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Combinations of different drugs are formulated in autoinjectors for parenteral administration against neurotoxic war agents. In this work, the effects on the chemical stability of the following three variables were studied: (i) type of drug combination (pralidoxime, atropine, and midazolam versus obidoxime, atropine, and midazolam); (ii) pH (3 versus 4); and (iii) type of elastomeric sealing material (PH 701/50 C BLACK versus 4023/50 GRAY). Syringes were stored at three different temperatures: 4, 25, and 40 °C. Samples were assayed at different time points to study the physical appearance, drug sorption on the sealing elastomeric materials, and drug content in solution. Midazolam was unstable in all tested experimental conditions. Drug adsorption was observed in both types of sealing elastomeric materials and was significantly (p < 0.01) dependent on the lipophilicity of the drug. The most stable formulation was the combination of pralidoxime and atropine at pH 4 with the elastomeric sealing material 4023/50 GRAY. [ABSTRACT FROM AUTHOR]

Combinations of different drugs are formulated in autoinjectors for parenteral administration against neurotoxic war agents. In this work, the effects on the chemical stability of the following three variables were studied: (i) type of drug combination (pralidoxime, atropine, and midazolam versus obidoxime, atropine, and midazolam); (ii) pH (3 versus 4); and (iii) type of elastomeric sealing material (PH 701/50 C BLACK versus 4023/50 GRAY). Syringes were stored at three different temperatures: 4, 25, and 40 °C. Samples were assayed at different time points to study the physical appearance, drug sorption on the sealing elastomeric materials, and drug content in solution. Midazolam was unstable in all tested experimental conditions. Drug adsorption was observed in both types of sealing elastomeric materials and was significantly (p < 0.01) dependent on the lipophilicity of the drug. The most stable formulation was the combination of pralidoxime and atropine at pH 4 with the elastomeric sealing material 4023/50 GRAY.

A 63-year-old male was admitted to a district hospital after ingesting ethanol and pirimiphos-methyl (PM) with suicidal intentions. History included alcoholic cirrhosis with alcoholism, adiposity, diabetes with cerebral microangiopathy, chronic renal insufficiency, heparin-induced thrombocytopenia, and status post necrotizing fasciitis. Emergency medical service reported an alert patient without signs of cholinergic crisis; activated charcoal and atropine were administered. Upon hospital arrival, he received fluid resuscitation, activated charcoal, and atropine. He was transferred to a toxicology unit the next day. On admission, he had no cholinergic signs (dry mucous membranes, warm skin, and mydriatic pupils) requiring small atropine doses (0.5 mg per hour). Four hours after admission, he developed bradycardia and respiratory distress, necessitating intubation. He received atropine by continuous infusion for 7 days (248 mg total) and obidoxime (bolus and continuous infusion). PM, pirimiphos-methyl-oxon (PMO), and phosphorylated tyrosine (Tyr) adducts derived from human serum albumin were analyzed in vivo. Cholinesterase status (acetylcholinesterase (AChE), butyrylcholinesterase (BChE), inhibitory activity of patient plasma and reactivatability, and phosphorylated BChEderived nonapeptides) was measured in vivo. Obidoxime and atropine were monitored. PM and PMO were detectable, PM with maximum concentration ~24 h post admission (p.a.) and PMO at ~18 h p.a. Tyr adducts were detectable. AChE in vivo was suppressed on admission, increased continuously after starting obidoxime, and reached maximum activity after ~30 h. AChE in vivo and reactivatability remained at the same level until the end of monitoring. BChEwas already suppressed on admission; termination of the antidote treatment was possible after BChE had recovered to 1/5th of its normal value and extubation was possible after BChE had recovered to 2/5th. While a substantial part of BChE was already aged on admission, aging continued peaking at ~24 h p.a. After initiating obidoxime treatment, plasma levels increased until obidoxime plasma levels reached a steady state. On admission, plasma atropine level was low; it increased with the start of the continuous infusion. Afterward, the level dropped to a steady state. The clinical course was characterized by bouts of pneumonia, necessitating re-intubation and prolonged ventilation, sepsis, delirium, and a peripheral neuropathy. After psychiatric evaluation, the patient was discharged to a neurological rehabilitation facility after 77 days of hospital care. [ABSTRACT FROM AUTHOR]

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

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. [ABSTRACT FROM AUTHOR]

A 63-year-old male was admitted to a district hospital after ingesting ethanol and pirimiphos-methyl (PM) with suicidal intentions. History included alcoholic cirrhosis with alcoholism, adiposity, diabetes with cerebral microangiopathy, chronic renal insufficiency, heparin-induced thrombocytopenia, and status post necrotizing fasciitis. Emergency medical service reported an alert patient without signs of cholinergic crisis; activated charcoal and atropine were administered. Upon hospital arrival, he received fluid resuscitation, activated charcoal, and atropine. He was transferred to a toxicology unit the next day. On admission, he had no cholinergic signs (dry mucous membranes, warm skin, and mydriatic pupils) requiring small atropine doses (0.5 mg per hour). Four hours after admission, he developed bradycardia and respiratory distress, necessitating intubation. He received atropine by continuous infusion for 7 days (248 mg total) and obidoxime (bolus and continuous infusion). PM, pirimiphos-methyl-oxon (PMO), and phosphorylated tyrosine (Tyr) adducts derived from human serum albumin were analyzed in vivo. Cholinesterase status (acetylcholinesterase (AChE), butyrylcholinesterase (BChE), inhibitory activity of patient plasma and reactivatability, and phosphorylated BChE-derived nonapeptides) was measured in vivo. Obidoxime and atropine were monitored. PM and PMO were detectable, PM with maximum concentration ∼24 h post admission (p.a.) and PMO at ∼18 h p.a. Tyr adducts were detectable. AChE in vivo was suppressed on admission, increased continuously after starting obidoxime, and reached maximum activity after ∼30 h. AChE in vivo and reactivatability remained at the same level until the end of monitoring. BChE was already suppressed on admission; termination of the antidote treatment was possible after BChE had recovered to 1/5th of its normal value and extubation was possible after BChE had recovered to 2/5th. While a substantial part of BChE was already aged on admission, aging continued peaking at ∼24 h p.a. After initiating obidoxime treatment, plasma levels increased until obidoxime plasma levels reached a steady state. On admission, plasma atropine level was low; it increased with the start of the continuous infusion. Afterward, the level dropped to a steady state. The clinical course was characterized by bouts of pneumonia, necessitating re-intubation and prolonged ventilation, sepsis, delirium, and a peripheral neuropathy. After psychiatric evaluation, the patient was discharged to a neurological rehabilitation facility after 77 days of hospital care.

Cholinergic syndrome is a common topic at western medical universities yet rarely observed in clinical practice. The treatment involves muscarinic antagonists, acetylcholinesterase reactivation, seizure control, and supportive measures. Here we report a case of a 52-year old Caucasian male who attempted suicide by ingesting a purple crystal powder that turned out to be a mixture of carbofuran and chlormephos. At clinical examination, the patient presented with salivation, perspiration, diarrhoea, bradypnoea, loss of consciousness, and epileptic seizures. Laboratory tests showed low plasma cholinesterase, and we started obidoxime along with supportive intensive care treatment. He was later transferred to the psychiatry department for further diagnostics and treatment.

Mono- and bis-pyridinium quaternary aldoximes (K-oximes) have long been employed as cholinesterase reactivator components of antidotes against lethal cholinesterase-inhibiting organophosphorous chemicals. Their positive charge poses difficulties in their chromatographic analysis, resulting in the publication of different approaches for each K-oxime. A multiplexed method is presented for the rapid quantitation of 10 K-oximes in blood with its utility demonstrated in vivo. Liquid chromatography with absorbance detection was employed. Reversed-phase separation was achieved on a highly nonpolar stationary phase. Method validation was based on the respective guideline of the European Medicines Agency. Times to peak concentrations and 120-min areas under the time–concentration curves were determined in rats following intraperitoneal administration. Adequate retention and separation of K-oximes with acceptable peak shapes in short isocratic runs was achieved by adjusting ionic strength, organic content and the concentration of the ion-pairing agent of the mobile phase. Chromatographic properties were governed by optimizing the concentration of dissolved ions. Accurate adjustment of the organic content was indispensable for avoiding peak drifting and splitting. Dose-adjusted exposure to K-347 and K-868 was exceptionally low, while exposure to K-48 was the highest. The method is suitable for screening systemic exposure to various K-oximes and can be extended. [ABSTRACT FROM AUTHOR]

Effective intracerebral delivery acetylcholinesterase (AChE) reactivator is key for the acute organophosphorus (OPs) poison treatment. However, the blood-brain barrier (BBB) restricts the transport of these drugs from blood into the brain. Herein, we developed transferrin receptor (TfR) aptamer-functionalized liposomes (Apt-LP) that could deliver AChE reactivator (obidoxime) across the BBB to act against paraoxon (POX) poisoning. The aptamer had strong affinity for TfR and was modified with 3′-inverted deoxythymidine (dT) to improve serum stability. The uptake of Apt-LP by bEnd.3 cells was significantly higher than that of non-targeting liposomes. The ability of Apt-LP to penetrate intact BBB was confirmed in in vitro BBB mice model and in vivo biodistribution studies. Treatment of POX-poisoned mice with Apt-LP-LuH-6 reactivated 18% of the brain AChE activity and prevented brain damage to some extent. Taken together, these results showed that Apt-LP may be used as a promising brain-targeted drug delivery system against OPs toxicity. Unlabelled Image • Transferrin receptor aptamer-functionalized liposomes (Apt-LP) were developed. • Apt-LP could deliver AChE reactivator, obidoxime, across blood-brain barrier. • Apt-LP could effectively transport obidoxime across the BBB model in vitro. • Apt-LP exhibited a satisfactory efficiency in brain delivery. • Apt-LP may be used against organophosphorus poisoning. [ABSTRACT FROM AUTHOR]

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

• Nerve agents (NA) inhibit the enzyme acetylcholinesterase (AChE). • This inhibition causes NA-induced brain damage in central nervous system. • Oximes reactivates AChE in both the peripheral and the central nervous system. • Oximes could not cross the blood–brain barrier (BBB) in therapeutic concentrations. • Loading obidoxime to PLGA and PEG-b-PLGA nanoparticles improved the BBB transport of the oximes. Nerve agents (NA) are chemical warfare munitions and their exposure causes a progressive inhibition of acetylcholinesterase (AChE). This inhibition causes NA-induced brain damage in central nervous system (CNS). Oximes reactivate AChE in both the peripheral nervous system and the CNS. Transport of the oxime across the blood–brain barrier (BBB) in the existed therapeutic concentrations at the brain parenchyma determines the effectiveness of antidote therapy on respiratory depression and NA-induced brain damage. However, oximes could not cross the BBB in therapeutic concentrations. The aim of this study was to load AChE reactivator obidoxime chloride to PLGA and PEG-b-PLGA nanoparticles and to improve the BBB transport of the molecule. Brain microvascular endothelial cells were used as the BBB model. 79.3 ± 4.2% of obidoxime was released from PLGA nanoparticles and 88.2 ± 4.4% of obidoxime was released from PEG-b-PLGA nanoparticles within 24 h. It was found that PEG-b-PLGA nanoparticles were ideal drug carrier because of its low tissue toxicity, few side effects, and controllable drug release profile. Transport efficiency of obidoxime across the BBB is a major challenge in the prevention of the CNS, the effectiveness of NA poisoning and new strategies like using obidoxime-loaded PEG-b-PLGA nanoparticles could overcome this challenge for the management of NA-induced brain damage. [ABSTRACT FROM AUTHOR]

Cholinergic syndrome is a common topic at western medical universities yet rarely observed in clinical practice. The treatment involves muscarinic antagonists, acetylcholinesterase reactivation, seizure control, and supportive measures. Here we report a case of a 52-year old Caucasian male who attempted suicide by ingesting a purple crystal powder that turned out to be a mixture of carbofuran and chlormephos. At clinical examination, the patient presented with salivation, perspiration, diarrhoea, bradypnoea, loss of consciousness, and epileptic seizures. Laboratory tests showed low plasma cholinesterase, and we started obidoxime along with supportive intensive care treatment. He was later transferred to the psychiatry department for further diagnostics and treatment. [ABSTRACT FROM AUTHOR]

• PK of three oximes was determined in healthy and sarin-challenged guinea pigs. • Combination of oxime therapy does not result in adverse events. • PK of each oxime is not affected by combined administration or GB exposure. • Combined oxime use shows similar efficacy to a double dose of a single oxime. Organophosphorus nerve agents (NA) inhibit acetylcholinesterase (AChE) which results in the over-stimulation of both the central and peripheral nervous systems, creating a toxic syndrome that can be lethal if left untreated (Cannard, 2006). It is standard practice to treat Sarin (GB) intoxication with an oxime, an antimuscarinic such as atropine and an anticonvulsant. Three common oximes are available: HI-6, Pralidoxime (2-PAM) and Obidoxime (Obi), all possess a nucleophile that can break the NA-AChE covalent bond. However, each oxime's efficacy profile against various agents is different (Thiermann and Worek, 2018). In an effort to broaden therapeutic efficacy against a range of possible NA's, consideration should be given to the use of two oximes in combination. Using a guinea pig model, the first arm of this study was to determine the pharmacokinetics (PK) of HI-6 DMS, 2-PAM chloride and Obi chloride (at autoinjector equivalent doses) following intramuscular (i.m.) co-administration along with atropine to replicate either a single isometrically scaled dose (referred to in this study as a single autoinjector equivalent) of 2-PAM (and equimolar doses of Obi and HI-6) or double doses (referred to in this study as two autoinjector equivalents). The second arm of the study evaluated the efficacy of Obi and 2-PAM individually at a single or double autoinjector dose and also in combination against GB exposure. Pharmacokinetic profiles of each oxime were evaluated for both arms of the study and no significant change in parameters were reported. Improved cholinesterase reactivation was observed in a dose dependent manner with combined therapy showing similar reactivation to individual oximes alone at a two autoinjector equivalent dose. Seizure activity was reduced when combined oxime therapy was administered. This improvement was also reflected in the Racine seizure index score assigned at the end of the experimental period. To the best of our knowledge, this study is the first to evaluate and compare the pharmacokinetics of three oximes and the combination of two oximes (2-PAM and Obi) administered in naïve animals or those exposed to GB. Combined oxime therapy (Obi and 2-PAM) resulted in improved seizure control, increased cholinesterase reactivation peripherally and centrally and improved behavioral signs (Racine score). This study provides evidence that combination of oximes is effective, does not result in adverse events and that the pharmacokinetics of each oxime are not affected when administered in combination. [ABSTRACT FROM AUTHOR]

Poisoning with organophosphorus compounds (OPCs) is a major problem worldwide. Standard therapy with atropine and established oxime-type enzyme reactivators (pralidoxime, obidoxime) is unsatisfactory. In search of more efficacious broad-spectrum oximes, new bispyridinium (K-) oximes have been synthesized, with K027 being among the most promising. This review summarizes pharmacokinetic characteristics of K027, its toxicity and in vivo efficacy to protect from OPC toxicity and compares this oxime with another experimental bisquaternary asymmetric pyridinium aldoxime (K048) and two established oximes (pralidoxime, obidoxime). After intramuscular (i.m.) injection, K027 reaches maximum plasma concentration within ∼30 min; only ∼2% enter the brain. Its intrinsic cholinesterase inhibitory activity is low, making it relatively non-toxic. In vitro reactivation potency is high for ethyl-paraoxon-, methyl-paraoxon-, dichlorvos-, diisopropylfluorophosphate (DFP)- and tabun-inhibited cholinesterase. When administered in vivo after exposure to the same OPCs, K027 is comparable or more efficacious than pralidoxime and obidoxime. When given as a pretreatment before exposure to ethyl-paraoxon, methyl-paraoxon, DFP, or azinphos-methyl, it is superior to the Food and Drug Administration-approved compound pyridostigmine and comparable to physostigmine, which because of its entry into the brain may cause unwanted behavioral effects. Because of its low toxicity, K027 can be given in high dosages, making it a very efficacious oxime not only for postexposure treatment but also for prophylactic administration, especially when brain penetration is undesirable.

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

Poisoning with organophosphorus compounds (OPCs) is a major problem worldwide. Standard therapy with atropine and established oxime-type enzyme reactivators (pralidoxime, obidoxime) is unsatisfactory. In search of more efficacious broad-spectrum oximes, new bispyridinium (K-) oximes have been synthesized, with K027 being among the most promising. This review summarizes pharmacokinetic characteristics of K027, its toxicity and in vivo efficacy to protect from OPC toxicity and compares this oxime with another experimental bisquaternary asymmetric pyridinium aldoxime (K048) and two established oximes (pralidoxime, obidoxime). After intramuscular (i.m.) injection, K027 reaches maximum plasma concentration within ∼30 min; only ∼2% enter the brain. Its intrinsic cholinesterase inhibitory activity is low, making it relatively non-toxic. In vitro reactivation potency is high for ethyl-paraoxon-, methyl-paraoxon-, dichlorvos-, diisopropylfluorophosphate (DFP)- and tabun-inhibited cholinesterase. When administered in vivo after exposure to the same OPCs, K027 is comparable or more efficacious than pralidoxime and obidoxime. When given as a pretreatment before exposure to ethyl-paraoxon, methyl-paraoxon, DFP, or azinphos-methyl, it is superior to the Food and Drug Administration-approved compound pyridostigmine and comparable to physostigmine, which because of its entry into the brain may cause unwanted behavioral effects. Because of its low toxicity, K027 can be given in high dosages, making it a very efficacious oxime not only for postexposure treatment but also for prophylactic administration, especially when brain penetration is undesirable. [ABSTRACT FROM AUTHOR]

Abstract The efficacy and pharmacokinetics of the aqueous co-formulation contents of the Trobigard™ (atropine sulfate, obidoxime chloride) auto-injector were evaluated in a sarin exposed guinea pig model. Two subcutaneous (sc) sarin challenge doses were evaluated in guinea pigs instrumented with brain and heart electrodes for electroencephalogram (EEG) and electrocardiogram (ECG). Sarin challenge doses were chosen to reflect exposure subclasses with sublethal (moderate to severe clinical signs) and lethal consequences. The level of protection of intramuscular human equivalent doses of the co-formulation was defined by (1) the mitigation of signs and symptoms at a sublethal level and (2) the increase of survival time at the supralethal sarin dose levels. Pharmacokinetics of both atropine sulfate and obidoxime were proportional at 1 and 3 human equivalent doses, and only a small increase in heart rate was observed briefly as a side effect. At both sarin challenge doses, 54 μg/kg and 84 μg/kg, the co-formulation treatment was effective against sarin-induced effects. Survival rates were improved at both sarin challenge levels, whereas clinical signs and changes in EEG activity could not in all cases be effectively mitigated, in particular at the supralethal sarin challenge dose level. Reactivation of sarin inhibited cholinesterase was observed in blood, and higher brain cholinesterase activity levels were associated with a better clinical condition of the co-formulation treated animals. Although the results cannot be directly extrapolated to the human situation, pharmacokinetics and the effects over time related to plasma levels of therapeutics in a freely moving guinea pig could aid translational models and possibly improve prediction of efficacy in humans. Highlights • Atropine/obidoxime pharmacokinetics were dose proportional and not affected by Sarin challenge. • Survival rates were improved by atropine/obidoxime at two sarin challenge levels. • Reactivation of sarin inhibited cholinesterase was observed in blood. • Effective mitigation of CNS effects was only apparent at the lower sarin challenge. • The primary benefit is a gain in time to allow for supportive treatment. [ABSTRACT FROM AUTHOR]

Obidoxime is a pharmacologically active compound used as an acetylcholinesterase reactivator. The scope of this study was to establish correlations between its acid-base and redox equilibria and its mechanism as an acetylcholinesterase reactivator. The obidoxime dicationic structure is modified by the pH of the solvating medium due to tautomeric isomerizations. The possibility of stabilizing its structure as a dicationic, monocationic, and a neutral species was studied by ultraviolet-visible spectrometry and cyclic and differential pulse voltammetry. Spectrometric and voltammetric studies were performed across a large pH interval (2.00-9.80) of the solvating medium. Absorption measurements revealed the existence of three species involved in two tautomeric equilibria implying oxime and nitroso groups. The structure bearing nitroso groups, stabilized at higher pH, is more likely to behave as a nucleophilic agent than the structure with oxime groups, explaining thus its acetylcholinesterase reactivation. The obidoxime voltammetric behavior at a glassy carbon electrode is complex. Both its oxidation and reduction are diffusion-controlled processes. Anodic signals were obtained only at pH values above 6.50 and the oxidation occurs at the anion oxime group involving two electrons and one proton. The obidoxime reduction is pH dependent only for neutral or alkaline media, giving rise to two or even four signals (for pH higher than 7.50) depending on pH. The peak at less positive potentials was always well defined. [ABSTRACT FROM AUTHOR]

The ability of newly developed oximes (K347, K628) to reduce tabun-induced acute neurotoxic signs and symptoms was compared with currently available oximes (obidoxime, HI-6) using a functional observational battery. The neuroprotective effects of the oximes studied (K347, K628, obidoxime, HI-6) combined with atropine on rats poisoned with tabun at a sublethal dose (220 μg/kg i.m.; 80 % of LD50 value) were evaluated. Tabun-induced neurotoxicity was monitored by a functional observational battery and automatic measurement of motor activity at 24 hours following tabun challenge. The results indicate that all tested oximes combined with atropine enable tabun-poisoned rats to survive 24 hours following tabun challenge. Both newly developed oximes (K347, K628) combined with atropine are able to decrease tabun-induced neurotoxicity in the case of sublethal poisonings but they do not eliminate all tabun-induced acute neurotoxic signs and symptoms. Their ability to decrease the tabun-induced acute neurotoxicity is higher than that of the oxime HI-6 and it is slightly slower than the neuroprotective efficacy of obidoxime. As the neuroprotective potency of both newly developed oximes (K347, K628) is not as high as the potency of obidoxime, they are not a suitable replacement for obidoxime for the treatment of acute tabun poisonings.

The neuroprotective effects of newly developed oximes (K156, K203) and currently available oximes (obidoxime, HI-6) in combination with atropine in rats poisoned with cyclosarin were studied. The cyclosarin-induced neurotoxicity was monitored using a functional observational battery 24 hours after cyclosarin challenge. The results indicate that a newly developed oxime K156 is able to counteract slightly cyclosarin-induced neurotoxicity while another newly developed oxime K203 is completely ineffective in reducing cyclosarin-induced neurotoxic signs and symptoms. The neuroprotective efficacy of K156 is comparable with commonly used obidoxime and oxime HI-6. Thus, none of the newly developed oximes achieves better neuroprotective efficacy than both commonly used oximes. They are therefore not suitable replacements for antidotal treatment of acute poisonings with cyclosarin.

One-dimensional Pd–Au nanowires (Pd–Au NWs) were prepared and applied to fabricate an electrochemiluminescence (ECL) biosensor for the detection of acetylcholinesterase (AChE) activity. Compared with single-component of Pd or Au, the bimetallic nanocomposite of Pd–Au NWs offers a larger surface area for the immobilization of enzyme, and displays superior electrocatalytic activity and efficient electron transport capacity. In the presence of AChE and choline oxidase (ChOx), acetylcholine (ATCl) is hydrolyzed by AChE to generate thiocholine, then thiocholine is catalyzed by ChOx to produce H 2 O 2 in situ , which serves as the coreactant to effectively enhance the ECL intensity in luminol-ECL system. The detection principle is based on the inhibited AChE and reactivated AChE as dual biomarkers, in which AChE was inhibited by organophosphorus (OP) agents, and then reactivated by obidoxime. Such dual biomarkers method can achieve credible evaluation for AChE activity via providing AChE activity before and after reactivation. The liner range for AChE activity detection was from 0.025 U L −1 to 25 KU L −1 with a low detection limit down to 0.0083 U L −1 . [ABSTRACT FROM AUTHOR]

In the past, scientists focused on the development of antidotes (mainly anticholinergics in combination with reactivators of inhibited acetylcholinesterase – oximes) to increase the number of surviving nerve agent-intoxicated individuals. Recently, they are interested in antidotes able not only to protect nerve agent-poisoned men from lethal toxic effects but also to improve their life quality by improvement of their central cognitive functions. In our study, the water maze was used to measure spatial working learning and memory in the case of tabun-induced cognitive impairment in albino Wistar rats. Antidotal treatment consisted of atropine alone or a combination of atropine with an oxime (obidoxime, trimedoxime or oxime HI-6). Our results suggest that atropine alone is not sufficient as a treatment for saving cognitive functions impaired by tabun. On the other hand, the addition of oxime to atropine contributes to improvement of cognitive performance in tabun-poisoned rats regardless of type of oxime.

1. The efficacy of the oxime HLö-7 and currently used oximes (pralidoxime, obidoxime, HI-6) to reactivate acetylcholinesterase inhibited by various nerve agents (sarin, tabun, cyclosarin, VX) was tested by in vitro methods. 2. Both H oximes (HLö-7, HI-6) were found to be more efficacious reactivators of sarin and VX-inhibited acetylcholinesterase than pralidoxime and obidoxime. On the other hand, their potency to reactivate tabun-inhibited acetylcholinesterase is very low and does not reach the reactivating efficacy of obidoxime. In the case of cyclosarin, the oxime HI-6 was only found to be able to sufficiently reactivate cyclosarin-inhibited acetylcholinesterase in vitro. 3. Thus, the oxime HLö-7 does not seem to be more efficacious reactivator of nerve agent-inhibited acetylcholinesterase than HI-6 according to in vitro evaluation of their reactivation potency and, therefore, it is not more suitable to be introduced for antidotal treatment of nerve agent-exposed people than HI-6.

Summary: 1. The influence of the time of administration of antidotal treatment consisting of anticholinergic drug (atropine) and oxime (pralidoxime, obidoxime, HI-6 or trimedoxime) on its effectiveness to eliminate tabun-induced lethal effects was studied in mice. 2. The therapeutic efficacy of antidotal treatment of tabun-induced acute poisoning depends on the time of its administration when obidoxime or the oxime HI-6 was used as an acetylcholinesterase reactivator. 3. Pralidoxime is practically ineffective to eliminate acute toxic effects of tabun regardless of the time of its administration. 4. Our results show that trimedoxime seems to be the most effective to eliminate lethal effects of tabun. In addition, its efficacy does not decrease when it is administered 5 min after tabun poisoning. 5. The findings support the hypothesis that trimedoxime appears to be the most suitable oxime to counteract acute toxicity of tabun because of its ability to eliminate lethal effects of tabun when it is injected 5 min after tabun challenge on the contrary to other oximes tested.

1. The influence of some acetylcholinesterase reactivators (HI-6, obidoxime, pralidoxime) on the efficacy of antidotal treatment to eliminate soman-induced disturbance of respiration and circulation and to protect experimental animals poisoned with supralethal dose of soman (1.5 × LD50) was investigated in a rat model with on-line monitoring of respiratory and circulatory parameters. 2. Obidoxime or pralidoxime in combination with atropine were insufficient to enable soman-poisoned rats to survive for 2 hours when given 1 minute after the administration of soman. 3. On the other hand, the ability of the oxime HI-6 in combination with atropine to prevent soman-induced alteration of respiration and circulation was significantly higher. Some rats treated with HI-6 in combination with atropine were fully protected against the lethal toxic effects of soman within 2 hours following soman administration. 4. Our findings confirm that the oxime HI-6 seems to be a much more suitable and efficacious acetylcholinesterase reactivator for the antidotal treatment of severe acute soman-induced poisoning than currently used obidoxime or pralidoxime.

A treatment regimen consisting of HI-6, levetiracetam, and procyclidine (termed the triple regimen) has previously been shown to work as a universal therapy against soman poisoning in rats, since it has capacities to function as both prophylactic and therapeutic measure. The purpose of the present study was to examine whether the triple regimen may have antidotal efficacy against intoxication by other classical nerve agents than soman. The treatment was given 1 and 5 min after exposure to a supralethal dose of nerve agents, and the results showed that the triple regimen successfully prevented or terminated seizures and preserved the lives of rats exposed to 5 × LD 50 of soman, sarin, cyclosarin, or VX, but solely 3 × LD 50 of tabun was managed by this regimen. To meet the particular antidotal requirements of tabun, the triple regimen was reinforced with obidoxime and was made to a quadruple regimen that effectively treated rats intoxicated by 5 × LD 50 of tabun. The rats recovered very well and the majority gained pre-exposure body weight within 7 days. Neuropathology was seen in all groups regardless of whether the rats seized or not. The most extensive damage was produced by sarin and cyclosarin. Differentiation between the nerve agents’ potency to cause lesions was probably seen because the efficacious treatments ensured survival of supralethal poisoning. A combination of 2 oximes and 2 anticonvulsants may be a prerequisite to counteract effectively high levels of poisoning by any classical nerve agent. [ABSTRACT FROM AUTHOR]

Pyridinium oxime-based drugs are generally used in the treatment of acute organophosphorus (OP) nerve agent poisoning. In this regard, a series of mono-pyridinium oximes bearing substituted phenacyl moieties as side chain were synthesized and screened for their in vitro reactivation efficacies against electric eel acetylcholinesterase (AChE) inhibited by OP inhibitors such as DFP, sarin and VX. The results of the in vitro reactivation data of the synthesized compounds were compared to standard antidotes 2-PAM and obidoxime. Among the synthesized compounds, 1a, 2a, 7a, 8a, 11a, 12a, 13a, 14a and 16a have shown better reactivation efficacy than 2-PAM and obidoxime against VX-inhibited AChE. Oximes 8a, 8b, 11a and 12a were at par with obidoxime in the reactivation of sarin-inhibited AChE. The pKa values for all the oximes were determined and correlated with their observed reactivation potential. [ABSTRACT FROM AUTHOR]

Eye exposure to the extremely toxic organophosphorus sarin results in long-term miosis and visual impairment. As current treatment using atropine or homatropine eye drops may lead to considerable visual side effects, alternative combined treatments of intramuscular (im) oximes (16.8 mmol/kg, im) with atropine (0.5 mg/kg, im) or with the short acting antimuscarinic tropicamide (0.5%; w/v) eye drops were thus evaluated. The combined treatments efficacy following topical exposure to sarin (1 mg) was assessed by measuring pupil width and light reflex using an infra-red based digital photographic system. Results showed that the combined treatment of various oximes with atropine or with topical tropicamide eye drops rapidly reversed the sarin-induced miosis and presented a long-termimprovement of 67-98% (oximeþtropicamide) or 84-109% (oximeþatropine) in pupil widening as early as 10-min following treatment. This recovery was shown to persist for at least 8-h following exposure. All combined treatments facilitated the ability of the iris to contract following sarin insult as tested by a light reflex response. Our findings emphasize the high efficacy of im oxime treatment combined with either atropine im or tropicamide eye drops in counteracting sarin-induced ocular insult. Therefore, in a mass casualty scenario the systemic combined treatment may be sufficient to ameliorate sarin-induced ocular insult with no need for additional, topical anticholinergic treatment at least in the initial stage of intoxication. For very mild casualties, who are unlikely to receive im treatment, the combined oxime (im) with topical tropicamide treatment may be sufficient in ameliorating the ocular insult. [ABSTRACT FROM AUTHOR]

1. The neuroprotective effects of antidotes (atropine, obidoxime/atropine mixture, HI-6/atropine mixture) on rats poisoned with soman at a sublethal dose (48 μg/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 24h and 7d 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.

Organophosphorus compounds are known to inhibit the esteratic site of acetylcholinesterase by phosphorylation. The phosphorylated esteratic site of acetylcholinesterase undergoes hydrolytic regeneration at a slow or negligible rate. Nucleophilic agents such as hydroxytamine, hydroxamic acids, and oximes reactivate the enzyme more erapidfy than does spontaneous hydrolysis. The red cell cholinesterose activity was assayed using dithio bis-2-nitrobenzoic acid (DTNB) commonly known as Ellman's reagent. The principle of this assay method is the rate of hydrolysis of acetylthiocholine (substrate) by a red celt suspension. Thiocholine that is produced, forms a yellow complex, when EUman's reagent (DTNB) is used in the assay. This was tested in vitro in lysed erythrocyte samples of 35 healthy persons who had no known exposure to cholinesterose inhibitors, after the observation of immediate increase in absorption of light at 440 nm. All of data were statistically analyzed using one-way ANOVA and student t-test. A value of p

The toxicity of cyclohexyl methylphosphonofluoridate (GF-agent; cyclosarin) and therapeutic efficacy of four oximes (trimedoxime, methoxime, obidoxime and HI-6) in combination with atropine or benactyzine (BNZ) was studied in mice. The oxime therapy combined with anticholinergic drug was administered intramusculary (i.m.) 1 or 2 min after i.m. GF-agent challenge. All the drugs were applied in dose of 20% of LD50. Obidoxime and trimedoxime that were combined with atropine were less effective than methoxime and HI-6 in combination with BNZ when applied 2 minutes after GF-agent poisoning. When the drugs were administered 1 min after GF-agent challenge already, in case of methoxime, the faster application of therapy resulted in significantly higher protective ratio, while for obidoxime the therapeutic effectivity did not depend significantly on the seasonableness of therapeutic intervention. The present findings show that all four combinations of oxime with anticholinergic drug decrease the GF-agent toxicity more than twofold regardless of the time of treatment administration.

The ability of two novel oximes K378 and K348 and currently available oximes (HI-6, obidoxime) to reactivate sarin-inhibited acetylcholinesterase and to reduce acute toxicity of sarin was evaluated. Both new potential oxime reactivators were chosen for this study based on the data obtained during the extensive work on oximes development, from structure–activity relationship studies and in vitro evaluation of their ability to reactivate acetylcholinesterase inhibited by organophosphorus compounds. In vivo determined percentage of reactivation of sarin-inhibited rat blood and brain acetylcholinesterase showed that the potency of both novel oximes K378 and K458 to reactivate sarin-inhibited acetylcholinesterase roughly corresponds to low reactivating efficacy of obidoxime. On the other hand, the oxime HI-6 was found to be efficient reactivator of sarin-inhibited acetylcholinesterase in the peripheral compartment. While the oxime HI-6 was able to reduce the acute toxicity of sarin more than three times, both novel oximes decreased the acute toxicity of sarin less than two times. Based on the results, we can conclude that reactivating and therapeutic efficacy of both novel oximes K378 and K458 are significantly lower compared to the oxime HI-6 and, therefore, it is not suitable to replace the oxime HI-6 for the antidotal treatment of acute sarin poisoning. [ABSTRACT FROM AUTHOR]

Background and Purpose Eye exposure to the organophosphorus ( OP) irreversible cholinesterase inhibitor sarin results in long-term miosis and impaired visual function. We have previously shown that tropicamide is better at ameliorating this insult than topical atropine or cyclopentolate. However, to minimize side effects associated with repeated tropicamide applications and high treatment doses, we evaluated the effects of oximes (ChE re-activators) alone and combined with tropicamide at ameliorating OP-induced ocular impairments. Experimental approach Rats were topically exposed to sarin, followed by topical treatment with various oximes alone or in combination with tropicamide. Pupil width and light reflex were measured by an infrared-based digital photograph system, while visual performance was assessed by employing the cueing version of the Morris water maze ( MWM). Key Results Oxime treatment following sarin ocular exposure induced a slow persistent pupil widening with efficacy in the order of HLö-7 > HI-6 > obidoxime = TMB-4 = MMB-4. In the light reflex test, the ability of the iris to contract following oxime treatment was mostly impaired at 1 h and was back to normal at 4 h following sarin exposure. All oxime treatments ameliorated the sarin-induced visual impairment as tested in the visual task ( MWM). The combined topical treatment of tropicamide with an oxime induced a rapid improvement in pupil widening, light reflex and visual performance, and enabled a reduction in tropicamide dose. Conclusions and Implications The use of tropicamide combined with an oxime should be considered as the topical treatment of choice against the toxic effects of ocular OP exposure. [ABSTRACT FROM AUTHOR]

Acetylcholinesterase reactivators (oximes) are highly hydrophilic compounds. This factor is considered to limit their distribution through the human body, especially into the central nervous system. However, some results contradict this hypothesis and confirm low concentrations of oximes inside the CNS. This study aims to verify oxime penetration through the blood-brain barrier, and into different brain regions. It has been confirmed that oximes can penetrate the BBB after therapeutic dose administration (0.73%, 0.69%, and 0.52% corresponding to obidoxime, HI-6, and new oxime K027). Although the whole brain level of K027 seems to be lower compared with other oximes we have to keep in mind that these numbers represent only a percentage of the concentration found in plasma. So, for more adequate comparison it is essential to have a look at the actual concentration of oximes in the wet brain tissue: 106.6 ± 19.87 ng/g (K027), 49.88 ± 10.21 ng/g (obidoxime) and 86.51 ± 42.37 ng/g (HI-6), where concentration of K027 was one order of magnitude higher than obidoxime and HI-6. In spite of the fact that the distribution of oximes into the CNS is minimal and concentrations differ from section to section, reasonable reactivation should still occur. [ABSTRACT FROM AUTHOR]

The potency of a novel oxime K203 in reactivating soman-inhibited acetylcholinesterase and reducing acute toxicity of soman was compared with commonly used oximes (HI-6, obidoxime, trimedoxime, methoxime) using in vivo methods. The study determining percentage of reactivation of soman-inhibited blood and tissue acetylcholinesterase in rats showed that the potency of the oxime K203 to reactivate soman-inhibited acetycholinesterase in the peripheral compartment is slightly higher than obidoxime and trimedoxime, especially in the diaphragm, slightly lower than methoxime and markedly lower compared to the oxime HI-6. The reactivating efficacy of the oximes studied in the peripheral compartment roughly corresponds to their potency to reduce acute toxicity of soman in mice. Based on the obtained data, we can conclude that the oxime K203 is not suitable for the replacement of the oxime HI-6 for the antidotal treatment of acute soman poisoning due to its relatively low potency to counteract acute toxicity of soman. [ABSTRACT FROM AUTHOR]

Atropine (AT) and oximes, alone or in combination, have been proven greatly valuable therapeutics in the treatment of organophosphates intoxications. An injectable mixture of AT and obidoxime (OB) was formulated for the administration by automatic self-injector. The aqueous single dose solution contained 275 mg obidoxime chloride and 2.5 mg atropine sulfate per 1 mL (220 mg and 2 mg per 0.8 effective dose, respectively). The final solution was sterilized by filtration through a 0.22 μm pore size filter. This more concentrated solution allowed to use a smaller size and lighter weight cartridge. Quality control tests, including assay of the two major compounds were performed separately, using reversed-phase HPLC methods. Besides, the stability test was carried out according to ICH guideline for the accelerated test. The obtained results showed that the proposed formulation is stable over a period of 2 years after preparation. [ABSTRACT FROM AUTHOR]

1. The therapeutic efficacy of various oximes (pralidoxime, obidoxime, methoxime, HI-6, HLö-7, BI-6) against supralethal nerve agent poisoning (soman, sarin, cyclosin) in mice was tested. 2. New oxime BI-6, synthesized in our laboratory, is significantly more efficacious than conventional oximes but a little less efficacious than other H-oximes (HI- 6, HLö-7). 3. H-oximes (HI-6, HLö-7) seem to be the most efficacious reactivators of nerve agent-inhibited acetylcholinesterase for antidotal treatment of supralethal nerve agent poisoning in mice.

Abstract: This communication describes synthesis and in vitro evaluation of a series of novel bis-pyridinium oximes connected by bis-methoxymethyl benzene, 1,4-bis-methoxymethyl (cis)-but-2-ene and 1,4-bis-methoxymethyl but-2-yne linkers as reactivators of sarin inhibited acetylcholinesterase (AChE). The reactivation data of synthesized oximes were compared with those of 2-PAM and obidoxime. The efficacy of oximes such as 1,4-dimethoxy cis-but-2-ene bis-[4,4′-(hydroxyiminomethyl)-pyridinium] dichloride (3g), 1,4-dimethoxy benzene bis-[3,3′-(hydroxyimino-methyl) pyridinium] dichloride (3b) and 1,3-dimethoxy benzene bis-[3,3′-(hydroxy-iminomethyl) pyridinium] dichloride (3e) were found to be more than that of obidoxime in reactivating sarin inhibited AChE. The oxime 3g was able to reactivate 25% of AChE activity in comparison to 20% and 5% reactivation exhibited by 2-PAM and obidoxime respectively at a concentration of 10−4 M. The pKa of the oximes were determined and correlated with the reactivation potential. [Copyright &y& Elsevier]

This study compares the abilities of the newly developed bispyridinium oxime K203 with currently available oximes (HI-6, obidoxime, and trimedoxime) in the reactivation of sarin-inhibited acetylcholinesterase and the reduction of the acute toxicity of sarin. The percentage of reactivation of sarin-inhibited rat blood and tissue acetylcholinesterase was determined in vivo and it was shown that the potency of bispyridinium oxime K203 to reactivate sarin-inhibited acetylcholinesterase roughly corresponds to the relatively low reactivating efficacy of obidoxime and trimedoxime except in the diaphragm where K203 was not effective. On the other hand, the oxime HI-6 was found to be a very efficient reactivator of sarin-inhibited acetylcholinesterase in the peripheral as well as central compartment. The oxime HI-6 was able to reduce the acute toxicity of sarin by more than four times, but the other oximes studied, including K203, decreased the acute toxicity of sarin by less than three times. Based on these results, we can conclude that the reactivating and therapeutic efficacy of the oxime K203 is significantly lower compared to the oxime HI-6 and, therefore, it is not a suitable replacement for the oxime HI-6 in the antidotal treatment of acute sarin poisoning. [ABSTRACT FROM AUTHOR]

Abstract: Victims of nerve agents basically require antidotal treatment. There is need for novel antidotes and for therapeutic procedures that are specifically adapted to these patients. To cope with this challenge, in vitro test systems which are easy to handle and allow for conducting long-term studies would be of great benefit. The present work introduces co-cultures of spinal cord and muscle tissue as ex vivo testing systems meeting these criteria. Cell cultures in which functional neuromuscular synapses formed ex vivo were prepared from embryonic mice. Spontaneous muscle activity was recorded by video microscopy. Muscle contractions involved intact neuromuscular transmission as indicated by the effect of succinylcholine, a muscle relaxant that completely abolished muscle activity. At a concentration of 0.75μM the nerve agent VX reduced the frequency of spontaneous muscle contractions by about 75%. Subsequent application of obidoxime re-established muscle movements. After 24h of antidotal treatment, muscle activity approached the level of sham-treated cultures and remained stable over the following week. In summary, co-cultures of spinal cord and muscle tissue are promising tools for evaluating the success of antidotal treatment following organophosphate intoxication over a period of at least seven days. [Copyright &y& Elsevier]

Oxime reactivator HI-6 (asoxime, in some sources) is a potent antidote suitable for treatment of intoxication by nerve agents. Despite the fact that HI-6 is considered for practical application in emergency situations, the impact of HI-6 on patients'' bodies has not been established yet. The present experiment was carried out in order to estimate whether HI-6 would be able to trigger or protect from oxidative stress in a BALB/c mice model. HI-6 was applied in doses ranging from 0.2 to 20% of LD50. Ferric-reducing antioxidant power (FRAP), thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH), and glutathione reductase (GR) were assayed in the blood, liver, kidney, and brain of treated animals. It was found that HI-6 does not increase GR or TBARS. On the contrary, TBARS levels in the brain and liver were found to be significantly decreased in HI-6-treated animals. Pertinent antioxidant properties of HI-6 were excluded by the FRAP method. Endogenous antioxidants were unchanged, with the exception of the kidney. Low-molecular-weight antioxidants assayed by the FRAP method were significantly decreased in kidneys of animals treated with HI-6. However, GSH partially recovered the loss of the other low-molecular-weight antioxidants and was significantly increased in the kidney of HI-6-exposed mice. HI-6 potential to produce nephropathy is hypothesized. The achieved conclusions were quite surprising and showed a complex impact of HI-6 on the body. [ABSTRACT FROM AUTHOR]

Abstract: Administration of acetylcholinesterase (AChE) reactivators (oximes) is usually used in order to counteract the poisoning effects of nerve agents. The possibility was suggested that oximes may show some therapeutic and/or adverse effects through their action in central nervous system. There are no sufficient data about interaction of oximes with monoaminergic neurotransmitter''s systems in the brain. Oxime-type AChE reactivators pralidoxime, obidoxime, trimedoxime, methoxime and HI-6 were tested for their potential to affect the activity of monoamine oxidase of type A (MAO-A) and type B (MAO-B) in crude mitochondrial fraction of pig brains. The compounds were found to inhibit fully MAO-A with half maximal inhibitory concentration (IC 50) of 0.375mmol/l (pralidoxime), 1.53mmol/l (HI-6), 2.31mmol/l (methoxime), 2.42mmol/l (obidoxime) and 4.98mmol/l (trimedoxime). Activity of MAO-B was fully inhibited by HI-6 and pralidoxime only with IC 50 4.81mmol/l and 11.01mmol/l, respectively. Methoxime, obidoxime and trimedoxime displayed non-monotonic concentration dependent effect on MAO-B activity. Because oximes concentrations effective for MAO inhibition could not be achieved in vivo at the cerebral level, we suppose that oximes investigated do not interfere with brain MAO at therapeutically relevant concentrations. [Copyright &y& Elsevier]

Current treatment of organophosphate poisoning is insufficient, and survivors may suffer from long-lasting adverse effects, such as cognitive deficits and sleep-wake disturbances. In the present study, we aimed at developing a guinea pig model to investigate the benefits of immediate and delayed stand-alone therapy on the development of clinical signs, EEG, heart rate, respiration and AChE activity in blood and brain after soman poisoning. The model allowed the determination of the therapeutic effects at the short-term of obidoxime, atropine and physostigmine. Obidoxime exerted the highest therapeutic efficacy at administration of the lowest dose (3.1 mg/kg i.m.), whereas two higher doses (9 and 18 mg/kg) were less effective on most parameters. Addition of atropine at 0.03 and 3 mg/kg (i.m.) to the treatment did not improve the therapeutic effects of obidoxime alone. Physostigmine (0.8 mg/kg im) at 1 min after poisoning increased mortality. Two lower doses (0.1 and 0.3 mg/kg i.m.) showed improvements on all parameters but respiration. The middle dose was most effective in preventing seizure development and therefore assessed as the most efficacious dose. Combined treatment of obidoxime and physostigmine shortened the duration of seizures, if present, from up to 80 min to ~10-15 min. In practice, treatment will be employed when toxic signs appear, with the presence of high levels of AChE inhibition in both blood and brain. Administration of physostigmine at that moment showed to be redundant or even harmful. Therefore, treatment of OP poisoning with a carbamate, such as physostigmine, should be carefully re-evaluated. [ABSTRACT FROM AUTHOR]

Abstract: A series of bis-pyridinium oximes connected by xylene linkers were synthesized and their in vitro reactivation potential was evaluated against human acetylcholinesterase (hAChE) inhibited by nerve agent sarin and the data were compared with 2-PAM and obidoxime. Among the synthesized compounds, N,N′-p-xylene-bis-[(2,2′-hydroxyiminomethyl)pyridinium] dibromide (3c) was found to be the most potent reactivator for hAChE inhibited by sarin. The oxime 3c exhibited 45% regeneration of inhibited hAChE, in comparison to 34% and 24% regeneration by 2-PAM and obidoxime, respectively, at a concentration of 10−3 M within 10min. The higher reactivation efficacies of these oximes were attributed to their acid dissociation constants (pKa). The pKa values of all the oximes were determined spectrophotometrically and correlated with their observed reactivation potential. This method involving the in vitro reactivation of inhibited hAChE may be useful for the screening of new oximes as reactivators. [ABSTRACT FROM AUTHOR]

Intoxication with organophosphorous nerve agents such as paraoxon requires immediate administration of antidotes such as oximes. However, the oximes lack sufficient activity in the central nervous system as they are unable to rapidly penetrate the blood-brain barrier (BBB) in therapeutically relevant concentrations. Human serum albumin (HSA) nanoparticles represent a promising drug carrier system for the transport of drugs across the BBB. This study focussed on the development of an obidoxime-loaded nanoparticles prepared by desolvation using an incorporation technique. The nanoparticle preparation parameters, i.e. drug amount, pH value, ethanol volume and crosslinking degree, were optimised. The in vitro release study showed a sustained release profile, indicating the suitability of the developed formulation for the transport of oximes across the BBB. [ABSTRACT FROM AUTHOR]

Abstract: A series of bis-pyridinium oximes connected by methoxy alkane linkers were synthesized and their in vitro reactivation efficacy was evaluated against sarin-inhibited human AChE, and data were compared with 2-PAM and obidoxime. Among the synthesized compounds, 1,2-dimethoxy ethylene bis-[4,4′-(hydroxyiminomethyl) pyridinium] dichloride (4P-2) and 1,2-dimethoxy ethylene bis-[3,3′-(hydroxyiminomethyl) pyridinium] dichloride (3P-2) were found to be the most potent reactivators of human AChE inhibited by nerve agent sarin. The oximes 4P-2 and 3P-2 exhibited 41% and 36% regeneration of sarin-inhibited AChE, respectively, whereas 2-PAM showed 32% regeneration. The higher reactivation efficacy of the oximes was attributed to their acid dissociation constants (pK a). The pK a values of all the oximes were determined by UV–vis spectrophotometric method and correlated with their observed reactivation potential. Overall, the study reveals that the oxime 4P-2 may have therapeutic potential in the reactivation of human AChE inhibited by sarin. [ABSTRACT FROM AUTHOR]

Abstract: 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 10–20μM 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 (250mg i.v. as bolus, followed by 750mg/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±1726mg obidoxime was infused over 65h±55h resulting in a steady state plasma concentration of 14.5±7.3μM. Obidoxime was eliminated with t 1/2(1) 2.2 and t 1/2(2) 14h. 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. [Copyright &y& Elsevier]

The standard treatment of poisoning by organophosphorous compounds such as paraoxon includes the administration of oximes. Due to their inability to rapidly cross the blood–brain barrier (BBB) in therapeutically relevant concentrations, these drugs possess insufficient activity in the central nervous system. Since human serum albumin (HSA) nanoparticles enable the delivery of a variety of drugs across the BBB into the brain, in the present study the antidote obidoxime was bound to these particles by adsorption. The resulting sorption isotherms showed a best fit to Langmuir isotherms indicating that obidoxime adsorbs to HSA nanoparticles forming a monolayer. A maximum drug loading of 93.5 µg obidoxime/mg of nanoparticles at pH 8.3 was calculated. At higher concentrations the particle diameter increased significantly with obidoxime concentration leading to instable particle systems. The in vitro release of obidoxime from HSA nanoparticles showed a rapid release of the drug from the nanoparticles within 3 h. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The potency of newly developed reactivators of nerve agent–inhibited acetylcholinesterase (K347, K628) in reactivating tabun-inhibited acetylcholinesterase and reducing tabun-induced lethal toxic effects was compared with currently available oximes (obidoxime, the oxime HI-6), using in vivo methods. Studies that determined the percentage of reactivation of tabun-inhibited blood and tissue acetycholinesterase in poisoned rats showed that the reactivating efficacy of both newly developed oximes is comparable with the oxime HI-6, but it is significantly lower than the reactivating effects of obidoxime. The monopyridinium oxime, K347, was also found to be able to reduce lethal toxic effects in tabun-poisoned mice, while the therapeutic efficacy of another newly developed bispyridinium oxime, K628, was negligible. The therapeutic efficacy of K347 was higher than the potency of the oxime, HI-6, but it was lower than the therapeutic effects of obidoxime. Thus, the reactivating and therapeutic potency of both newly developed oximes (K347, K628) was not more effective then currently available oximes, and therefore, they are not suitable for the replacement of commonly used oximes (especially obidoxime) for the treatment of acute tabun poisoning. [ABSTRACT FROM AUTHOR]