Effects of subchronic pyridostigmine pretreatment on the toxicity of soman

The effect of subchronic pyridostigmine pretreatment on the toxicity of soman, in the absence of supporting therapy (atropine, oxime, and (or) anticonvulsant), as well as its effect on muscarinic cholinoceptor binding characteristics was assessed in the rat. Pretreatment with pyridostigmine by means of an implanted Alzet osmotic minipump for a 5-day total exposure dose of 12 mg/kg inhibited whole blood acetylcholinesterase activity by 73%. This pyridostigmine pretreatment lowered the soman LD50 from 104 micrograms/kg in control animals to 82 micrograms/kg. In addition, the time to onset of soman-induced convulsions in pyridostigmine pretreated animals was significantly (p less than 0.001) reduced. Pyridostigmine pretreatment produced no significant effect on muscarinic cholinoceptor binding in brain or ileum. Lower doses of pyridostigmine pretreatment inhibited acetylcholinesterase activity (65 and 25%); however, LD50 and time to onset of convulsions following soman (140 micrograms/kg) were not significantly different from controls.     

Antidote effect of sodium fluoride against organophosphate poisoning in mice

Pretreatment of mice with atropine (17.4 mg/kg) + NaF (5 or 15 mg/kg) had a significant antidotal effect over atropine alone against the lethality produced by soman and sarin. Atropine + NaF (15 mg/kg) was effective against tabun, whereas the lower dose of NaF was not. An effect of NaF on organophosphate inhibited acetylcholinesterase could not account for the antidotal action of NaF. NaF had no effect on liver somanase activity but inhibited aliesterase activity. Aliesterase activity in NaF pretreated somanpoisoned mice was significantly (p < 0.05) higher than in those receiving atropine alone. In CBDP-pretreated mice NaF did not significantly attenuate the toxicity of soman. It is hypothesized that the antidotal effect of NaF versus organophosphate poisoning is due to its antidesensitizing action at nicotinic receptors in the neuromuscular junction and/or sympathetic ganglia in addition to the proposed increased hydrolysis of sarin and direct detoxification of tabun.     

Oxime-induced decarbamylation and atropine/oxime therapy of guinea pigs intoxicated with pyridostigmine

The generally accepted explanation for the effects of oximes in countering organophosphorus (OP) anticholinesterase is reactivation of the inhibited acetylcholinesterase (AChE). With soman, the inhibited AChE rapidly becomes resistant to oxime reactivation due to a phenomenon called aging. Thus, pretreatment with pyridostigmine (Py) or physostigmine (Ph) followed by atropine sulfate therapy is required to achieve significant protection against soman; the effectiveness of a pretreatment/therapy (P/T) regimen can be further increased against certain OPs (e.g. sarin and VX) by including an oxime in the therapy regimen. The P/T regimen is clouded by a controversy concerning the use of oximes in the treatment of carbamate intoxication, because 2-PAM has been reported to exacerbate intoxication by some carbamates and to have no effect on decarbamylation rates. To better understand the role of oxime therapy in the theory of pretreatment of OP intoxication we examined the effects of 2-PAM and HI-6 on the rate of decarbamylation of Py-inhibited erythrocyte AChE in vitro and in vivo, and studied the effects of atropine plus 2-PAM or HI-6 on Py toxicity. In decarbamylation experiments, Py-inhibited guinea pig erythrocytes were washed free of excess Py and incubated with vehicle or oxime (2 X 10(-4) M, pH 7.3 and 37 degrees C). Aliquots were assayed for AChE activity at various times during a 60 min incubation period. Rate constants were calculated and compared to determine whether the presence of oxime affected decarbamylation. The data from in vitro and in vivo experiments revealed that oximes accelerated the decarbamylation (p less than 0.05) of inhibited AChE. Lethality data for Py-treated guinea pigs showed that treatment with atropine (23 mumoles/kg, im) plus 2-PAM or HI-6 (145 mumoles/kg, im) at one min after injection of Py increased the protective ratio from 4.2 (atropine only) to 5.1 and 12.2, respectively. It is suggested that the enhanced therapeutic efficacy of atropine by oximes against Py intoxication is related to oxime-induced reactivation.     

Relationship between reversible acetylcholinesterase inhibition and efficacy against soman lethality

Carbamate pretreatment (45% inhibition, reversible), combined with therapy, protected rats from soman-induced lethality [The Pharmacologist 23, 224 (1981)]. The present study was done to see if less than 45% inhibition protects and to see if reversible acetylcholinesterase (AChE) inhibition and efficacy against soman lethality are correlated. At 30 min pre-soman, guinea pigs and rats received (im) either pyridostigmine (Py) or physostigmine (Ph) to inhibit whole blood AChE from 10 to 70%; at 1 min post-soman (sc), they received (im) atropine (16 mg/kg)/2-PAMCl (50 mg/kg) and mecamylamine (0.8 mg/kg)/atropine (16 mg/kg), respectively. Protective ratios (PRs) were computed and they ranged from 3.1 to 7.7 for guinea pigs and from 1.8 to 2.4 for rats. In guinea pigs the PRs for Py + therapy were roughly similar to those of Ph + therapy. In both species at 30 min after im injection of Py and Ph, a linear relationship was found between percentage of whole blood AChE inhibition and ln dosage of carbamate. Positive correlation (p less than 0.05) was found between the degree of reversible AChE inhibition by pretreatment, coupled with therapy, and efficacy against soman lethality. The present data indicate that inhibition levels as low as 10% may provide some protection.     

Tenocyclidine treatment in soman-poisoned rats--intriguing results on genotoxicity versus protection

This study aimed to evaluate the antidotal potency of tenocyclidine (TCP) that probably might protect acetylcholinesterase (AChE) in the case of organophosphate poisoning. TCP was tested alone as a pretreatment or in combination with atropine as a therapy in rats poisoned with (1/4) and (1/2) of LD(50) of soman. Possible genotoxic effects of TCP in white blood cells and brain tissue were also studied. Results were compared with previous findings on the adamantyl tenocyclidine derivative TAMORF. TCP given alone as pretreatment, 5 min before soman, seems to be superior in the protection of cholinesterase (ChE) catalytic activity in the plasma than in brain, especially after administration of the lower dose of soman. Plasma activities of the enzyme after a joint treatment with TCP and soman were significantly increased at 30 min (P<0.001) and 24 h (P=0.0043), as compared to soman alone. TCP and atropine, given as therapy, were more effective than TCP administered alone as a pretreatment. The above therapy significantly increased activities of the enzyme at 30 min (P=0.046) and 24 h (P<0.001), as compared to controls treated with (1/4) LD(50) of soman alone. Using the alkaline comet assay, acceptable genotoxicity of TCP was observed. However, the controversial role of TCP in brain protection of soman-poisoned rats should be studied further.     

Effects of inhibitors of acetylcholine synthesis on brain acetylcholine and survival in soman-intoxicated animals

The effects of hemicholinium-3 (HC-3) or 4-(1-naphthylvinyl)pyridine (4-NVP) alone and together with cholinolytics and/or cholinesterase inhibitors on brain acetylcholine (ACh) levels and survival were studied. Intracerebroventricular (ICVT) injection of 10 μg HC-3 280 min before euthanasia by microwave irradiation reduced rat cerebral ACh levels from 28.4 to 5.4 nmoles ACh/g wet tissue. In rats pretreated with HC-3 alone or with other pretreatment drugs prior to giving up to 2.7 LD50 of soman, iv, cerebral ACh levels increased very little, but in animals not receiving HC-3, brain ACh levels increased to 67.1 nmoles. Treatment of unpoisoned rats with 4-NVP resulted in a significant (26%) reduction in ACh. The inclusion of atropine with 4-NVP resulted in a further reduction in ACh. Pretreatment with 4-NVP caused sign-free doses of physostigmine to produce toxic signs in rabbits and did not enhance the efficacy of carbamate pretreatment against soman. Pretreatment of rabbits with pyridostigmine and atropine methyl nitrate (AMN) failed to provide any protection against soman, but when HC-3, ICVT, was included with those drugs, the protective ratio (PR) against soman was increased from 0.8 to 7.3. These data are consistent with the hypothesis that excess ACh is a primary lesion in organophosphorus anticholinesterase intoxication and that the central nervous system is quite sensitive to excesses of ACh.     

The ganglionic blocking properties of the cholinesterase reactivator, HS-6.

Following intravenous administration of the cholinesterase reactivator HS-6 (30 mg/kg), blood pressure fell (up to 50 mmHg) and maximal blood levels of HS-6 reached 242 microgram/ml. HS-6 attenuated the pressor response resulting from carotid occlusion and the depressor effect of vagal stimulation. Doses of HS-6 below those used to protect against soman in different animal species (10--30 mumol/kg) progressively blocked the ganglion-stimulating effects of nicotine and dimethylphenylpiperazinium but not the pressor effect following adrenaline, a pattern similar to that produced by hexamethonium but only 1/84 as potent. HS-6, like hexamethonium and mecamylamine, progressively blocked the contraction of the nictitating membrane of the cat resulting from preganglionic stimulation. The results indicate that HS-6 possesses ganglion-blocking properties at doses likely to be used in the protection against soman poisoning. The ganglion-blocking properties of the drug may be a factor in the beneficial effects of HS-6.     

Brain neuronal RNA metabolism during acute soman toxication: Effects of antidotal pretreatments

Effects of various antidotal treatments on neuronal RNA contents and on soman induced RNA and acetylcholinesterase (AChE) depletion were monitored using quantitative cytochemical techniques. In rats treated only with antidotes, atropine depressed whereas pralidoxime (2-PAM) elevated RNA contents of both caudate and cerebrocortical (Layer V) neurons. Soman produced a virtually complete inhibition of AChE activity and a moderate decline in neuronal RNA contents. Atropine pretreatment partially restored neuronal RNA levels. Atropine+2-PAM prophylaxis eventuated in a complete restoration of RNA levels but no reactivation of AChE. Addition of physostigmine to the atropine +2-PAM treatment regimen resulted in appreciable AChE reactivation but reduced RNA levels. The overall data indicate that: (1) soman-induced neuronal RNA depletion can be completely reversed by antidotal pretreatment; (2) no precise relationship exists between the extents of antidote-induced restoration of RNA and AChE levels; and (3) 2-PAM exerts marked effects on the brain neuronal network which are unrelated to AChE reactivation. It is postulated that effects of soman and antidotes on neuronal RNA metabolism may signify alterations in acetylcholine (ACh) sensitivity and that pharmacologic manipulation of ACh responsiveness during organophosphate cholinesterase poisoning may be a mechanism for additional therapeutic intervention.     

Time Course,Behavioral Safety,and Protective Efficacy of Centrally Active Reversible Acetylcholinesterase Inhibitors in Cynomolgus Macaques

Galantamine hydrobromide and (?)huperzine A, centrally active reversible acetylcholinesterase inhibitors, are potentially superior to the current standard, pyridostigmine bromide, as a pretreatment for organophosphorus chemical warfare nerve agent intoxication. Galantamine, huperzine, and pyridostigmine were compared for time course of acetylcholinesterase inhibition in 12 cynomolgus macaques. Although both galantamine and huperzine shared a similar time course profile for acetylcholinesterase inhibition, huperzine was 88 times more potent than galantamine. The dose for 50% acetylcholinesterase inhibition (ID₅₀) was 4.1 ug/kg for huperzine, 362 ug/kg for galantamine, and 30.9 ug/kg for pyridostigmine. In a safety assessment, galantamine, huperzine, and pyridostigmine were examined using an operant time-estimation task. Huperzine and pyridostigmine were devoid of behavioral toxicity, whereas galantamine was behaviorally toxic at doses producing peak acetylcholinesterase inhibition of about 50% and higher. Following pretreatment with galantamine, huperzine or pyridostigmine, monkeys were challenged with the median lethal dose of soman at the time of peak acetylcholinesterase inhibition and evaluated for overt signs of soman toxicity (cholinergic crisis, convulsions). Both huperzine and galantamine were equally effective at preventing overt signs of soman toxicity, but neither drug was capable of preventing soman-induced neurobehavioral disruption. In contrast, three of four pyridostigmine-pretreated animals exposed to soman exhibited convulsions and required therapy. Full functional recovery required 3–16 days. The degree of acetylcholinesterase inhibition was lower for pyridostigmine, but rates of recovery of acetylcholinesterase activity following soman challenge were comparable for all drug pretreatments. Huperzine may be the more promising centrally active reversible acetylcholinesterase inhibitor due to its greater potency and superior safety profile.     

Endogenous oxytocin excites phasic contraction of gallbladder in rabbits through oxytocin receptor

These experiments were performed to study the effect of oxytocin (OT) and it's specific receptor on gallbladder motility in rabbits. The fasted New Zealand white rabbits (2.0-2.5 kg) were anaesthetized by urethane (1 g/kg). The gallbladder pressure was recorded continuously to monitor the gallbladder motility. Systemic OT (0.01, 0.02, 0.04 mg/kg, iv) did not affect the gallbladder pressure, but dose-dependently increased the frequency of phasic contraction. Five min after OT administration (0.04 mg/kg, iv), the strength of phasic contraction increased to 0.23 +/- 0.08 mmHg/min (P < 0.01, n = 6). The gallbladder motility returned to normal 15 min later after OT treatment. Intravenous injection of atosiban (0.04 mg/kg, iv), an OT receptor antagonist, decreased the strength of gallbladder phasic contraction but did not affect gallbladder pressure. Pretreatment of atosiban (0.04 mg/kg, iv) completely abolished the systemic OT effect on gallbladder. Vasopressin (VP) (0.1 - 0.5 IU/kg, iv) dose-dependently decrease the gallbladder pressure but did not affect the phasic contraction. MK-329 (0.4 mg/kg, iv), the CCK-A receptor antagonist, L-365, 260 (0.4 mg/kg, iv), the CCK-B receptor antagonist and atropine (0.2 mg/kg, iv), the M receptor antagonist, did not affect the OT effect on gallbladder motility. We suggest that endogenous OT regulates gallbladder phasic contraction through specific OT receptor. This effect is independent of the peripheral CCK and M receptors.     

Chronic vs acute carbamate administration in exercising rats

Physostigmine (PH), alone, and pyridostigmine (PY), in combination with atropine and 2-PAM, have been shown to protect animals against organophosphate poisoning. While acute administration of either of these carbamates increased heating rates and decreased endurance of exercising rats, chronically administered PY did not induce these decrements, and we hypothesized that chronic administration of PH could also result in similar attenuation of these effects. Thus, PH was administered acutely (iv) or chronically (osmotic mini-pump) in the following 4 groups (510-530g, male, N = 10/group): C (control, saline iv), AC-200 (acute, 200 ug/kg, 58% whole blood cholinesterase (ChE) inhibition), CH-7 (chronic, 125 ug/hr, 7 days, 60% inhib.), and CH-14 (chronic, 125 ug/hr, 14 days, 56% inhib.). Rats were run (11 m/min, 26 degrees C) to exhaustion. The run times and heating rates (% of control) were: AC-200 - 47, 213%; CH-7 - 60, 157%; CH-14 - 92, 109%. Additionally, ultrastructural changes noted in diaphragms of acutely treated animals were less evident in chronically treated animals. Thus, the decremental effects of acute PH administration on endurance, thermoregulation, and ultrastructure were attenuated with chronic administration at similar levels of ChE inhibition.     

A conjugate of pyridine-4-aldoxime and atropine as a potential antidote against organophosphorus compounds poisoning

A conjugate of pyridine-4-aldoxime and atropine (ATR-4-OX) was synthesized and its antidotal efficiency was tested in vitro on tabun- or paraoxon-inhibited acetylcholinesterase (AChE) of human erythrocytes as well as in vivo using soman-, tabun- or paraoxon-poisoned mice. Its genotoxic profile was assessed on human lymphocytes in vitro and was found acceptable for further research. ATR-4-OX showed very weak antidotal activity, inadequate for soman or tabun poisoning. Conversely, it was effective against paraoxon poisoning both in vitro and in vivo. All animals treated with 5 % or 25 % LD(50) doses of the new oxime survived after administration of 10.0 or 16.0 LD(50) doses of paraoxon, respectively. Based on the persistence of toxicity symptoms in mice, the atropine moiety had questionable effects in attenuating such symptoms. It appears that ATR-4-OX has a therapeutic effect related to the reactivation of phosphylated AChE, but not to receptor antagonization.     

Effects of soman and its antidotes on tracheal mucociliary transport of ferrets

The purpose of this study was to examine the role of acetylcholinesterase on mucociliary transport by use of a potent anticholinesterase agent, soman, and potential antagonists, atropine (muscarinic antagonist) and pralidoxime (acetylcholinesterase reactivator). Initial measurements of mucociliary transport rate were obtained in anesthetized ferrets at 30-min intervals for 5.5 h. These rates remained constant at a mean of 18.2 +/- 1.0 (SE) mm/min. We studied the effects of intravenously administered soman (1-8 micrograms/kg) and observed a dose-related change in the rate of mucociliary transport [-1.1 +/- 2.7 (SE) mm/min after 1 microgram/kg, 9.8 +/- 2.9 mm/min after 5 micrograms/kg, and 14.4 +/- 4.3 mm/min after 8 micrograms/kg of soman]. Pretreatment with atropine completely prevented the response to soman, whereas pretreatment with pralidoxime did not significantly alter the response. We postulate that soman's effect on mucociliary transport relates directly to its cholinergic activity. Failure of pralidoxime to inhibit the effects of soman may relate to pralidoxime's inability to reactivate acetylcholinesterase successfully.     

Effects of pretreatment with 8018 on the toxicokinetics of soman in rabbits and distribution in mice

The effects of 8018 [3-(2'-phenyl-2'-cyclopentyl-2'-hydroxyl-ethoxy)quinuclidine] on the elimination of soman in rabbits blood and distribution in mice brain and diaphragm were investigated using the chirasil capillary gas chromatographic analysis method. In all experiments, the concentration of P(+)soman was below the detection limit (<0.1 ng x mL(-1)). 8018 (1 mg x kg(-1), im, 10 min pre-treated) could significantly reduce the concentration of P(-)soman in rabbit blood from 53.6 +/- 13.3 to 26.2 +/- 9.70 ng x mL(-1) blood as compared to soman-treated control animal at 15 s following soman injection (43.2 microg x kg(-1), iv). Toxicokinetic parameters showed 8018 could increase clearance (CL((S))) from 20.8 +/- 1.54 to 38.2 +/- 15.3 mLx kg(-1) x s(-1) and reduce AUC of P(-)soman from 2.08 +/- 0.151 to 1.30 +/- 0.564 mg x s x L(-1). 8018 could reduce the concentration P(-)soman in diaphragm from 74.7, 70.5, 88.7 ng x g(-1) to 54.5 45.6, 50.0 ng x g(-1) at the time of 30, 90, 120 s after intoxication of soman subcutaneously vs. soman control respectively, but it had no influence on the concentration of free P(-)soman in brain. Isotope trace experiments showed that it could significantly increase the distribution amount of bound [3H]soman in mice plasma and small intestine during 0-120 min after mice received [3H]soman (0.544 GBq.119 microg x kg(-1), sc) compared to soman control group.     

Effects of diazepam on soman-induced brain neuronal RNA depletion and lethality in rats

Studies were conducted to determine effects of the benzodiazepine anticonvulsant diazepam on soman induced brain neuronal RNA depletion and lethality in rats. Quantitative azure B-RNA cytophotometry was used to monitor RNA responses of cerebrocortical (layer V) and striatal neurons following dosages of 0.5, 0.9 and 1.5 LD50 soman (LD50 = 135 micrograms/kg, sc), whereas mean time of death and 24-h survival following 0.8, 1.2 and 1.5 LD50 were used to assess the antidotal efficacy of diazepam (2.2 mg/kg, im) pretreatment. Soman produced dose-dependent RNA depletion in both brain regions. This RNA impairment was almost completely prevented by diazepam, although neuronal RNA contents were generally slightly lower than corresponding control values. However, diazepam pretreatment was not associated with any change in mean time of death or in 24-h survival. The overall data suggest that excessive neural activity per se may underlie the genesis of soman-induced central metabolic impairments, but also appear to effectively dissociate epileptiform activity from lethal actions of soman.     

New bispyridinium oximes: In vitro and in vivo evaluation of their biological efficiency in soman and tabun poisoning

Improving the efficacy of antidotal treatment of poisonings with nerve agents is still a challenge for the scientific community. This study investigated the interactions of four bispyridinium oximes with human erythrocyte acetylcholinesterase (AChE) and their effects on soman- and tabun-poisoned mice. Oximes HI-6 and TMB-4 were used for comparison. These oximes inhibited AchE with inhibitory potency (IC₅₀) ranging from 0.02 to 1.0 mM. The best reactivating potency (%R) was obtained with K074, when AChE was inhibited by tabun. The protective potency (P₅₀) of all oximes in human erythrocyte AChE inhibited by soman and tabun could not be determined. In tabun-poisoned mice very good antidotal efficacy was obtained with K027, K048, and K074, which makes them interesting for future investigation. The combination of HI-6 and atropine is the therapy of choice for soman poisoning.     

New bispyridinium oximes: in vitro and in vivo evaluation of their biological efficiency in soman and tabun poisoning

Improving the efficacy of antidotal treatment of poisonings with nerve agents is still a challenge for the scientific community. This study investigated the interactions of four bispyridinium oximes with human erythrocyte acetylcholinesterase (AChE) and their effects on soman- and tabun-poisoned mice. Oximes HI-6 and TMB-4 were used for comparison. These oximes inhibited AchE with inhibitory potency (IC(50)) ranging from 0.02 to 1.0 mM. The best reactivating potency (%R) was obtained with K074, when AChE was inhibited by tabun. The protective potency (P(50)) of all oximes in human erythrocyte AChE inhibited by soman and tabun could not be determined. In tabun-poisoned mice very good antidotal efficacy was obtained with K027, K048, and K074, which makes them interesting for future investigation. The combination of HI-6 and atropine is the therapy of choice for soman poisoning.     

Pretreatment with physostigmine, mecamylamine and atropine reduces the impact of soman on the cortical visual evoked potential of the cat

A pretreatment regimen of physostigmine, mecamylamine and atropine was evaluated for its ability to alleviate the impact of soman on visual system function as measured by changes in the cortical visual evoked potential (VEP) of the cat. Data from unprotected animals showed a threshold (30% depression in the VEP) of 6.4 micrograms/kg, while in pretreated animals, the threshold dose was 32.7 micrograms/kg, yielding a protection ratio of 5:1. Extending the time between pretreatment and exposure reduced the degree of protection. Pretreatment also reduced the degree of VEP depression at suprathreshold doses, indicating a therapeutic effect even in cases of severe exposure.     

Carbamate Protection of AChE Against Inhibition by Agricultural Chemicals

The carbamate pyridostigmine bromide has been used as a pretreatment to protect individuals from the nerve agent soman. Previous research showed that pyridostigmine significantly protected human muscle acetylcholinesterase in vitro from soman and bovine red blood cell acetylcholinesterase from some organophosphorous pesticides. Research presented here demonstrates that pretreatment with other carbamates also protects acetylcholinesterase from inhibition by the pesticides chlorpyrifos‐oxon and diazinon‐oxon, but not from malaoxon. © 2012 Wiley Periodicals, Inc. J Biochem Mol Toxicol 26:506‐509, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/jbt.21456     

+]-Huperzine A protects against soman toxicity in guinea pigs

The chemical warfare nerve agent (CWNA) soman irreversibly inhibits acetylcholinesterase (AChE) causing seizure, neuropathology and neurobehavioral deficits. Pyridostigmine bromide (PB), the currently approved pretreatment for soman, is a reversible AChE inhibitor that does not cross the blood–brain barrier (BBB) to protect against central nervous system damage. [−]-Huperzine A, a natural reversible AChE inhibitor, rapidly passes through the BBB and has numerous neuroprotective properties that are beneficial for protection against soman. However, [−]-Huperzine A is toxic at higher doses due to potent AChE inhibition which limits the utilization of its neuroprotective properties. [+]-Huperzine A, a synthetic stereoisomer of [−]-Huperzine A and a weak inhibitor of AChE, is non-toxic. In this study, we evaluated the efficacy of [+]-Huperzine A for protection against soman toxicity in guinea pigs. Pretreatments with [+]-Huperzine A, i.m., significantly increased the survival rate in a dose-dependent manner against 1.2× LD₅₀ soman exposures. Behavioral signs of soman toxicity were significantly reduced in 20 and 40 mg/kg [+]-Huperzine A treated animals at 4 and 24 h compared to vehicle and PB controls. Electroencephalogram (EEG) power spectral analysis showed that [+]-Huperzine A significantly reduces soman-induced seizure compared to PB. [+]-Huperzine A (40 mg/kg) preserved higher blood and brain AChE activity compared to PB in soman exposed animals. These data suggest that [+]-Huperzine A protects against soman toxicity stronger than PB and warrant further development as a potent medical countermeasure against CWNA poisoning.