Oximes for acute organophosphate pesticide poisoning

Predictors of Mortality in Hospitalized Patients With Pesticide Poisoning

Background Organophosphorus poisoning (OPP) is a prevalent mortality rate that varies from 2% to 25% method of suicides worldwide. ICUs commonly employ various scoring systems such as the Glasgow Coma Scale (GCS), Acute Physiology and Chronic Health Evaluation II (APACHE II), Simplified Acute Physiology Score II (SAPS II), and International Programme on Chemical Safety (IPCS) Poison Severity Score (PSS) tools for risk stratification for mortality prediction scores and prognosis. This study aims to compare the predictive validity of these systems in hospitalized patients suffering from pesticide poisoning in a teaching hospital located in central India. Methods A prospective study design was utilized to gather relevant variables for calculating the GCS, APACHE II, SAPS II, and IPCS scales in patients affected by pesticide poisoning. Data on the administered doses of atropine and pralidoxime (PAM) were also recorded. Results We have identified several independent predictors of mortality among patients suffering from pesticide poisoning. The GCS (P=0.001), tracheostomy (P=0.001), APACHE II score (P=0.01), and SAPS II score (P=0.001) were all found to be significant indicators of mortality. Interestingly, the GCS demonstrated comparable predictive ability for mortality when compared to the APACHE II (0.82 (95% confidence interval (CI) 0.70 to 0.94)) and SAPS II (0.83 (95% CI 0.72 to 0.94)) scores, with no statistically significant difference (P=0.75) observed. Among the variables used in the IPCS PSS (GCS, heart rate, systolic blood pressure (BP), intubation, and pupil size), only GCS (P=0.05), and intubation (P=0.01) exhibited a significant association with mortality. Conclusions Our study determined that the GCS score, SAPS II, IPCS PSS, and APACHE II exhibited equal efficacy in predicting mortality. Notably, the GCS offered an added advantage due to its simplicity and minimal time requirements compared to the other scales.

Methylene blue can act as an antidote to pesticide poisoning of bumble bee mitochondria

The population of bumble bees and other pollinators has considerably declined worldwide, probably, due to the toxic effect of pesticides used in agriculture. Inexpensive and available antidotes can be one of the solutions for the problem of pesticide toxicity for pollinators. We studied the properties of the thiazine dye Methylene blue (MB) as an antidote against the toxic action of pesticides in the bumble bee mitochondria and found that MB stimulated mitochondrial respiration mediated by Complex I of the electron transport chain (ETC) and increased respiration of the mitochondria treated with mitochondria-targeted (chlorfenapyr, hydramethylnon, pyridaben, tolfenpyrad, and fenazaquin) and non-mitochondrial (deltamethrin, metribuzin, and penconazole) pesticides. MB also restored the mitochondrial membrane potential dissipated by the pesticides affecting the ETC. The mechanism of MB action is most probably related to its ability to shunt electron flow in the mitochondrial ETC.

Safety and Efficacy of New Oximes to Reverse Low Dose Diethyl-Paraoxon-Induced Ventilatory Effects in Rats

Background: Oximes are used in addition to atropine to treat organophosphate poisoning. However, the efficiency of oximes is still a matter of debate. In vitro experiments suggested than new oximes are more potent than the commercial oximes. However, the antidotal activity of new oximes has not been assessed in vivo. Methods: The aim of this work was to assess the safety and efficiency of new oximes compared to pralidoxime in a rat model of diethyl paraoxon-induced non-lethal respiratory toxicity. Results: Safety study of oximes showed no adverse effects on ventilation in rats. KO-33, KO-48, KO-74 oximes did not exhibit significant antidotal effect in vivo. In contrast, KO-27 and BI-6 showed evidence of antidotal activity by normalization of respiratory frequency and respiratory times. KO-27 became inefficient only during the last 30 min of the study. In contrast, pralidoxime demonstrated to be inefficient at 30 min post injection. Inversely, the antidotal activity of BI-6 occurred lately, within the last 90 min post injection. Conclusion: This study showed respiratory safety of new oximes. Regarding, the efficiency, KO-27 revealed to be a rapid acting antidote toward diethylparaoxon-induced respiratory toxicity, meanwhile BI-6 was a late-acting antidote. Simultaneous administration of these two oximes might result in a complete and prolonged antidotal efficiency.

High Dose of Pralidoxime Reverses Paraoxon-Induced Respiratory Toxicity in Mice

Objective

The efficiency of pralidoxime in the treatment of human organophosphates poisoning is still unclear. In a rat model, we showed that pralidoxime induced a complete but concentration-dependent reversal of paraoxon-induced respiratory toxicity. The aim of this study was to assess the efficiency of pralidoxime in a species other than rats.

Methods

A dose of diethylparaoxon corresponding to 50% of the median lethal dose was administered subcutaneously to male F1B6D2 mice. Ascending single pralidoxime doses of 10, 50-100 and 150 mg kg^-1 were administered intramuscularly 30 min after diethylparaoxon administration. Ventilation at rest was assessed using whole-body plethysmography and mice temperature was assessed using infrared telemetry. Results are expressed as mean±SE. Statistical analysis used non-parametric tests.

Results

From 30 to 150 min post-injection, diethylparaoxon induced clinical symptoms and a decrease in respiratory frequency, which resulted from an increase in expiratory and inspiratory times associated with an increase in the tidal volume. In the 10-, 50- and 100-mg kg^-1 pralidoxime groups, there was a trend towards a non-significant improvement of paraoxon-induced respiratory toxicity. The 150 mg kg^-1 dose of pralidoxime induced a significant reversal of all respiratory parameters.

Conclusion

In the present study, a toxic but non-lethal model of diethylparaoxon in awake, unrestrained mice was observed. By administering an equipotent dose of diethylparaoxon to rats, a 150 mg kg^-1 dose of pralidoxime administered alone completely reversed diethylparaoxon-induced respiratory toxicity in mice. The dose dependency of reversal suggests that further studies are needed for assessing plasma concentrations of pralidoxime resulting in reversal of toxicity.

Mitigation of diazinon-induced cardiovascular and renal dysfunction by gallic acid

Studies of the link between environmental pollutants and cardiovascular dysfunction, neglected for decades, have recently provided new insights into the pathology and consequences of these killers. In this study, rats were divided into four groups, each containing 10 rats. The rats in group one served as controls and were administered normal saline, whereas the rats in group two were orally gavaged with 3 mg/kg of diazinon (DZN) alone for twenty one consecutive days. The rats in groups 3 and 4 were administered respective 60 mg/kg and 120 mg/kg gallic acid (GA) in addition to DZN for twenty one consecutive days. Exposure of rats to diazinon significantly (p<0.05) reduced the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and reduced glutathione (GSH) content. Malondialdehyde, hydrogen peroxide (H2O2) and nitric oxide (NO) contents were also significantly (p<0.05) elevated following DZN exposure. DZN further caused a significant (p<0.05) decrease of heart rate and QT interval prolongation. Hematologic analysis revealed significant reduction (p<0.05) in packed cell volume (PCV), hemoglobin concentration (Hb), red blood cell (RBC) count, and total white blood cell count of rats administered only DZN. Observations in this study suggest a modulatory role of gallic acid in diazinon-induced anemia and associated cardiovascular dysfunction in rats. Treatment with gallic acid reversed the oxidative stress markers studied, increased the antioxidant defence system and reduced deleterious effects on hematological parameters in rats. Pathologic findings of the heart and kidney were also found to be lessened.

Reactivation of plasma butyrylcholinesterase by pralidoxime chloride in patients poisoned by WHO class II toxicity organophosphorus insecticides

Some clinicians assess the efficacy of pralidoxime in organophosphorus (OP) poisoned patients by measuring reactivation of butyrylcholinesterase (BuChE). However, the degree of BuChE inhibition varies by OP insecticide, and it is unclear how well oximes reactivate BuChE in vivo. We aimed to assess the usefulness of BuChE activity to monitor pralidoxime treatment by studying its reactivation after pralidoxime administration to patients with laboratory-proven World Health Organization (WHO) class II OP insecticide poisoning. Patient data were derived from 2 studies, a cohort study (using a bolus treatment of 1g pralidoxime chloride) and a randomized controlled trial (RCT) (comparing 2g pralidoxime over 20min, followed by an infusion of 0.5g/h, with placebo). Two grams of pralidoxime variably reactivated BuChE in patients poisoned by 2 diethyl OP insecticides, chlorpyrifos and quinalphos; however, unlike acetylcholinesterase reactivation, this reactivation was not sustained. It did not reactivate BuChE inhibited by the dimethyl OPs dimethoate or fenthion. The 1-g dose produced no reactivation. Pralidoxime produced variable reactivation of BuChE in WHO class II OP-poisoned patients according to the pralidoxime dose administered, OP ingested, and individual patient. The use of BuChE assays for monitoring the effect of pralidoxime treatment is unlikely to be clinically useful.

A prospective observational study on different poisoning cases and their outcomes in a tertiary care hospital

Objectives:

Poisonings and snake bites constitute major health-care problems worldwide. This observational study was conducted to identify factors associated with outcomes in such cases and to suggest strategies to improve them.

Methods:

This is a prospective study conducted in the emergency medicine department of a tertiary care hospital. The study included 102 poisoning and 64 snake bite cases. Data regarding demographics, mode of poisoning, lag time in treatment, first aid, outside and indoor treatment, co-morbid illness, duration of hospitalisation and final outcome were collected in a prestructured proforma.

Results:

The age of the patients ranged from 11 to 68 years and incidence was more common among males (69.9%) compared to females (30.1%). The major types of poisonings included organophosphorus compounds (16.3%), aluminium phosphide (12%), drug overdose (10.8%) and corrosives (6%). There were 18 (18.6%) and 1 (1.6%) deaths in poisoning and snake bite cases, respectively. In poisoning cases, the duration of hospitalisation was significantly decreased if patient received outside treatment (p = 0.02) and if he or she had lesser lag time in reaching the hospital (p = 0.009).

Conclusions:

Measures to reduce lag time and provide immediate treatment at initial encounter may be effective in reducing duration of hospitalisation and possibly mortality in poisoning and snake bite cases.

Repeated pulse intramuscular injection of pralidoxime chloride in severe acute organophosphorus pesticide poisoning

OBJECTIVE

This study aimed to clarify the efficacy of 2 therapies for patients with severe acute organophosphorus pesticide poisoning, including atropine adverse effects, the length of intensive care unit (ICU) stay, complications, and mortality.

METHODS

A retrospective cohort study of 152 cases collected from May 2008 to November 2012 at 2 urban university hospitals was conducted. Patients admitted to the hospital for organophosphate poisoning were divided into 2 groups with different therapeutic regimens: group A was administered a repeated pulse intramuscular injection of pralidoxime chloride, and group B received the same initial dosage of atropine and pralidoxime chloride, but pralidoxime chloride intravenous therapy was administered for only 3 days, regardless of the length of atropine therapy. Subsequently, atropine adverse effects, length of ICU stay, complications, and mortality were statistically analyzed and compared between the 2 groups.

RESULTS

The total dose of atropine was 57.40 ± 15.14 mg in group A and 308.26 ± 139.16 mg in group B; group A received less atropine than did group B (P = .001). The length of ICU stay in group A was reduced (P = .025), and group A had fewer atropine adverse effects (P = .002). However, there was no significant difference in the mortality or complication rate between the 2 groups (P > .05).

CONCLUSION

In patients with severe poisoning, group A used less atropine, had fewer atropine adverse effects, and had a shorter ICU stay. We suggest that therapy should be started as early as possible using a sufficient amount of pralidoxime chloride started intramuscularly in combination with atropine and that the drugs should not be prematurely discontinued.

Interference by pralidoxime (PAM) salts in clinical laboratory tests

BACKGROUND

Drugs sometimes alter the results of clinical laboratory tests. We examined the effects of pralidoxime (PAM) salts, a medicine used to treat organophosphorus poisoning, on clinical laboratory test results for the first time.

METHODS

The effects of PAM salts on glucose (GLU) measurements were examined using a point-of-care testing (POCT) meter, four self-monitoring of blood glucose (SMBG) meters, and two biochemical autoanalyzers. The effects of PAM salts on other clinical tests were also evaluated.

RESULTS

The addition of PAM iodide or potassium iodide, but not of PAM chloride or potassium chloride, to blood samples increased the GLU values measured by one POCT meter and 4 SMBG meters using the enzyme electrode (hydrogen peroxidase or oxygen electrode) method. On the other hand, PAM iodide or PAM chloride, but not KI or KCl, affected the values measured at 340 nm by an autoanalyzer using absorption spectrophotometry in 8 of 14 clinical laboratory tests. The absorption spectrum of PAM changed from 294 to 338 nm due to the reaction between PAM and the alkaline buffer, a component of the measuring reagents.

CONCLUSIONS

PAM iodide increases the GLU values measured by the enzyme electrode method, and PAM salts affected the values measured at 340 nm by absorption spectrophotometry in many other clinical test items.

Cholinergic stimulation of the immune system protects against lethal infection by Salmonella enterica serovar Typhimurium

SUMMARY

The cholinergic nervous system has been demonstrated to attenuate the inflammatory response during sepsis via the inhibitory action of acetylcholine (ACh) on macrophages. These findings were largely based on experimental sepsis models using endotoxin as the inducing agent. Herein, however, we report that the specific inhibition of acetylcholinesterase (AChE) renders animals more resistant to infection by a virulent strain of Salmonella enterica serovar Typhimurium, a Gram-negative enteric pathogen. Inhibition of AChE was induced by a subchronic exposure to paraoxon, a potent anti-cholinesterase metabolite of the organophosphorous compound parathion. Our findings indicate that inhibition of AChE enhanced survival of infected mice in a dose-dependent fashion and this correlated with efficient control of bacterial proliferation in target organs. Immunologically, inhibition of AChE enabled the animals to mount a more effective inflammatory anti-microbial response, and to secrete higher levels of interleukin-12, a key T helper type 1-promoting cytokine. The ACh-induced enhancement in resistance to infection was abrogated by co-administration of an oxime which can reactivate AChE. Hence, in a model of Gram-negative bacterial infection, cholinergic stimulation is shown to enhance the anti-microbial immune response leading to effective control of bacterial proliferation and enhanced animal survival.

Evidence for perinatal and child health care guidelines in crisis settings: can Cochrane help?

BACKGROUND

It is important that healthcare provided in crisis settings is based on the best available research evidence. We reviewed guidelines for child and perinatal health care in crisis situations to determine whether they were based on research evidence, whether Cochrane systematic reviews were available in the clinical areas addressed by these guidelines and whether summaries of these reviews were provided in Evidence Aid.

METHODS

Broad internet searches were undertaken to identify relevant guidelines. Guidelines were appraised using AGREE and the clinical areas that were relevant to perinatal or child health were extracted. We searched The Cochrane Database of Systematic Reviews to identify potentially relevant reviews. For each review we determined how many trials were included, and how many were conducted in resource-limited settings.

RESULTS

Six guidelines met selection criteria. None of the included guidelines were clearly based on research evidence. 198 Cochrane reviews were potentially relevant to the guidelines. These reviews predominantly addressed nutrient supplementation, breastfeeding, malaria, maternal hypertension, premature labour and prevention of HIV transmission. Most reviews included studies from developing settings. However for large portions of the guidelines, particularly health services delivery, there were no relevant reviews. Only 18 (9.1%) reviews have summaries in Evidence Aid.

CONCLUSIONS

We did not identify any evidence-based guidelines for perinatal and child health care in disaster settings. We found many Cochrane reviews that could contribute to the evidence-base supporting future guidelines. However there are important issues to be addressed in terms of the relevance of the available reviews and increasing the number of reviews addressing health care delivery.

Organophosphate poisoning due to a wheat bagel

OBJECTIVE

Organophosphate compounds are possibly the most widely-used insecticides worldwide. Organophosphate compounds cause poisoning, inhibiting acetylcholinesterase at the cholinergic synapses. Civilian casualties resulted from a terrorist attack with sarin in a Tokyo subway. Recent terrorist activities have also raised concerns that organophosphate or nerve agents may be used as a weapon of terror or mass destruction.

METHODS

In this study, an extraordinary type of mass poisoning was evaluated. Especially by focusing on the way of poisoning, the demographic features and clinical findings of patients were analyzed.

RESULTS

After eating a wheat bagel, 13 patients with organophosphate poisoning were admitted to our emergency department. Seven were males and 6 were females. The mean age of the patients was 26 +/- 13.9. The mean serum acetylcholinesterase level was 2945.1+/-2648.9 U/L. Nine patients who had supportive treatment and who were given atropine and pralidoxime were hospitalized approximately 6.8+/-6.5 days. All of the patients recovered after the treatment and no deaths occurred.

CONCLUSION

If organophosphate poisoning is not diagnosed and treated in time, it may be fatal. When cases of food poisoning are admitted to the hospital, attention must be taken especially if it is a mass poisoning.

Eight new bispyridinium oximes in comparison with the conventional oximes pralidoxime and obidoxime: in vivo efficacy to protect from diisopropylfluorophosphate toxicity

In search for more efficacious reactivators of acetylcholinesterase (AChE) inhibited by organophosphorus compounds, experimental K-oximes have been synthesized which show good in vitro efficacy. However, AChE inhibition by oximes themselves (as quantified by their intrinsic IC50) is the major cause of oxime toxicity and the dose-limiting factor. To assess K-oxime efficacy in vivo, the extent of protection from mortality induced by diisopropylfluorophosphate (DFP) was quantified by Cox survival analysis and compared with that of the clinically available oximes. Oximes were administered in an equitoxic dosage, i.e. half the LD01. Best protection was conferred by K-27, reducing the relative risk of death (RR) to 16% of control RR (P < or = 0.05), which was statistically significantly better (P < or = 0.05) than all other tested oximes, except obidoxime, K-53 and K-75. The efficacy of obidoxime (RR = 0.19), K-48 (RR = 0.28), K-53 (RR = 0.22), K-74 (RR = 0.38) and K-75 (RR = 0.29) was significantly (P < or = 0.05) better than that of 2-PAM (RR = 0.62) and K-113 (RR = 0.73). No significant protective effect was observed for K-107 and K-108. Our LD50 data show that K-107, K-108 and K-113 (which strongly inhibit AChE in vitro) are in vivo markedly more toxic than all other oximes tested and can therefore only be safely administered at a low dosage which is insufficient to protect from DFP-induced mortality. Dosage calculations based on in vitro IC50 measurements may therefore in future replace in vivo LD50 determinations, thereby reducing the number of animals required.

Comparison of two commonly practiced atropinization regimens in acute organophosphorus and carbamate poisoning, doubling doses vs. ad hoc: a prospective observational study

There is a wide variation and lack of evidence in current recommendations for atropine dosing schedules leading to subsequent variation in clinical practice. Therefore, we sought to examine the safety and effectiveness of a titrated vs. ad hoc atropine treatment regimen in a cohort of patients with acute cholinesterase inhibitor pesticide poisoning. A prospective cohort study was conducted in three district secondary referral hospitals in Sri Lanka using a structured data collection form that collected details of clinical symptoms and outcomes of cholinesterase inhibitor pesticide poisoning, atropine doses, and signs of atropinization. We compared two hospitals that used a titrated dosing protocol based on a structured monitoring sheet for atropine infusion with another hospital using an ad hoc regime. During the study, 272 symptomatic patients with anticholinesterase poisoning requiring atropine were admitted to the three hospitals. Outcomes of death and ventilation were analyzed for all patients, 226 patients were prospectively assessed for atropine toxicity. At baseline, patients in the titrated dose cohort had clinical signs consistent with greater toxicity. This in part may be due to ingestion of more toxic organophosphates. They received less pralidoxime and atropine, and were less likely to develop features of atropine toxicity, such as delirium (1% vs. 17%), hallucinations (1% vs. 35%), or either (1% vs. 35%) and need for patient restraint (3% vs. 48%) compared with the ad hoc dose regime. After adjusting for the pesticides ingested, there was no difference in mortality and ventilatory rates between protocols. Ad hoc high dose atropine regimens are associated with more frequent atropine toxicity without any obvious improvement in patient outcome compared with doses titrated to clinical effect. Atropine doses should be titrated against response and toxicity. Further education and the use of a structured monitoring sheet may assist in more appropriate atropine use in anticholinesterase pesticide poisoning.

Toxicology in the critical care unit

Toxicologic conditions are encountered in critically ill patients due to intentional or unintentional misuse of or exposure to therapeutic or illicit drugs. Additionally, toxicities related to medical interventions may develop in hospitalized patients. This review focuses on recent developments in the field of critical care toxicology. Early interventions to decrease absorption or enhance elimination of toxins have limited value. Specific interventions to manage toxicities due to analgesics, sedative-hypnotics, antidepressants, antipsychotics, cardiovascular agents, alcohols, carbon monoxide, and cholinergic agents are reviewed. Hospital-acquired toxicities due to methemoglobinemia, propylene glycol, and propofol should be recognized and treated. The clinician is continually required to incorporate clinical judgment along with available scientific data and clinical evidence to determine the best therapy for toxicologic conditions.

Management of acute organophosphorus pesticide poisoning

Organophosphorus pesticide self-poisoning is an important clinical problem in rural regions of the developing world, and kills an estimated 200,000 people every year. Unintentional poisoning kills far fewer people but is a problem in places where highly toxic organophosphorus pesticides are available. Medical management is difficult, with case fatality generally more than 15%. We describe the limited evidence that can guide therapy and the factors that should be considered when designing further clinical studies. 50 years after first use, we still do not know how the core treatments--atropine, oximes, and diazepam--should best be given. Important constraints in the collection of useful data have included the late recognition of great variability in activity and action of the individual pesticides, and the care needed cholinesterase assays for results to be comparable between studies. However, consensus suggests that early resuscitation with atropine, oxygen, respiratory support, and fluids is needed to improve oxygen delivery to tissues. The role of oximes is not completely clear; they might benefit only patients poisoned by specific pesticides or patients with moderate poisoning. Small studies suggest benefit from new treatments such as magnesium sulphate, but much larger trials are needed. Gastric lavage could have a role but should only be undertaken once the patient is stable. Randomised controlled trials are underway in rural Asia to assess the effectiveness of these therapies. However, some organophosphorus pesticides might prove very difficult to treat with current therapies, such that bans on particular pesticides could be the only method to substantially reduce the case fatality after poisoning. Improved medical management of organophosphorus poisoning should result in a reduction in worldwide deaths from suicide.

Organophosphate poisoning: 10 years of experience in southern Taiwan

Poisoning due to organophosphate pesticides is an important cause of morbidity and mortality worldwide. Although standard treatments involving the administration of atropine and oximes have been used, there remain many controversial areas concerning organophosphate poisoning (OPP). Herein, we present our 10 years of experience in assessing the severity of OPP in southern Taiwan. A retrospective study was performed on patients admitted with OPP. A total of 75 patients (50 males and 25 females) were studied between January 1996 and December 2005. Diagnosis was based on a clinical assessment and serum acetylcholinesterase (AChE) level at the time of hospital admission. The severity of OPP was assessed using the grading system of Bardin et al. The duration and dosage of atropine and palidroxime were recorded. All the biochemical data were analyzed. Sixty-one of the patients had attempted suicide and 14 patients had accidental exposure. The overall mortality rate was 8%. Muscarinic effects were observed in 66 (88%) of the OPP patients and the most frequent symptom was bronchial hypersecretion (52%). Among these three different severity groups, prolonged length of stay, higher infection rates, and higher mortality were found in the life-threatened group. The initial serum C-reactive protein (CRP) level was strongly correlated to the severity grading of the OPP. Nearly half of the patients were admitted to the intensive care unit (ICU) and, of this, 21 patients developed respiratory failure within 72 hours. Low serum AChE levels support the diagnosis of OPP, but no significant association was found between the severity of OPP and serum AChE levels. The grading system of Bardin et al is very helpful for physicians to facilitate the recognition of seriously poisoned subjects, and to permit their early admission to an ICU. Initial serum CRP, an acute phase reactant, had significant value in assessing the severity of the OPP. Although the management of acute OPP is supportive and the recovery rate is high, anti-cholinergic therapy should be used as soon as possible to counteract muscarinic effects. Physicians must be aware of the potential dangers of respiratory failure, which could occur within 72 hours of OPP.

Development of antidotes: Problems and strategies

Antidotes against chemical warfare agents are "orphan drugs" given that these poisonings are rare. Therefore, they are of limited interest to the pharmaceutical industry. For this reason, and recognizing the increasing threat of terrorist or asymmetrical use of chemical warfare agents, the responsibility for research into medical countermeasures against these weapons is of primary interest to armies. Accordingly, the research activities of the Bundeswehr Institute of Pharmacology and Toxicology are dedicated to improving diagnosis, prophylaxis and therapy of individuals who are exposed to a chemical agent. Here, antidote development and testing are a high priority in the research program, particularly with respect to organophosphorus (OP) nerve agents and sulphur mustard. The Institute has been coordinating research activities undertaken in house and in collaboration with external researchers. The research program aims to develop primarily in vitro models to minimize the sacrifice of animals, using strategies, which involve human material early in antidote testing. An animal model using isolated mouse diaphragm demonstrated the correlation between AChE activity and neuromuscular function. A similar relationship was found between erythrocyte AChE and neuromuscular function in patients with acute OP pesticide poisoning. In vitro rate constants of the various reactions that are involved in enzyme inhibition and reactivation using human material were used for prediction of what would happen in vivo. This prediction could be confirmed in a patient with acute OP pesticide poisoning. Finally, computer models are being established to estimate the therapeutic effect of an antidote in various human poisoning scenarios. This approach is necessary to compensate for the lack of human clinical pharmacodynamic studies that are usually required for drug regulatory approval, given the obvious ethical issues preventing human volunteer studies with these agents.

Toxicity due to organophosphorus compounds: what about chronic exposure?

The inappropriate use of toxic chemicals is common in developing countries, where it leads to excessive exposure and high risks of unintentional poisoning. The risks are particularly high with the pesticides used in agriculture, where poor rural populations live and work in close proximity to these compounds, which are often stored in and around the home. It is estimated that 99% of all deaths from pesticide poisoning occur in developing countries. Whilst the acute toxicity of pesticides has been well documented, there is still relatively little known of the effects on health of chronic pesticide exposure. Organophosphate insecticides have been extensively used in agriculture in developing countries, with little protection for the communities and individuals thus exposed. Given the indisputable chronic exposure of vulnerable groups to organophosphate compounds, including pregnant women, the fetus and young children, the potential for widespread adverse effects is considerable. Thus, whilst there is some evidence that chronic exposure may have adverse effects on health, there is an urgent need for high-quality observational and interventional studies of both occupational and environmental exposure to these compounds.

Alkalinisation for organophosphorus pesticide poisoning

BACKGROUND

Poisoning with organophosphorus pesticides (OPs) is an important cause of morbidity and mortality in all parts of the world, particularly developing countries. The case-fatality ratio for pesticide intentional self-poisoning is around 10-20% even when the standard antidotes (atropine, oximes and benzodiazepines) are used. Alternative treatments have been trialled in an attempt to improve outcomes from acute OP poisoning, one of which is plasma alkalinisation. Animal and preliminary human research has suggested benefit from plasma alkalinisation with sodium bicarbonate (NaHCO3) as a treatment for acute OP poisoning.

OBJECTIVES

To determine the efficacy of alkalinisation, in particular NaHCO3, for the treatment of acute OP poisoning.

SEARCH STRATEGY

We searched MEDLINE (1966-2004), EMBASE (1980-2004), the Controlled Trials Register of the Cochrane Collaboration, Current Awareness in Clinical Toxicology, Info Trac, http://www.google.com.au, and Science Citation Index of studies identified by the previous searches. We also manually reviewed the bibliographies of identified articles and personally contacted experts in the field.

SELECTION CRITERIA

Randomised controlled trials and controlled clinical trials of symptomatic patients following acute OP poisoning treated with alkalinisation. The quality of studies and eligibility for inclusion was assessed using criteria by Jadad and Schulz.

DATA COLLECTION AND ANALYSIS

Studies were identified and both authors independently extracted data which was recorded on a pre-designed form. Study design, including the method of randomisation, participant characteristics, type of intervention and outcomes were recorded. Outcomes were discussed, but unfortunately specific analyses could not be performed, given the poor quality of the studies identified.

MAIN RESULTS

Five studies were identified but none satisfied inclusion criteria. NaHCO3 was used in each of these to induce alkalinisation. Two studies were uncontrolled, two studies were historically controlled and one study was randomised but poorly concealed. Marked heterogeneity between subjects and treatments was noted - for example, a different regimen of NaHCO3 was used in each study. While there may have been a trend towards improved outcomes (lower total dose of atropine and shorter length of stay), these were not statistically significant.

AUTHORS' CONCLUSIONS

There is insufficient evidence to support the routine use of plasma alkalinisation for treatment of OP poisoning. Further research is required to determine the method of alkalinisation that will optimise outcomes, and the regimen which will produce the target arterial pH of 7.50 (range 7.45-7.55). This should be followed by a well-designed randomised controlled trial to determine efficacy.