Pharmacokinetics following a loading plus a continuous infusion of pralidoxime compared with the traditional short infusion regimen in human volunteers

An unusual double radical homolysis mechanism for the unexpected activation of the aldoxime nerve-agent antidotes by polyhalogenated quinoid carcinogens under normal physiological conditions

We have recently shown that the pyridinium aldoximes, best-known as therapeutic antidotes for chemical warfare nerve-agents, could markedly detoxify the carcinogenic tetrachloro-1,4-benzoquinone (TCBQ) via an unusual double Beckmann fragmentation mechanism. However, it is still not clear why pralidoxime (2-PAM) cannot provide full protection against TCBQ-induced biological damages even when 2-PAM was in excess. Here we show, unexpectedly, that TCBQ can also activate pralidoxime to generate a reactive iminyl radical intermediate in two-consecutive steps, which was detected and unequivocally characterized by the complementary application of ESR spin-trapping, HPLC/MS and nitrogen-15 isotope-labeling studies. The same iminyl radical was observed when TCBQ was substituted by other halogenated quinones. The end product of iminyl radical was isolated and identified as its corresponding reactive and toxic aldehyde. Based on these data, we proposed that the reaction of 2-PAM and TCBQ might be through the following two competing pathways: a nucleophilic attack of 2-PAM on TCBQ forms an unstable transient intermediate, which can decompose not only heterolytically to form 2-CMP via double Beckmann fragmentation, but also homolytically leading to the formation of a reactive iminyl radical in double-steps, which then via H abstraction and further hydrolyzation to form its corresponding more toxic aldehyde. Analogous radical homolysis mechanism was observed with other halogenated quinones and pyridinium aldoximes. This study represents the first detection and identification of reactive iminyl radical intermediates produced under normal physiological conditions, which provides direct experimental evidence to explain only the partial protection by 2-PAM against TCBQ-induced biological damages, and also the potential side-toxic effects induced by 2-PAM and other pyridinium aldoxime nerve-agent antidotes.

In vitro characterization of pralidoxime transport and acetylcholinesterase reactivation across MDCK cells and stem cell-derived human brain microvascular endothelial cells (BC1-hBMECs)

Background

Current therapies for organophosphate poisoning involve administration of oximes, such as pralidoxime (2-PAM), that reactivate the enzyme acetylcholinesterase. Studies in animal models have shown a low concentration in the brain following systemic injection.

Methods

To assess 2-PAM transport, we studied transwell permeability in three Madin-Darby canine kidney (MDCKII) cell lines and stem cell-derived human brain microvascular endothelial cells (BC1-hBMECs). To determine whether 2-PAM is a substrate for common brain efflux pumps, experiments were performed in the MDCKII-MDR1 cell line, transfected to overexpress the P-gp efflux pump, and the MDCKII-FLuc-ABCG2 cell line, transfected to overexpress the BCRP efflux pump. To determine how transcellular transport influences enzyme reactivation, we developed a modified transwell assay where the inhibited acetylcholinesterase enzyme, substrate, and reporter are introduced into the basolateral chamber. Enzymatic activity was inhibited using paraoxon and parathion.

Results

The permeability of 2-PAM is about 2 × 10⁻⁶ cm s⁻¹ in MDCK cells and about 1 × 10⁻⁶ cm s⁻¹ in BC1-hBMECs. Permeability is not influenced by pre-treatment with atropine. In addition, 2-PAM is not a substrate for the P-gp or BCRP efflux pumps.

Conclusions

The low permeability explains poor brain penetration of 2-PAM and therefore the slow enzyme reactivation. This elucidates one of the reasons for the necessity of sustained intravascular (IV) infusion in response to organophosphate poisoning.

Electronic supplementary material

The online version of this article (doi:10.1186/s12987-016-0035-0) contains supplementary material, which is available to authorized users.

Being prepared: emergency treatment following a nerve agent release

Nerve agents are extremely toxic and are some of the most lethal substances on earth. This group of chemicals consists of sarin, cyclosarin, soman, tabun, VX, and VR. It is currently unknown how many countries possess these chemicals and in what quantities. These agents work through altering the transmission and breakdown of acetylcholine by binding to, and inactivating, acetylcholinesterase. This results in an uncontrolled and overwhelming stimulation of both muscarinic and nicotinic receptors. Receptor activation at these sites can lead to a wide variety of clinical symptoms, with death frequently resulting from pulmonary edema. Antidotal therapy in this setting largely consists of atropine, pralidoxime, and benzodiazepines, all of which must be administered emergently to limit the progression of symptoms and prevent the enzyme inactivation from becoming permanent. This article reviews the mechanism of action of the nerve agents and their effects on the human body, the currently available therapies to mitigate their impact, and important therapeutic considerations for health care practitioners in the emergency department.

Toxidromes

The critical care physician is often called to care for poisoned patients. This article reviews the general approach to the poisoned patient, specifically focusing on the utility of the toxidrome. A toxidrome is a constellation of findings, either from the physical examination or from ancillary testing, which may result from any poison. There are numerous toxidromes defined in the medical literature. This article focuses on the more common toxidromes described in clinical toxicology. Although these toxidromes can aid the clinician in narrowing the differential diagnosis, care must be exercised to realize the exceptions and limitations associated with each.

Preparing for chemical terrorism: a study of the stability of expired pralidoxime (2-PAM)

OBJECTIVES

Oximes such as pralidoxime (2-PAM) are essential antidotes for life-threatening organophosphate poisoning. Unfortunately, oximes are expensive, have limited use, and have short shelf lives. As such, maintaining large stockpiles in preparation for terrorist activity is not always possible. We have demonstrated that atropine is stable well beyond its labeled shelf life and that recently expired 2-PAM was clinically efficacious in a series of poisoned patients. Because 2-PAM is often dosed empirically, clinical improvement does not guarantee pharmacological stability. We therefore chose to analyze the chemical stability of expired 2-PAM.

METHODS

Samples of lyophylized 2-PAM were maintained according to the manufacturer's recommendations for 20 years beyond the published shelf life. We studied 2-PAM contained in a MARK I autoinjector that was stored properly for 3 years beyond its expiration date. An Agilent LC/MSD 1100 with diode-array detector and an Agilent Sorbax SB-C-18, 4.6 × 150-mm, 5-μm column were used with the following solvent systems: water with 0.01% trifluoroacetic acid and methanol with 0.01% trifluoroacetic acid. Fresh reagent grade 2-PAM was used as a standard. Results were repeated for consistency.

RESULTS

Lyophylized 2-PAM was a white powder that was clear and colorless in solution. Liquid chromatography was identical to the standard and resulted in 2 isolated peaks with identical mass spectra, suggesting that they are stereoisomers. The autoinjector discharged a clear, yellowish solution. In addition to the 2 peaks identified for lyophylized 2-PAM, a small third peak was identified with a mass spectra corresponding to the reported N -methyl pyridinium carboxaldehyde degradation product.

CONCLUSIONS

When properly stored, lyophylized 2-PAM appears to be chemically stable well beyond its expiration date. Although the relative amount of degradation product found in solubilized (autoinjector) 2-PAM was small, it is unclear whether this may be toxic and therefore is of concern. Further studies performed with lots of drug stored under varied conditions would be required to fully determine the stability of expired 2-PAM.

Oximes for acute organophosphate pesticide poisoning

BACKGROUND

Acute organophosphorus pesticide poisoning causes tens of thousands of deaths each year across the developing world. Standard treatment involves administration of intravenous atropine and oxime to reactivate inhibited acetylcholinesterase. The clinical usefulness of oximes, such as pralidoxime and obidoxime, has been challenged over the past 20 years by physicians in many parts of the world.

OBJECTIVES

To quantify the effectiveness and safety of the administration of oximes in acute organophosphorus pesticide-poisoned patients.

SEARCH STRATEGY

We searched both English and Chinese databases: Cochrane Injuries Group Specialised Register, Cochrane Central Register of Controlled Trials (The Cochrane Library), MEDLINE (Ovid SP), EMBASE (Ovid SP), ISI Web of Science: Science Citation Index Expanded (SCI-EXPANDED), ISI Web of Science: Conference Proceedings Citation Index-Science (CPCI-S) and the Chinese language databases CNKI and WANGFANG. All searches were run in September 2009.

SELECTION CRITERIA

Articles that could possibly be RCTs were retrieved to determine if they were randomised.

DATA COLLECTION AND ANALYSIS

The published methodology of three RCTs was not clear. We contacted the principal authors of these, but did not obtain further information.

MAIN RESULTS

Seven pralidoxime RCTs were found. Three RCTs including 366 patients studied pralidoxime vs placebo and four RCTs including 479 patients compared two or more different doses. These trials found quite disparate results with treatment effects ranging from benefit to harm. However, many studies did not take into account several issues important for outcomes. In particular, baseline characteristics were not balanced, oxime doses varied widely, there were substantial delays to treatment, and the type of organophosphate was not taken into account. Only one RCT compared the World Health Organization (WHO) recommended doses with placebo. This trial showed no clinical benefits and a trend towards harm in all sub-groups, despite clear evidence that these doses reactivated acetylcholinesterase in the blood.

AUTHORS' CONCLUSIONS

Current evidence is insufficient to indicate whether oximes are harmful or beneficial. The WHO recommended regimen (30 mg/kg pralidoxime chloride bolus followed by 8 mg/kg/hr infusion) is not supported. Further RCTs are required to examine other strategies and regimens. There are many theoretical and practical reasons why oximes may not be useful, particularly for late presentations of dimethyl OP and those with a large excess of OP that simply re-inhibits reactivated enzymes. Future studies should screen for patient sub-groups that may benefit and may need flexible dosing strategies as clinical effectiveness and doses may depend on the type of OP.

Pralidoxime in acute organophosphorus insecticide poisoning--a randomised controlled trial

BACKGROUND

Poisoning with organophosphorus (OP) insecticides is a major global public health problem, causing an estimated 200,000 deaths each year. Although the World Health Organization recommends use of pralidoxime, this antidote's effectiveness remains unclear. We aimed to determine whether the addition of pralidoxime chloride to atropine and supportive care offers benefit.

METHODS AND FINDINGS

We performed a double-blind randomised placebo-controlled trial of pralidoxime chloride (2 g loading dose over 20 min, followed by a constant infusion of 0.5 g/h for up to 7 d) versus saline in patients with organophosphorus insecticide self-poisoning. Mortality was the primary outcome; secondary outcomes included intubation, duration of intubation, and time to death. We measured baseline markers of exposure and pharmacodynamic markers of response to aid interpretation of clinical outcomes. Two hundred thirty-five patients were randomised to receive pralidoxime (121) or saline placebo (114). Pralidoxime produced substantial and moderate red cell acetylcholinesterase reactivation in patients poisoned by diethyl and dimethyl compounds, respectively. Mortality was nonsignificantly higher in patients receiving pralidoxime: 30/121 (24.8%) receiving pralidoxime died, compared with 18/114 (15.8%) receiving placebo (adjusted hazard ratio [HR] 1.69, 95% confidence interval [CI] 0.88-3.26, p = 0.12). Incorporating the baseline amount of acetylcholinesterase already aged and plasma OP concentration into the analysis increased the HR for patients receiving pralidoxime compared to placebo, further decreasing the likelihood that pralidoxime is beneficial. The need for intubation was similar in both groups (pralidoxime 26/121 [21.5%], placebo 24/114 [21.1%], adjusted HR 1.27 [95% CI 0.71-2.29]). To reduce confounding due to ingestion of different insecticides, we further analysed patients with confirmed chlorpyrifos or dimethoate poisoning alone, finding no evidence of benefit.

CONCLUSIONS

Despite clear reactivation of red cell acetylcholinesterase in diethyl organophosphorus pesticide poisoned patients, we found no evidence that this regimen improves survival or reduces need for intubation in patients with organophosphorus insecticide poisoning. The reason for this failure to benefit patients was not apparent. Further studies of different dose regimens or different oximes are required.

Chemical Terrorism Attacks: Update on Antidotes

There is well-founded concern that a chemical or radioactive agent will at some point be used as a weapon of terror. There are several antidotes that, if used correctly in a timely fashion, can help lessen the harm caused by these agents. This article is meant to introduce the clinician to several such agents, along with the antidotes useful in the management of exposure to these. It covers the indications, administration, and precautions for using these antidotes.

Continuous pralidoxime infusion versus repeated bolus injection to treat organophosphorus pesticide poisoning: a randomised controlled trial

BACKGROUND

The role of oximes for the treatment of organophosphorus pesticide poisoning has not been conclusively established. We aimed to assess the effectiveness of a constant pralidoxime infusion compared with repeated bolus doses to treat patients with moderately severe poisoning from organophosphorus pesticides.

METHODS

200 patients were recruited to our single-centre, open randomised controlled trial after moderately severe poisoning by anticholinesterase pesticide. All were given a 2 g loading dose of pralidoxime over 30 min. Patients were then randomly assigned to control and study groups. Controls were given a bolus dose of 1 g pralidoxime over 1 h every 4 h for 48 h. The study group had a constant infusion of 1 g over an hour every hour for 48 h. Thereafter, all patients were given 1 g every 4 h until they could be weaned from ventilators. Analysis was by intention to treat. Primary outcome measures were median atropine dose needed within 24 h, proportion of patients who needed intubation, and number of days on ventilation. The study is registered at http://www.clinicaltrials.gov with the identifier NCT00333944.

FINDINGS

100 patients were assigned the high-dose regimen, and 100 the control regimen. There were no drop-outs. Patients receiving the high-dose pralidoxime regimen required less atropine during the first 24 h than controls (median 6 mg vs 30 mg; difference 24 mg [95% CI 24-26, p<0.0001]). 88 (88%) and 64 (64%) of controls and high-dose patients, respectively, needed intubation during admission to hospital (relative risk=0.72, 0.62-0.86, p=0.0001). Control patients required ventilatory support for longer (median 10 days vs 5 days; difference 5 days [5-6, p<0.0001]).

INTERPRETATION

A high-dose regimen of pralidoxime, consisting of a constant infusion of 1 g/h for 48 h after a 2 g loading dose, reduces morbidity and mortality in moderately severe cases of acute organophosphorus-pesticide poisoning.

Oxime therapy and outcomes in human organophosphate poisoning: an evaluation using meta-analytic techniques

OBJECTIVE

The status of oximes in human organophosphate poisoning is controversial. This analysis compares the outcomes of therapy with or without oximes.

DESIGN

Quantitative analysis using meta-analytic techniques.

METHODS

Controlled trials of oximes in human organophosphate poisoning were identified by search of MEDLINE and TOXLINE (1966 to May 2005) and review of published articles.

MEASUREMENTS AND MAIN RESULTS

Of the 3,122 articles on organophosphate poisoning identified by electronic search, 116 related to oxime use in human organophosphate poisoning. Seven trials, including two randomized controlled trials, compared oximes with standard medical care. Varying dosage schedules of pralidoxime or obidoxime were used. The effects of oxime therapy on mortality rate, mechanical ventilation, incidence of intermediate syndrome, and need for intensive care therapy were analyzed and expressed as risk difference (positive values indicating oxime harm). The random effects estimator was reported because of underlying heterogeneity of treatment effects between study types. No statistically significant association of oxime therapy was demonstrated for either mortality (risk difference 0.09, 95% confidence interval -0.08 to 0.27), ventilatory requirements (risk difference 0.16, 95% confidence interval -0.07 to 0.38), or the incidence of intermediate syndrome (risk difference 0.16, 95% confidence interval -0.12 to 0.45), although point estimates of effect suggested harm. An increased need for intensive care therapy (risk difference 0.19, 95% confidence interval 0.01 to 0.36) was apparent with oxime therapy.

CONCLUSIONS

Based on the current available data on human organophosphate poisoning, oxime was associated with either a null effect or possible harm. The lack of current prospective randomized controlled trials, with appropriate patient stratification, mandates ongoing assessment of the role of oximes in organophosphate poisoning.

Organic Phosphorus Compounds—Nerve Agents

The organic phosphorous compounds (OPC) include both the military grade nerve agents and the organic phosphorous pesticides. The major mechanism of OPC toxicity is through inhibition of acetylcholinesterase in neuronal synapses leading to excess acetylcholine and overstimulation of target organs. Signs and symptoms depend on the affinity of the OPC for muscarinic versus nicotinic receptors, and are likely to include both. Muscarinic symptoms may include diarrhea, urination, bronchospasm, bronchorrhea, emesis, and salivation. Nicotinic symptoms such as paralysis and fasciculations may also occur. Central nervous system toxicity may include seizures, altered mental status, and apnea, and require prompt intervention. Treatment includes early airway and ventilatory support as well as antidotal therapy with atropine, pralidoxime, and diazepam. Goals of therapy include prevention and rapid treatment of hypoxia and seizures, as these are linked to patient outcome.

High concentrations of pralidoxime are needed for the adequate reactivation of human erythrocyte acetylcholinesterase inhibited by dimethoate in vitro

Due to the current controversy about the real effectiveness of the oximes in the treatment of organophosphate poisoning, the reactivation capacity of pralidoxime has been evaluated in vitro on human erythrocyte acetylcholinesterase inhibited by dimethoate. In the in vitro model, a partial recovery of acetylcholinesterase activity was observed with concentrations from 0.066 mM pralidoxime, probably useful enough to prevent death in most cases in vivo. However, much more effectiveness was observed with concentrations up to 0.70 mM pralidoxime. Although pralidoxime should be applied as soon as possible after organophosphate exposure, the application of the antagonist can be useful even 24h after, particularly for organophosphates with biological half-life longer than one day. The protective capacity of pralidoxime after the application was reduced up to 50% in 6h and disappeared almost completely in 24h. Furthermore, the pesticide and its metabolites remained active and were able to inhibit the enzyme as soon as pralidoxime reduced its antagonist capacity. Our results in conjunction with the short half-life of pralidoxime suggest that the maintenance of higher plasmatic concentrations than the currently used should be considered in the management of severe poisoned patients, although adverse effects could be expected.

Benefits of magnesium sulfate in the management of acute human poisoning by organophosphorus insecticides

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

Nerve agent toxicity and treatment

The clinical syndrome of nerve agent toxicity varies widely, ranging from the classic cholinergic syndrome to flaccid paralysis and status epilepticus. All nerve agents are capable of producing marked neuropathology. Seizure control is strongly associated with protection against acute lethality and brain pathology. The mainstays of therapy of nerve agent poisoned patients are atropine, pralidoxime, and benzodiazepines. Fosphenytoin provides little therapeutic anticonvulsant effectiveness for nerve agent-induced status epilepticus. Tachycardia is not a contraindication to treatment with atropine in nerve agent toxicity. Atropine should be administered to alleviate respiratory distress, symptomatic bradycardia, and as an adjunct to benzodiazepines and pralidoxime to alleviate seizure activity. In significant nerve agent toxicity, a continuous pralidoxime infusion may be considered.

Oximes for acute organophosphate pesticide poisoning

BACKGROUND

Acute organophosphorus pesticide poisoning causes tens of thousands of deaths each year across the developing world. Standard treatment involves administration of intravenous atropine and oxime to counter acetylcholinesterase inhibition at the synapse. The usefulness of oximes, such as pralidoxime and obidoxime, has been challenged over the past 20 years by physicians in many parts of the world, who have failed to see benefit in their clinical practice.

OBJECTIVES

To find the clinical trial evidence for oximes producing clinical benefit in acute organophosphorus pesticide-poisoned patients.

SEARCH STRATEGY

We carried out a systematic search to find randomised clinical trials (RCTs) of oximes in acute organophosphorus pesticide poisoning, using MEDLINE, EMBASE and Cochrane databases. All articles with the text words 'organophosphate' or 'oxime' together with 'poisoning' or 'overdose' were examined. (Search last updated November 2003.)

SELECTION CRITERIA

Articles that could possibly be randomised clinical trials were retrieved to determine if this was the case.

DATA COLLECTION AND ANALYSIS

The published methodology of the possible RCTs located is not clear. One was found in abstract form only and two other published trials also had many gaps in the published methodology. We have attempted to contact the principal authors of all three trials but have been unable to obtain further information.

MAIN RESULTS

Two RCTs have been published, involving 182 patients treated with pralidoxime. These trials did not find benefit. However, the studies did not take into account a number of issues important for outcome and the methodology is unclear. Therefore, a generalised statement on effectiveness cannot be supported by the published results. In particular, characteristics at baseline were not evenly balanced, the dose of oxime was much lower than recommended in guidelines, there were substantial delays to treatment, and the type of organophosphate was not taken into account. The abstract of the third trial, a small possible RCT, is uninterpretable without further data.

AUTHORS' CONCLUSIONS

Current evidence is insufficient to indicate whether oximes are harmful or beneficial in the management of acute organophosphorus pesticide poisoning. A much larger RCT is required to compare the World Health Organization recommended pralidoxime regimen (>30 mg/kg bolus followed by >8 mg/kg/hr infusion) with placebo. There are many theoretical and practical reasons why oximes may not be useful to patients with overwhelming self-poisoning. Such a study will need to be designed with pre-defined sub-group analysis to allow identification of patient sub-groups that may benefit from oximes.

Measurement of serum pralidoxime methylsulfate (Contrathion®) by high-performance liquid chromatography with electrochemical detection

Pralidoxime methylsulfate (Contrathion) is widely used to treat organophosphate poisoning. Despite animal and human studies, the usefulness of Contrathion therapy remains a matter of debate. Therapeutic dosage regimens need to be clarified and availability of a reliable method for plasma pralidoxime quantification would be helpful in this process. We here describe a high-performance liquid chromatography technique with electrochemical detection to measure pralidoxime concentrations in human serum using guanosine as an internal standard. The assay was linear between 0.25 and 50 microg mL(-1) with a quantification limit of 0.2 microg mL(-1). The analytical precision was satisfactory, with variation coefficients lower 10%. This assay was applied to the analysis of a serum from an organophosphorate poisoned patient and treated by Contrathion infusions (100 and 200 mg h(-1)) after a loading dose (400 mg).

Pediatric poisoning from trimedoxime (TMB4) and atropine automatic injectors

OBJECTIVE

To describe the effects of combined trimedoxime (TMB4) and atropine poisoning from automatic injectors (AI) in children.

STUDY DESIGN

Data was collected from two sources: calls to the Israel Poison Information Center (IPIC) during a 1-year period and a cohort of children who presented to pediatric emergency departments (EDs) after unintentional injection of an AI. Demographic data and data regarding the type of AI, site and time of injection, and the clinical manifestations were abstracted.

RESULTS

Data were available for 142 patients. The median age was 8.5 years (range 1.25-18 years). The dose of atropine and TMB4 was higher than the recommended dose for age in 22 (15.5%) cases. There were few side effects attributable to atropine: dilated pupils (26.7%), dryness of mucous membranes (24.6%), and tachycardia (22.5%). Compared with children injected with an age-appropriate dose, children injected with an AI that contained a dose that exceeds the recommended one were more likely to be symptomatic ( P = .029). There were no side effects characteristic to oximes, and no specific medical intervention was required.

CONCLUSIONS

Unintentional pediatric atropine and TMB4 injection, even an adult dose in a small child, does not cause significant side effects.

Nerve agents: a comprehensive review

Nerve agents are perhaps the most feared of potential agents of chemical attack. The authors review the history, physical characteristics, pharmacology, clinical effects, and treatment of these agents.

Insecticides

Organophosphate (OP) insecticide toxicity is the leading cause of major morbidity and death in the insecticides class. The clinical syndrome of OP toxicity varies widely, ranging from the classic cholinergic syndrome to flaccid paralysis and intractable seizures. The mainstays of therapy for OP-poisoned patients are atropine, pralidoxime, and benzodiazepines. Tachycardia is not a contraindication to treatment with atropine in OP toxicity. Atropine should be administered to alleviate respiratory distress, symptomatic bradycardia, and as an adjunct to benzodiazepines to alleviate seizure activity. Atropine should not be administered systemically to alleviate miosis. In acute OP toxicity, a continuous pralidoxime infusion should be considered. Intermediate syndrome and OP-induced delayed neuropathy may occur in select patients with OP poisoning.

Oximes in acute organophosphorus pesticide poisoning: a systematic review of clinical trials

BACKGROUND

Acute organophosphorus (OP) pesticide poisoning is widespread in the developing world. Standard treatment involves the administration of intravenous atropine and an oxime to counter acetylcholinesterase inhibition at the synapse, but the usefulness of oximes is uncertain.

AIM

To assess the evidence on the use of oximes in OP poisoning.

DESIGN

Systematic review.

METHODS

We searched Medline, Embase, and Cochrane databases (last check 01/02/02) for 'organophosphate' or 'oxime' together with 'poisoning' or 'overdose'. We cross-referenced from other articles, and contacted experts to identify unpublished studies. A Web search engine [www.google.com] was also used, with the keywords 'organophosphate', 'oxime', and 'trial' (last check 01/02/02).

RESULTS

We found two randomized controlled trials (RCTs) involving 182 patients treated with pralidoxime. The RCTs found no benefit with pralidoxime, and have been used to argue that pralidoxime should not be used in OP poisoning.

DISCUSSION

The RCT authors must be congratulated for attempting important studies in a difficult environment. However, their studies did not take into account recently clarified issues regarding outcome, and their methodology is unclear. A generalized statement that pralidoxime should not be used in OP poisoning is not supported by the published results. Oximes may well be irrelevant in the overwhelming self-poisoning typical of the tropics, but a large RCT comparing the current WHO-recommended pralidoxime regimen (>30 mg/kg bolus followed by >8 mg/kg/h infusion) with placebo is needed for a definitive answer. Such a study should be designed to identify any patient subgroups that might benefit from oximes.

Organophosphate pesticides: biochemistry and clinical toxicology

Organophosphate pesticides are used extensively worldwide, and poisoning by these agents, particularly in developing nations, is a serious public health problem. The toxicokinetics and toxicodynamics of organophosphate poisoning vary not only with the route and extent of exposure, but also the chemical structure of the agent. The mechanism of toxicity is the inhibition of acetylcholinesterase, resulting in an accumulation of the neurotransmitter acetylcholine and the continued stimulation of acetylcholine receptors. The standard treatment consists of reactivation of the inhibited acetylcholinesterase with an oxime antidote and reversal of the biochemical effects of acetylcholine with atropine. Patients who receive treatment promptly usually recover from acute toxicity but may suffer from neurologic sequelae.

Severe fenthion intoxications due to ingestion and inhalation with survival outcome

Two cases of severe fenthion intoxication are presented. The first is a case of a psychiatric patient who attempted suicide with ingestion of the compound, and the second case was of a child exposed to the chemical agent by air spraying. Both patients were treated in the intensive care unit with atropine and pralidoxime and finally survived. Fenthion blood levels on admission were 2.7 and 0.95 microg/mL, respectively. Different concentrations of pralidoxime were added to the first patient's poisoned serum in order to assess in vitro the effect of pralidoxime on cholinesterase reactivation. The clinical and toxicological data of the poisonings are discussed, as well as the potential therapeutic use of pralidoxime in organophosphate intoxication.

Aldicarb poisoning by an illicit rodenticide imported into the United States: Tres Pasitos

OBJECTIVE

Although intentional and unintentional rodenticide poisoning is common, most readily available agents are of relatively low acute toxicity. A four-year long epidemic of severe toxicity from rodenticide exposure continues among patients predominantly of Dominican descent living in New York City. This study characterizes the ongoing epidemic of acute cholinesterase inhibitor poisoning due to an illicit rodenticide and identifies its etiology.

METHODS

A prospectively collected case series of poisoned patients referred to the New York City Poison Control Center. The main outcome measures include the clinical characteristics upon presentation, antidotal and other therapeutic requirements, and patient outcome. Product analysis was performed with paper chromatography, gas chromatography/mass spectrometry, and high-performance liquid chromatography. A murine model assessing both clinical effect and cholinesterase activity was also performed.

RESULTS

Thirty-five patients were referred following exposure to Tres Pasitos. Patients developed signs of cholinergic hyperactivity and many required high doses of atropine (>10 mg) to control these symptoms. The source was identified as a rodenticidal compound sold illicitly in local groceries primarily within the Dominican community. Murine cholinesterase activity fell significantly following exposure to the rodenticide. High-performance liquid chromatography identified aldicarb, an extremely potent carbamate-type cholinesterase inhibitor, not licensed for rodenticidal use in this country.

CONCLUSION

Illicit sale of undocumented compounds poses a substantial public health threat. Despite several public health interventions, the epidemic continues.

Modern strategies in therapy of organophosphate poisoning

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

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.