented death of the four intoxicated animals. Conversely 2-PAM only prevented death in one out of three subjects exposed to the same amount of VR. As expected with V agents, reinhibition of blood AChE was observed but without any apparent impact on the clinical recovery of the animals. A single administration of the HI-6 DMS combination was still but partially effective at 15 LD50 of VR, allowing a 50% survival rate.

Fatal Poisoning with Both Dichlorvos and Phenthoate.

Organophosphates are widely used as pesticides. However, organophosphates are occasionally orally ingested to commit suicide. In this case, a man in his late 80s committed suicide by ingesting both dichlorvos and phenthoate. Autopsy findings revealed a characteristic volatile odor from his mouth, stomach, lungs, liver, and kidneys. The esophageal mucosa was denatured and had lost elasticity. Serum cholinesterase activity was 9 IU/L. Toxicological analyses performed using high-performance liquid chromatography-tandem mass spectrometry revealed that dichlorvos concentrations in the left and right cardiac blood samples were 11.6 and 4.6 µg/mL, respectively. Phenthoate concentrations in the left and right cardiac blood samples were 5.8 and 0.51 µg/mL, respectively. The total amounts of dichlorvos and phenthoate in the stomach were 7.35 and 4.55 g, respectively. The case history, autopsy findings, and toxicological analyses indicated that the cause of death was acute fatal poisoning after oral ingestion of both dichlorvos and phenthoate.

Bioscavenger is effective as a delayed therapeutic intervention following percutaneous VX poisoning in the guinea-pig.

The prolonged systemic exposure that follows skin contamination with low volatility nerve agents, such as VX, requires treatment to be given over a long time due to the relatively short half-lives of the therapeutic compounds used. Bioscavengers, such as butyrylcholinesterase (BChE), have been shown to provide effective post-exposure protection against percutaneous nerve agent when given immediately on signs of poisoning and to reduce reliance on additional treatments. In order to assess the benefits of administration of bioscavenger at later times, its effectiveness was assessed when administration was delayed for 2h after the appearance of signs of poisoning in guinea-pigs challenged with VX (4×LD50). VX-challenged animals received atropine, HI-6 and avizafone on signs of poisoning and 2h later the same combination with or without bioscavenger. Five out of 6 animals which received BChE 2h after the appearance of signs of poisoning survived to the end of the study at 48h, compared with 6 out of 6 which received BChE immediately on signs. All the animals (n=6+6) that received only MedCM, without the addition of BChE, died within 10h of poisoning. The toxicokinetics of a sub-lethal challenge of percutaneous VX were determined in untreated animals. Blood VX concentration peaked at approximately 4h after percutaneous dosing with 0.4×LD50; VX was still detectable at 36h and had declined to levels below the lower limit of quantification (10pg/mL) by 48h in 7 of 8 animals, with the remaining animal having a concentration of 12pg/mL. These studies confirm the persistent systemic exposure to nerve agent following percutaneous poisoning and demonstrate that bioscavenger can be an effective component of treatment even if its administration is delayed.

The efficacy of HI-6 DMS in a sustained infusion against percutaneous VX poisoning in the guinea-pig.

Post-exposure nerve agent treatment usually includes administration of an oxime, which acts to restore function of the enzyme acetylcholinesterase (AChE). For immediate treatment of military personnel, this is usually administered with an autoinjector device, or devices containing the oxime such as pralidoxime, atropine and diazepam. In addition to the autoinjector, it is likely that personnel exposed to nerve agents, particularly by the percutaneous route, will require further treatment at medical facilities. As such, there is a need to understand the relationship between dose rate, plasma concentration, reactivation of AChE activity and efficacy, to provide supporting evidence for oxime infusions in nerve agent poisoning. Here, it has been demonstrated that intravenous infusion of HI-6, in combination with atropine, is efficacious against a percutaneous VX challenge in the conscious male Dunkin-Hartley guinea-pig. Inclusion of HI-6, in addition to atropine in the treatment, improved survival when compared to atropine alone. Additionally, erythrocyte AChE activity following poisoning was found to be dose dependent, with an increased dose rate of HI-6 (0.48mg/kg/min) resulting in increased AChE activity. As far as we are aware, this is the first study to correlate the pharmacokinetic profile of HI-6 with both its pharmacodynamic action of reactivating nerve agent inhibited AChE and with its efficacy against a persistent nerve agent exposure challenge in the same conscious animal.

Fatal poisoning by terbufos following occupational exposure.

CONTEXT: Terbufos (TBF) is a class Ia (extremely hazardous) organophosphate pesticide (OP) and its distribution in industrialized countries has been severely restricted. Thus, acute occupational poisoning is rather uncommon. However, it still occurs in rural areas of some developing countries, where the sale of TBF is not controlled and its use is thus not properly regulated. We report a case of a 43-year-old female farmer who died after applying TBF granules. CASE: The patient died within 3 h after applying 20 bags of 5% TBF granules (900 g per bag). Investigation showed that her personal protective equipment (PPE) did not provide effective protection against dermal and inhalational exposure. Postmortem analysis revealed extremely low red blood cell acetylcholinesterase activity. Toxicological analysis of TBF showed 1.45 × 10-2 µg/ml in the heart blood and 0.17 µg/g in the liver. DISCUSSIONS: This patient died as a result of toxicity from dermal and inhalational exposure to TBF. Over-application, improper equipment, inadequate and defective PPE, and lack of hygienic precautions were all contributing factors. CONCLUSIONS: TBF is a highly toxic OP. Inadequate regulatory control, improper environmental application, and ineffective PPE resulted in a fatal human exposure.

Efficacy of novel phenoxyalkyl pyridinium oximes as brain-penetrating reactivators of cholinesterase inhibited by surrogates of sarin and VX.

Pyridinium oximes are strong nucleophiles and many are effective reactivators of organophosphate-inhibited cholinesterase (ChE). However, the current oxime reactivators are ineffective at crossing the blood-brain barrier and reactivating brain ChE in the intact organism. Our laboratories have developed a series of substituted phenoxyalkyl pyridinium oximes (US patent 9,227,937 B2) with the goal of identifying reactivators effective in crossing the blood-brain barrier. The first 35 of the series were found to have similar in vitro efficacy as reactivators of ChE inhibited by a sarin surrogate (phthalimidyl isopropyl methylphosphonate, PIMP) or a VX surrogate (nitrophenyl ethyl methylphosphonate, NEMP) in bovine brain preparations as previously observed in rat brain preparations. A number of these novel oximes have shown the ability to decrease the level of ChE inhibition in the brains of rats treated with a high sublethal dosage of either a sarin surrogate (nitrophenyl isopropyl methylphosphonate, NIMP) or the VX surrogate NEMP. Levels of reactivation at 2 h after oxime administration were up to 35% while the currently approved therapeutic, 2-PAM, yielded no reduction in brain ChE inhibition. In addition, there was evidence of attenuation of seizure-like behavior with several of the more effective novel oximes, but not 2-PAM. Therefore these novel oximes have demonstrated an ability to reactivate inhibited ChE in brain preparations from two species and in vivo data support their ability to enter the brain and provide a therapeutic action. These novel oximes have the potential to be developed into improved antidotes for nerve agent therapy.

The potential role of bioscavenger in the medical management of nerve-agent poisoned casualties.

The provision of effective Medical Countermeasures (MedCM) for all agents and routes of exposure is a strategic goal of defence research and development. In the case of military autoinjector-based therapies for nerve agent poisoning, current treatment effectiveness is limited by the oxime reactivator being effective against only certain agents, by rapid clearance times of the drugs and because the doses may not be optimal for treatment of severe poisoning. Prolonged poisoning by nerve agents entering the body through the skin is also challenging. Since casualty handling timelines have reduced significantly in recent years, it may be sufficient for first aid therapy to provide protection for only a few hours until further medical treatment is available. Therefore, the traditional evaluation of first aid therapy in animal models of survival at 24 h may not be appropriate. At various echelons of medical care, further therapeutic interventions are possible. The current basis for the medical management of nerve-agent poisoned casualties is derived mainly from clinical experience with pesticide poisoning. Adjunct therapy with a bioscavenger (such as human butyrylcholinesterase (huBChE)), could have utility as a delayed intervention by reducing the toxic load. It has previously been demonstrated that huBChE is an effective post-exposure therapy against percutaneous VX poisoning. It is recommended that the scope of animal models of nerve agent MedCM are extended to cover evaluation of both first aid MedCM over significantly reduced timescales, and subsequent supportive therapeutic and medical management strategies over longer timescales. In addition to bioscavengers, these strategies could include repeated combined and individual therapy drugs to alleviate symptoms, other classes of drugs or ventilatory support. Crown Copyright © [2016] Published by Elsevier Ireland Ltd. This is an open access article under the Open Government Licence (OGL) (http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/).

HI-6 assisted catalytic scavenging of VX by acetylcholinesterase choline binding site mutants.

The high toxicity of organophosphorus compounds originates from covalent inhibition of acetylcholinesterase (AChE), an essential enzyme in cholinergic neurotransmission. Poisonings that lead to life-threatening toxic manifestations require immediate treatment that combines administration of anticholinergic drugs and an aldoxime as a reactivator of AChE. An alternative approach to reduce the in vivo toxicity of OPs focuses on the use of bioscavengers against the parent organophosphate. Our previous research showed that AChE mutagenesis can enable aldoximes to substantially accelerate the reactivation of OP-enzyme conjugates, while dramatically slowing down rates of OP-conjugate dealkylation (aging). Herein, we demonstrate an efficient HI-6-assisted VX detoxification, both ex vivo in human blood and in vivo in mice by hAChE mutants modified at the choline binding site (Y337A and Y337A/F338A). The catalytic scavenging of VX in mice improved therapeutic outcomes preventing lethality and resulted in a delayed onset of toxicity symptoms.

[The influence of sodium bicarbonate combined with ulinastatin on cholinesterase activity for patients with acute phoxim pesticide poisoning].

OBJECTIVE: To observe the effect of sodium bicarbonate combined with ulinastatin on cholinesterase activity for patients with acute phoxim pesticide poisoning. METHODS: A total of 67 eligible patients with acute phoxim pesticide poisoning, Who were admitted to the emeryency department of hospital from March 2011 to February 2014, Acording to different treatments au patients were randomly divided into the conventional treatment group (n=34) and the sodium bicarbonate+ulinastatin group (n=35) . The conventional treatment group were given thorough gastric lavage with water, the sodium bicarbonate + ulinastatin group were given gastric lavage with 2% sodium bicarbonate solution. Both groups were given such treatments as catharsis, administration of oxygen, fluid infusion, diuresis, and antidotes such as atropine and pralidoxime methylchloride. On the basis of comprehensive treatment, people in the sodium bicarbonate+ulinastatin group were given 5% sodium bicarbonate injection and ulinastatin. The clinical effect of the two groups were compared. RESULTS: The serum cholinesterase activity of the sodium bicarbonate+ulinastatin group was significantly higher than the conventional treatment group from the 5th day, and the difference was statistically significant (P<0.05) . The total atropine dosage, total pralidoxime methylchloride dosage and hospitalization days were better than the conventional treatment group, and the differences were statistically significant (P<0.05) . The difference in the time of atropinization between the two groups was not statistically significant (P>0.05) . The results of arterial blood pH, HCO3- of the sodium bicarbonate + ulinastatin group were higher than the conventional treatment group, and the difference of HCO3- at the 10th day was statistically significant (P<0.05) . CONCLUSIONS: Sodium bicarbonate combined with ulinastatin can improve the therapeutic effect and reduce complications in the treatment of acute phoxim pesticide poisoning, and have beneficial effects on the recovery of cholinesterase activity.

Reversed-phase ion-pair chromatography-diode array detection of the bispyridinium compound MB327: plasma analysis of a potential novel antidote for the treatment of organophosphorus poisoning.

In the case of poisoning by organophosphorus nerve agents or pesticides, there is still a lack of pharmacological treatment of the cholinergic crisis selectively targeting the nicotinic acetylcholine receptor. Recently, the compound MB327 was identified as a potential novel lead structure to close this gap, thus demanding a quantitative assay for initial pharmacokinetic (PK) studies. MB327 is a salt consisting of the dicationic bispyridinium compound (BPC) 1,1´-(propane-1,3-diyl)bis(4-tert-butylpyridinium) and two iodide counter ions. Due to the permanent positive charge of the BPC, an isocratic reversed-phase ion-pair chromatographic separation (RPIPC) was developed using heptanesulfonic acid as ion-pairing reagent and 45% v/v methanol as organic modifier (1 mL/min). Selective UV-detection (230 nm) was done by a diode array detector (DAD) for reliable, rugged, precise (RSD < 7%) and accurate (96-104%) quantitative analysis of 50 µL swine plasma (linear range 1-1000 µg BPC/mL plasma, lower limit of quantification 2 µg/mL). During method validation, diverse parameters essential for the chromatographic process were investigated to generate van´t Hoff, van Deemter and width plots allowing calculation of thermodynamic data like the distribution constant K (5.7 ± 0.3), change in enthalpy, ΔH(0) : -23.66 kJ/mol, and entropy, ΔS(0) : -65 J/(mol*K). In addition, RPIPC-DAD analysis enabled calculation of molar absorptivities of the BPC, ε230 : 17 400 ± 1100 L/(mol*cm), and iodide, ε230 : 9900 ± 400 L/(mol*cm), which determination was hampered by interference with each other in conventional cuvette UV-spectrophotometric measurements. Finally, the RPIPC-DAD procedure was applied to samples from an in vivo study of swine.

Repetitive obidoxime treatment induced increase of red blood cell acetylcholinesterase activity even in a late phase of a severe methamidophos poisoning: A case report.

Accidental self-poisoning or deliberate use in suicidal intent of organophosphorus pesticides (OPP), which are widely used in agriculture, represent a health problem worldwide. Symptoms of poisoning are characterized by acute cholinergic crisis caused by inhibition of acetylcholinesterase. A 75-year-old male patient ingested 20ml of an OPP solution containing 10% methamidophos in suicidal intent. In the course of poisoning typical clinical symptoms of cholinergic crisis (miosis, bradycardia, hypotension, hypersalivation and impairment of neurologic status) were evident. Butyryl (plasma) cholinesterase (BChE) and red blood cell acetylcholinesterase (RBC-AChE) revealed decreased activities, thus specific treatment with the enzyme reactivator obidoxime was started. Inhibitory activity of the patient's plasma indicated significant amounts of persisting methamidophos in the circulation and was still found on day 4 after ingestion. Due to missing spontaneous breathing on day 6, obidoxime was administered again. Afterwards a significant increase of RBC-AChE activity was found. The patient was extubated on day 10 and a restitution ad integrum was achieved. In conclusion, obidoxime is a potent reactivator of OPP-inhibited AChE. A repetitive and prolonged administration of obidoxime should be considered in cases of severe methamidophos poisoning and should be tailored with an advanced analytical biomonitoring.