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An anesthesiological approach to nerve agent victims.

The potential use of weapons of mass destruction has recently become a real threat even in the areas of ongoing armed conflicts. Mass casualty victims can suffer from psychological and physical trauma. The exposure of physically injured patients to a toxic substance, in a scenario of mass injury, has recently gained major attention among planners of future protocols for emergency medical services. Because rapid deterioration and multiorgan involvement are to be expected after physical injuries, proper organization and complex but efficient acute medical care systems must be organized and deployed to ensure a maximal number of saved lives. These victims will inevitably require urgent surgical intervention and prolonged perioperative care. Understanding the interdependence between the toxic and traumatic occurrences and the drugs used to prevent or treat nerve agent intoxication (pyridostigmine bromide, a reversible inhibitor of acetylcholinesterase; atropine, a muscarinic receptor antagonist that is one of the on-site, first aid, pharmacological resuscitation drugs; and oxime-like pralidoxime chloride or obidoxime chloride, acetylcholinesterase reactivators) is vital. In addition, the administration of anesthesia and emergency surgery pose further unpredictable threats to the central nervous system, the cardiovascular system, and respiratory function, all of which may be compromised after chemical intoxication and physical trauma. It is noteworthy that information concerning the effects of nerve agent intoxication among human subjects is derived largely from reports of incidents of intentional terrorist attacks or of accidental exposure to organophosphate pesticides, compounds that are chemically related to nerve agents.

Anesthesia↗

The role of oximes in the management of organophosphorus pesticide poisoning.

The number of intoxications with organophosphorus pesticides (OPs) is estimated at some 3,000,000 per year, and the number of deaths and casualties some 300,000 per year. OPs act primarily by inhibiting acetylcholinesterase (AChE), thereby allowing acetylcholine to accumulate at cholinergic synapses, disturbing transmission at parasympathetic nerve endings, sympathetic ganglia, neuromuscular endplates and certain CNS regions. Atropine is the mainstay of treatment of effects mediated by muscarine sensitive receptors; however, atropine is ineffective at the nicotine sensitive synapses. At both receptor types, reactivation of inhibited AChE may improve the clinical picture. The value of oximes, however, is still a matter of controversy. Enthusiastic reports of outstanding antidotal effectiveness, substantiated by laboratory findings of reactivated AChE and improved neuromuscular transmission, contrast with many reports of disappointing results. In vitro studies with human erythrocyte AChE, which is derived from the same single gene as synaptic AChE, revealed marked differences in the potency and efficacy of pralidoxime, obidoxime, HI 6 and HLö 7, the latter two oximes being considered particularly effective in nerve agent poisoning. Moreover, remarkable species differences in the susceptibility to oximes were revealed, requiring caution when animal data are extrapolated to humans. These studies impressively demonstrated that any generalisation regarding an effective oxime concentration is inappropriate. Hence, the 4 mg/L concept should be dismissed. To antagonise the toxic effects of the most frequently used OPs, pralidoxime plasma concentrations of around 80 mumol/L (13.8 mg/L pralidoxime chloride) should be attained while obidoxime plasma concentrations of 10 mumol/L (3.6 mg/L obidoxime chloride) may be sufficient. These concentrations should be maintained as long as circulating poison is expected to be present, which may require oxime therapy for up to 10 days. Various dosage regimens exist to reach this goal. The most appropriate consists of a bolus short infusion followed by a maintenance dosage. For pralidoxime chloride, a 1 g bolus over 30 minutes followed by an infusion of 0.5 g/h appears appropriate to maintain the target concentrtion of about 13 mg/L (70 kg person). For obidoxime chloride, the appropriate dosage is a 0.25 g bolus followed by an infusion of 0.75 g/24 h. These concentrations are well tolerated and keep a good portion of AChE in the active state, thereby retarding the AChE aging rate. AChE aging is particularly rapid with dimethyl phosphoryl compounds and may thwart the effective reactivation by oximes, particularly in suicidal poisoning with excessive doses. In contrast, patients with diethyl OP poisoning may particularly benefit from oxime therapy, even if no improvement is seen during the first days when the poison load is high. The low propensity to aging with diethyl OP poisoning may allow reactivation after several days, when the poison concentration drops. Rigorous testing of the benefits of oximes is only possible in randomised controlled trials with clear stratification according to the class of pesticides involved, time elapsed between exposure and treatment and severity of cholinergic symptoms on admission.

Animals↗

Inhibition, reactivation and aging kinetics of cyclohexylmethylphosphonofluoridate-inhibited human cholinesterases.

Cyclohexylmethylphosphonofluoridate (cyclosarin) is a highly toxic organophosphate, which was shown to be rather resistant to conventional oxime therapy. To give more insight into the inhibition, reactivation and aging kinetics, human acetyl-(AChE) and butyrylcholinesterase (BChE) were inhibited by cyclosarin (k2 of 7.4 and 3.8 x 10(8) M(-1) min(-1), respectively; pH 7.4, 37 degrees C) and reactivated with obidoxime, pralidoxime and three experimental oximes. The new oxime HLö 7 (1-[[[4-aminocarbonyl)-pyridinio]-methoxy]-methyl]-2,4-bis-[ (hydroxyimino)methyl] pyridinium dimethanesulphonate) was shown to be superior to the other oximes. At oxime concentrations anticipated to be relevant in humans, obidoxime and pralidoxime were extremely weak reactivators of AChE. Aging velocity of BChE was almost fourfold higher compared to AChE (ka of 0.32 h(-1) and 0.08 h(-1), respectively). A substantial spontaneous reactivation was observed with AChE. These results support previous in vivo findings that obidoxime and pralidoxime are insufficient antidotes in cyclosarin poisoning. By contrast, HLö 7 was shown to be an extremely potent reactivator of human AChE and BChE, which supports its position as a broad-spectrum oxime.

Acetylcholinesterase↗

New group of xylene linker-containing acetylcholinesterase reactivators as antidotes against the nerve agent cyclosarin.

Nerve agents such as sarin, cyclosarin and tabun are organophosphorus substances able to inhibit the enzyme acetylcholinesterase (AChE; EC 3.1.1.7). AChE reactivators and anticholinergics are generally used as antidotes in the case of intoxication with these agents. None of the known AChE reactivators is able to reactivate AChE inhibited by all nerve agents used. In this work, reactivation potency of nine newly developed AChE reactivators with an incorporated xylene ring in their structure was measured in vitro. Cyclosarin was chosen as an appropriate member of the nerve agent family. Reactivation potency of the tested AChE reactivators was compared with the gold standard of AChE reactivators--pralidoxime. Two oximes (K107 and K108) surpassed the reactivation potency of pralidoxime. Moreover, from the obtained results it could be deduced that AChE reactivators with a functional oxime group in position-2 are the most potent AChE reactivators in the case of cyclosarin intoxications.

Acetylcholinesterase↗

Comparative evaluation of benzodiazepines for control of soman-induced seizures.

This study evaluated the ability of six benzodiazepines to stop seizures produced by exposure to the nerve agent soman. Guinea pigs, previously prepared with electrodes to record electroencephalographic (EEG) activity, were pretreated with pyridostigmine (0.026 mg/kg, i.m.) 30 min before challenge with soman (56 microg/kg, s.c.) and then treated 1 min after soman exposure with atropine (2.0 mg/kg, i.m.) and pralidoxime chloride (2-PAM Cl; 25 mg/kg, i.m.). All animals developed seizures following this treatment. Benzodiazepines (avizafone, clonazepam, diazepam, loprazolam, lorazepam, and midazolam) were given i.m. 5 or 40 min after seizure onset. All benzodiazepines were effective in stopping soman-induced seizures, but there were marked differences between drugs in the rapidity of seizure control. The 50% effective dose (ED50) values and latencies for anticonvulsant effect for a given benzodiazepine were the same at the two times of treatment delay. Midazolam was the most potent and rapidly acting compound at both treatment times. Since rapid seizure control minimizes the chance of brain damage, use of midazolam as an anticonvulsant may lead to improved clinical outcome in the treatment of nerve agent seizures.

Animals↗

Rectal ulcer with massive haemorrhage due to activated charcoal treatment in oral organophosphate poisoning.

A 42-year-old woman who had ingested a large amount of fenitrothion emulsion was admitted and treated. Treatments consisted of mechanical ventilation, intravenous administration of atropine and pralidoxime and repeated injection of activated charcoal with magnesium sulphate via a nasogastric tube. The patient developed massive rectal bleeding just after she had passed several hard masses of charcoal on the 10th day. Surgical haemostasis of the rectal ulcer was needed to control the haemorrhage.

Adult↗

A comparison of the efficacy of acetylcholinesterase reactivators against cyclohexyl methylphosphonofluoridate (GF agent) by in vitro and in vivo methods.

The purpose of this study was to compare the therapeutic efficacy of a new acetylcholinesterase reactivator, designated BI-6 (1-(2-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium )-2-butene dibromide), with presently used oximes (pralidoxime, obidoxime, methoxime) and H-oximes (HI-6, HLö-7) by in vitro and in vivo methods. In vitro, methoxime seems to be the most efficacious reactivator of GF agent-inhibited acetylcholinesterase because the phosphorylation of acetylcholinesterase by GF agent markedly increases its affinity for the enzyme. The oxime BI-6 is more efficacious than other presently used oximes (pralidoxime, obidoxime) but its reactivating efficacy does not reach the efficacy of H-oximes tested. On the other hand, obidoxime and pralidoxime appear to be very poor reactivators of GF agent-inhibited acetylcholinesterase because the phosphonylation of acetylcholinesterase by GF agent markedly decreases their affinity to the enzyme. In vivo, H oximes (HI-6, HLö-7) are the most efficacious antidotes for the treatment of acute poisoning with GF agent in rats while the presently used oximes such as pralidoxime and obidoxime are practically ineffective. BI-6 and methoxime are more efficacious than pralidoxime and obidoxime, nevertheless their therapeutic efficacy does not reach the efficacy of H oximes. Our results show that the ability of oximes to reactivate GF agent-inhibited acetylcholinesterase in vitro usually corresponds to their therapeutic effects against GF agent in vivo.

Acetylcholinesterase↗

[Comparative study of cases of poisoning by organophosphorous insecticides in various regions of Costa Rica].

336 cases of organophosphorous poisoning from case records of hospitals in Costa Rica between 1972 and 1978 were classified in four categories according to signs and symptoms: 8% latent; 25.9% mild; 43.8% moderate and 22.3% severe. Eighteen of the total patients died during hospitalization. Suicidal ingestion was the principal cause of severe and latent poisoning, especially in urban areas, followed by occupational poisoning in agricultural workers in mild and moderate cases. Occupational poisoning was common in men; in women it was attempted suicide and in children accidental poisoning. Under 40 years of age, the main cause was suicidal ingestion among both men and women, and occupational poisoning after 40 years of age. After discharge from the hospital, 19.6% of the total poisoned patients were referred to psychiatric treatment; 22.7% and 18.2% had had mental and alcoholic problems, respectively, prior to poisoning. Attempted suicide was the principal cause of poisoning in 86.4% of these patients, indicating emotional instability. In this study, the incidence in psychiatric consultation after discharge from the hospital is not indicative of a relationship between mental disorders and acute insecticide poisoning. In 42.6% and in 22% of the deceased patients pralidoxime (PAM) and atropine respectively, were not administered as antidotes in the emergency room. Aminophylline and skeletal muscle relaxants among other contraindicated drugs were administered as part of the treatment in these deceased patients. The consequences of this misguided treatment are questioned.

Adolescent↗

Chemical warfare. Nerve agent poisoning.

The threat of civilian and military casualties from nerve agent exposure has become a greater concern over the past decade. After rapidly assessing that a nerve agent attack has occurred, emphasis must be placed on decontamination and protection of both rescuers and medical personnel from exposure. The medical system can become rapidly overwhelmed and strong emotional reactions can confuse the clinical picture. Initially, care should first be focused on supportive care, with emphasis toward aggressive airway maintenance and decontamination. Atropine should be titrated, with the goal of therapy being drying of secretions and the resolution of bronchoconstriction and bradycardia. Early administration of pralidoxime chloride maximizes antidotal efficacy. Benzodiazepines, in addition to atropine, should be administered if seizures develop. Early, aggressive medical therapy is the key to prevention of the morbidity and mortality associated with nerve agent poisoning.

Animals↗

[The stability of the oxime Hi-6 in eyedrops].

The stability of an efficacious antidote in the treatment of organophosphorous poisoning--HI-6 has been examined in aqueous solutions of eye drops by accelerated stability tests. Disintegration kinetics has been examined at the increased temperatures and pH value of isotonic solution of 25 mg/ml concentration in ampules. First order hydrolysis is larger than in the known oximes: pralidoxime, obidoxime and other due to unfavourable physicochemical properties of HI-6. The period of 44 days which is necessary for reduction of exime concentration in eye drops for 10% at 25 degrees C is not enough for preservation of reliable solution and because of that it should be prepared whenever necessary.

Antidotes↗

Acetylcholinesterase fiber-optic biosensor for detection of anticholinesterases.

An optical sensor for anticholinesterases (AntiChEs) was constructed by immobilizing fluorescein isothiocyanate (FITC)-tagged eel electric organ acetylcholinesterase (AChE) on quartz fibers and monitoring enzyme activity. The pH-dependent fluorescent signal generated by FITC-AChE, present in the evanescent zone on the fiber surface, was quenched by the protons produced during acetylcholine (ACh) hydrolysis. Analysis of the fluorescence response showed Michaelis-Menten kinetics with a Kapp value of 420 microM for ACh hydrolysis. The reversible inhibitor edrophonium (0.1 mM) inhibited AChE and consequently reduced fluorescence quenching. The biosensor response immediately recovered upon its removal. The carbamate neostigmine (0.1 mM) also inhibited the biosensor response but recovery was much slower. In the presence of ACh, the organophosphate (OP) diisopropylfluorophosphate (DFP) at 0.1 mM did not interfere with the ACh-dependent fluorescent signal quenching, but preexposure of the biosensor to DFP in absence of ACh inhibited totally and irreversibly the biosensor response. However, the DFP-treated AChE biosensor recovered fully after a 10-min perfusion with pralidoxime (2-PAM). Echothiophate, a quaternary ammonium OP, inhibited the ACh-induced fluorescence quenching in the presence of ACh and the phosphorylated biosensor was reactivated with 2-PAM. These effects reflected the mechanism of action of the inhibitors with AChE and the inhibition constants obtained were comparable to those from colorimetric methods. The biosensor detected concentrations of the carbamate insecticides bendiocarb and methomyl and the OPs echothiophate and paraoxon in the nanomolar to micromolar range. Malathion, parathion, and dicrotophos were not detected even at millimolar concentrations; however, longer exposure or prior modification of these compounds (i.e., to malaoxon, paraoxon) may increase the biosensor detection limits. This AChE biosensor is fast, sensitive, reusable, and relatively easy to operate. Since the instrument is portable and can be self-contained, it shows potential adaptability to field use.

Acetylcholinesterase↗

Toxicity of organophosphate nerve agents and related phosphonylated oximes compared to their anticholinesterase activity in neuron cultures.

Oximes, such as pralidoxime and toxogonin, are important therapeutic agents for the treatment of organophosphate (OP) nerve agent poisoning. Oximes can react with these nerve agents to give intermediates, phosphonylated oximes, which may be equally toxic to the parent OP. The sc LD50s of a series of phosphonylated 2-butanone and 2,3-butanedione monoximes were compared to the sc LD50s of their parent OPs (tabun, sarin, and VX) in CD-1 mice. In every case the derivatives were significantly less toxic than their parent nerve agents. Times to death, and to signs of poisoning, were inversely proportional to the dose of test compound, and in all mortalities, blood serum acetylcholinesterase (AChE) was severely inhibited. The relative potencies of these compounds, as well as soman, cyclohexyl methylphosphonofluoridate, and diisopropyl fluorophosphate, as inhibitors of AChE in primary cultures of mouse embryo neurons, correlated with their in vivo toxicities. The results indicate that mouse embryo neuron cultures may be a useful model with which to study this class of compounds.

Animals↗

Pharmacokinetic studies of intramuscular midazolam in guinea pigs challenged with soman.

Studies have demonstrated that benzodiazepine compounds are effective at antagonizing seizure activity produced by the organophosphate (OP) cholinesterase inhibitor soman. In this present study we have investigated the pharmacokinetics of midazolam and its associated effects on electroencephalographic (EEG) activity following intramuscular (i.m.) injection to soman-exposed guinea pigs (Crl:(HA)BR). Prior to experiments, the animals were surgically implanted with EEG leads to monitor seizure activity. For the study, animals were administered the following pretreatment/OP/treatment regimen. Pyridostigmine bromide (0.026 mg/kg, i.m.) was given 30 min prior to soman (56 micrograms/kg, 2 x LD50; subcutaneously, s.c.), followed in one minute by atropine sulfate (2 mg/kg, i.m.) and pralidoxime chloride (25 mg/kg, i.m.). All animals receiving this regimen developed seizure activity. Midazolam 0.8 mg/kg, i.m., was administered 5 min after onset of seizure activity. Based on EEG data, animals were categorized as either seizure-terminated or seizure not-terminated at 30 min following anticonvulsant administration. Serial blood samples were collected for the plasma midazolam analysis; the assay was accomplished with a gas chromatograph/mass spectrometer. The mean time to seizure termination was 8.8 +/- 1.6 min. The mean time-plasma concentration data were fit to standard pharmacokinetic models. The following parameter estimates were determined from the model-fit for seizure terminated and not-terminated animals respectively: apparent volumes of distribution (Vd) were 1.4 and 1.7 l/kg; area under the time-concentration curves (AUC), 15,990 and 15,120 ng.min/ml; times to maximal plasma concentration (Tmax), 1.66 and 2.91 min and maximal plasma concentrations (Cmax) 535.1 and 436.6 ng/ml. These data indicate that i.m. injection of midazolam is effective at terminating ongoing soman-induced seizure activity. Additionally, the relatively short Tmax and latency to seizure termination demonstrate the rapidity of drug absorption and action respectively.

Animals↗

A comparison of the efficacy of a new asymmetric bispyridinium oxime BI-6 with currently available oximes and H oximes against soman by in vitro and in vivo methods.

The reactivating and therapeutic efficacy of a new acetylcholinesterase reactivator, designated BI-6(1-/2-hydroxyiminomethylpyridinium/-4-/carbamoylpyridinium+ ++/-2-butene dibromide), against the organophosphate soman was compared with oximes at present used (pralidoxime, obidoxime, methoxime) and H oximes (HI-6, HLö-7) using in vitro and in vivo methods. H oximes HI-6 and HLö-7 seem to be the most efficacious acetylcholinesterase reactivators against soman according to the evaluation of their reactivating and therapeutic efficacy in vitro as well as in vivo. The new oxime BI-6 is not as effective as the H oximes against soman, nevertheless it is significantly more effective against soman than the currently available oximes, pralidoxime, obidoxime and methoxime, which failed to protect rats poisoned with supralethal doses of soman. Our results confirm that the reactivating efficacy of oximes evaluated by the methods in vitro closely correlates not only with the potency of oximes in vivo in reactivating soman-inhibited acetylcholinesterase but also with the ability to protect rats poisoned with supralethal doses of soman.

Animals↗

Prostaglandin antagonism by sodium p-benzyl-4-[1-oxo-2-(4-chlorobenzyl)-3-phenylpropyl]pheenyl phosphonate (N-0164).

1 The ability of sodium p-benzyl-4-[1-oxo-2-(4-chlorobenzyl)-3-phenylpropyl]phenyl phosphonate (N-0164) to antagonize contractions produced by prostaglandins E2 and F2a on isolated preparations of gerbil, rat and guinea-pig gastrointestinal muscle has been studied. 2 N-0164 was found to be a potent, partially selective prostaglandin antagonist in these isolated smooth muscle preparations. The blockade produced by N-0164 in the isolated stomach strip of the rat had some, but not all, the characteristics of a competitive antagonism. 3 N-0164 produced a dose-dependent decrease in tone in the rat stomach strip that was abolished by pretreatment of the preparation with indomethacin. 4 N-0164 prevented diarrhoea induced by prostaglandin E2 in mice when given by intraperitoneal injection but was less effective when given orally. 5 N-0164 inhibited oedema induced with croton-oil and pyridine-ether in the mouse ear. 6 N-0164 delayed the onset of erythema following ultraviolet irradiation of guinea-pig skin only when an equimolar amount of pralidoxime chloride was added to the vehicle. 7 It is concluded that N-0164 is a potent, partially selective prostaglandin antagonist on several isolated smooth msucle preparations. N-0164 exhibits activity in vivo particularly following local application when problems associated with penetration and distribution are minimized.

Animals↗

Organophosphate and carbamate poisoning in infants and children.

The clinical and laboratory features of moderate to severe organophosphate and carbamate toxicity in 37 infants and children are presented. Ingestion of an improperly stored liquid pesticide was the most common route of intoxication (76% of patients); five (14%) children became intoxicated after playing on carpets and floors of homes that had been sprayed or fogged by unlicensed exterminators. The transfer diagnoses were incorrect for 16 or 20 patients who were transferred to our center from another institution. Miosis (73%), excessive salivation (70%), muscle weakness (68%), and lethargy (54%) were the most common abnormal signs; 49% and 22% of patients had tachycardia and seizures, respectively, and 38% of children had respiratory insufficiency that required endotracheal intubation and mechanical ventilation. The results of erythrocyte and serum cholinesterase activity assays were concordant in 83% of patients. Thirty-four (92%) patients were treated with atropine and/or pralidoxime; three patients required only supportive care. Most patients had a prompt response to therapy; however, two patients with organophosphate toxicity required multiple doses of atropine during a 24-hour period; in both instances, the doses of atropine were subtherapeutic. There were no deaths. Pneumonitis and/or atelectasis developed in ten patients, including six who had ingested a petroleum distillate-containing insecticide.

Carbamates↗

Anticonvulsant treatment of nerve agent seizures: anticholinergics versus diazepam in soman-intoxicated guinea pigs.

A total of eight anticholinergic drugs (aprophen, atropine, azaprophen, benactyzine, biperiden, procyclidine, scopolamine, trihexyphenidyl) were tested in parallel with diazepam for the ability to terminate seizure activity induced by the nerve agent soman. Guinea pigs, implanted with electrodes to record cortical electroencephalographic (EEG) activity, were pretreated with pyridostigmine Br (0.026 mg/kg, i.m.) and 30 min later challenged with 2 x LD50 soman (56 microg/kg, s.c.) followed 1 min later by treatment with atropine SO4 (2 mg/kg, i.m.) and pralidoxime chloride (2-PAM Cl; 25 mg/kg, i.m.). All guinea pigs developed sustained seizure activity following this treatment. Dose-effect curves were determined for the ability of each drug to terminate seizure activity when anticonvulsant treatment was given either 5 or 40 min after seizure onset. Body weight gain and recovery of behavioral performance of a previously trained one-way avoidance task were measured after exposure. With the exception of atropine, all anticholinergic drugs were effective at lower doses than diazepam in terminating seizures when given 5 min after seizure onset; benactyzine, procyclidine and aprophen terminated seizures most rapidly while scopolamine, trihexyphenidyl, biperiden, and diazepam were significantly slower. When given 40 min after seizure onset, diazepam was the most potent compound tested, followed by scopolamine, benactyzine and biperiden; atropine was not effective when tested 40 min after seizure onset. For diazepam, the time to terminate the seizure was the same whether it was given at the 5- or 40-min delay. In contrast, most anticholinergics were significantly slower in terminating seizure activity when

Animals↗

In vitro reactivation potency of some acetylcholinesterase reactivators against sarin- and cyclosarin-induced inhibitions.

In our study, we have tested six acetylcholinesterase (AChE) reactivators (pralidoxime, obidoxime, HI-6, trimedoxime, BI-6 and Hlö-7) for reactivation of sarin- and cyclosarin-inhibited AChE using an in vitro reactivation test. We have used rat brain homogenate as the suitable source of enzyme. All oximes are able to reactivate sarin-inhibited AChE. On the other hand, only HI-6 is able to reactivate satisfactorily cyclosarin-inhibited AChE.

Animals↗