Prolonged toxicity of organophosphate poisoning

Serial Serum Cholinesterase Activities as a Prognostic Factor in Organophosphate Poisoned Patients

Objective

Organophosphate poisoning is a serious clinical entity and of considerable morbidity and mortality. Several factors have been identified to predict outcomes of organophosphate poisoning. This investigation aims to identify the relationship between the dynamics of serum cholinesterase (SChE) activity and mortality.

Methods

In this retrospective study, medical records of all patients with acute organophosphate poisoning were reviewed from January 2001 to December 2009. Clinical features, SChE activity, Glasgow Coma Scale, laboratory findings, electrocardiogram finding, management and their outcomes were examined.

Results

A total of 169 patients were included in this study. A total of 55 patients were enrolled. Deceased patients were 8 in number. Absence of an increase in SChE activity was related with mortality in organophosphate poisoned patients (p value=0.036; odds ratio, 5.445; 95% confidence interval, 1.121-26.551).

Conclusions

The absence of an increase in SChE activity is associated with higher mortality in organophosphate poisoning. The SChE dynamic activity can provide a guide to physicians in the evaluation and management of organophosphate poisoned patients.

Clinical Toxicology of Insecticides

Some insects compete for our food, some damage construction materials and some are important disease vectors in humans and animals. Hence, it is not surprising that chemicals (insecticides) have been developed that kill insects and other arthropods. More recently introduced insecticides, such as the neonicotinoids, have been produced with the intent that humans and animals will not be harmed by their appropriate use. This chapter reviews the clinical features and management of exposure to organophosphorus (OP) and carbamate insecticides, neonicotinoids, phosphides and pyrethroids. In the developing world where the ambient temperature is often high and personal protection equipment often not worn, poisoning particularly from OP and carbamate insecticides is common in an occupational setting, though more severe cases are due to deliberate ingestion of these pesticides. Both of these insecticides produce the cholinergic syndrome. The neonicotinoids, a major new class of insecticide, were introduced on the basis that they were highly specific for subtypes of nicotinic receptors that occur only in insect tissues. However, deliberate ingestion of substantial amounts of a neonicotinoid has resulted in features similar to those found in nicotine (and OP and carbamate) poisoning, though the solvent in some formulations may have contributed to their toxicity. Phosphides interact with moisture in air (or with water or acid) to liberate phosphine, which is the active pesticide. Inhalation of phosphine, however, is a much less frequent cause of human poisoning than ingestion of a metal phosphide, though the toxicity by the oral route is also due to phosphine liberated by contact of the phosphide with gut fluids. It is then absorbed through the alimentary mucosa and distributed to tissues where it depresses mitochondrial respiration by inhibiting cytochrome c oxidase and other enzymes. Dermal exposure to pyrethroids may result in paraesthesiae, but systemic toxicity usually only occurs after ingestion, when irritation of the gastrointestinal tract and CNS toxicity, predominantly coma and convulsions, result.

Prolonged cholinergic crisis and compartment syndrome following subcutaneous injection of an organophosphate compound for suicide attempt

A case of poisoning with highly lipid soluble organophosphate compound, fenthion is reported in which cholinergic crisis recurred upto 25 days following a suicide attempt. Subcutaneous injection of fenthion in the antecubital fossa by the patient produced massive swelling, cellulitis and compartment syndrome of the left arm. Emergency fasciotomy helped in restoration of circulation and saved the limb from being amputated.

Is there a relationship between the blood cholinesterase and QTc interval in the patients with acute organophosphate poisoning?

Organophosphates cause poisoning as a result of the excessive accumulation of acetylcholine at the cholinergic synapses due to inhibition of acetylcholinesterase (ChE). In the literature, it has been reported that there have been electrocardiographic abnormalities, including QT-interval prolongation in most patients with acute organophosphate poisoning (OPP), and a relation between blood ChE level and clinical severity in acute OPP. The aim of this study is to assess the relationship between blood ChE level and QTc interval in the patients with acute OPP. This retrospective study consists of 20 patients admitted to the emergency intensive care unit. A total of 93 QTc interval and blood ChE measures obtained on the same day from 20 cases were compared for their correlation. There were prolonged QTc intervals in 35.4% of the ECGs. There was a negative correlation between QTc interval and blood ChE measures. In following up the patients with acute OPP, QTc interval may be useful when blood ChE levels are low and may provide complementary information concerning the severity of poisoning. However, further prospective studies, supporting the present results, are needed.

The role of diazepam in the treatment of nerve agent poisoning in a civilian population

The main site of action of diazepam, as with other benzodiazepines, is at the GABA(A) receptor, although it has been suggested that some of the potentially beneficial actions of diazepam in nerve agent poisoning are mediated through other means. It is likely that convulsions may have long-term sequelae in the central nervous system, because of damage by anoxia and/or excitotoxicity. Numerous pharmacodynamic studies of the action of diazepam in animals experimentally poisoned with nerve agents have been undertaken. In nearly all of these, diazepam has been studied in combination with other antidotes, such as atropine and/or pyridinium oximes, sometimes in combination with pyridostigmine pretreatment. These studies show that diazepam is an efficacious anticonvulsant in nerve agent poisoning. There is considerable experimental evidence to support the hypothesis that diazepam (and other anticonvulsants) may prevent structural damage to the central nervous system as evidenced by neuropathological changes such as neuronal necrosis at autopsy. In instances of nerve agent poisoning during terrorist use in Japan, diazepam seems to have been an effective anticonvulsant. Consequently, the use of diazepam is an important part of the treatment regimen of nerve agent poisoning, the aim being to prevent convulsions or reduce their duration. Diazepam should be given to patients poisoned with nerve agents whenever convulsions or muscle fasciculation are present. In severe poisoning, diazepam administration should be considered even before these complications occur. Diazepam is also useful as an anxiolytic in those exposed to nerve agents.

Suicide and exposure to organophosphate insecticides: cause or effect?

BACKGROUND

Suicide using pesticides as agent is recognized as a major cause of pesticide poisoning.

METHODS

A literature review of mortality and morbidity studies related to suicide among pesticide-exposed populations, and of human and animal studies of central nervous system toxicity related to organophosphate (OP) pesticides was performed.

RESULTS

Suicide rates are high in farming populations. Animal studies link OP exposure to serotonin disturbances in the central nervous system, which are implicated in depression and suicide in humans. Epidemiological studies conclude that acute and chronic OP exposure is associated with affective disorders. Case series and ecological studies also support a causal association between OP use and suicide.

CONCLUSIONS

OPs are not only agents for suicide. They may be part of the causal pathway. Emphasizing OPs solely as agents for suicide shifts responsibility for prevention to the individual, reducing corporate responsibility and limiting policy options available for control.

Diazepam in the treatment of organophosphorus ester pesticide poisoning

Although the main site of action of diazepam, as with other benzodiazepines, is at the gamma-aminobutyric acid A (GABAA) receptor, the degree to which the beneficial actions of diazepam in organophosphorus (OP) ester pesticide poisoning are mediated through the GABAA receptor has been a matter of controversy. Although in most series of OP intoxications, convulsions have been relatively uncommon, it is probable that convulsions produce long-term sequelae in the central nervous system by causing structural damage. Animal studies have demonstrated that diazepam prevents and treats convulsions produced by OPs and may prevent the late effects caused by damage to the central nervous system induced by such convulsions. Consequently, the use of diazepam is an important part of the treatment regimen of severe OP poisoning as it prevents, or at least reduces the duration of, convulsions. In addition, case reports suggest that diazepam will also ameliorate muscle fasciculation, a subjectively unpleasant feature of OP pesticide poisoning. There are no data, either experimental or clinical, demonstrating any clear effect of diazepam alone on lethality in OP poisoning. In fact, in one study of large animals, diazepam, given alone, increased lethality. In animals experimentally poisoned with OPs, combined treatment with atropine and diazepam significantly lowered lethality compared with atropine treatment alone, indicating a clear beneficial effect. There are numerous case reports of the use of diazepam, generally as an adjunct to other more specific OP antidotes such as atropine and/or pyridinium oximes. Based on this evidence and pharmacodynamic studies in experimental animals, diazepam should be given to patients poisoned with OPs whenever convulsions or pronounced muscle fasciculation are present. In severe poisoning, diazepam administration should be considered even before these complications develop. Although diazepam has a large therapeutic index, there appears to be no place for its routine use in OP poisoning. Diazepam should be given intravenously to patients treated in hospital for OP poisoning, although the intramuscular route is used to administer diazepam outside hospital, such as on the battlefield, when an auto-injector is employed. It should be recognised, however, that absorption by the intramuscular route is poor.

Protective equipment for health care facility decontamination personnel: regulations, risks, and recommendations

After recent terrorist attacks, new attention has been focused on health care facility decontamination practices. This article reviews core issues related to the selection of appropriate personal protective equipment for health care facility decontamination personnel, with an emphasis on respiratory protection. Existing federal regulations focus primarily on scene response and not on issues specific to health care facility decontamination practices. Review of existing databases, relevant published literature, and individual case reports reveal some provider health risks, especially when the exposure involves organophosphate agents. However, reported risks from secondary exposure to contaminated patients at health care facilities are low. These risks should be adequately addressed with Level C personal protective equipment, including air-purifying respirator technologies, unless the facility determines that specific local threats require increased levels of protection.

Serum acetylcholinesterase and prognosis of acute organophosphate poisoning

OBJECTIVE

The aim of this study is to investigate the prognostic value of serum acetylcholinesterase levels and their relationship with neurological syndromes (Type 1 syndrome, intermediate syndrome, and delayed polyneuropathy) in acute organophosphate poisoning.

MATERIALS AND METHODS

Thirty-two consecutive patients with acute organophosphate poisoning admitted to the Ondokuz Mayis University Emergency Department from June 1999 to January 2001 were evaluated. Patients were assessed according to admission time, symptoms, and results of clinical exams and their serum acetylcholinesterase levels were determined on days 1, 2, 3, 7, and the last day.

RESULTS

There was no significant difference between the first-day serum acetylcholinesterase of the patients with severe poisoning (n = 22, 68.75%) and of the patients with mild poisoning (n = 10, 31.25%; NS). There was no discernible difference between the serum acetylcholinesterase obtained on days 1 and 3 after poisoning from the patients with intermediate syndrome (n = 5, 15.6%; means: 0.90 +/- 0.65 vs. 0.88 +/- 0.53, 19.35 vs. 18.92%; NS, sensitivity = 80%; specificity = 87.5%). There was a significant difference between the serum acetylcholinesterase obtained on days 1 and 3 from the patients with nonintermediate syndrome (n = 24, 75%; means: 1.05 +/- 0.24 vs. 1.68 +/- 0.29, 22.58 vs. 36.12%; p < 0.001). There was no discernible significant difference in serum acetylcholinesterase between the patients with organophosphorus-induced delayed polyneuropathy (n = 7, 21.8%) and nonorganophosphorus-induced delayed polyneuropathy. In the patients who died (n = 5, 15.6%), serum acetylcholinesterase showed no discernible increase day 1-the last day (means: 0.50 +/- 0.25 vs. 0.46 +/- 0.26, 10.75 vs. 9.89%; NS). There was a significant difference between the serum acetylcholinesterase levels obtained on days 1 and the last day from the patients who survived (n = 27, 84.3%; means: 1.14 +/- 0.25 vs. 2.32 +/- 0.26, 24.51 vs. 49.89%; p < 0.001).

CONCLUSION

In the acute phase of organophosphate poisoning, low serum acetylcholinesterase (> 50% of minimum normal value) supports the diagnosis of organophosphate poisoning but it does not show a significant relationship to the severity of poisoning (NS). The serum acetylcholinesterase activity may be a useful parameter in following the acute prognosis of organophosphate poisoning.

Delayed toxidromes

Some toxins do not result in clinical manifestations until several hours after exposure. This article reviews those agents that may cause delayed-onset toxicity. They are organized into four classes: specific pharmaceuticals, biologicals, pharmaceutical dosage forms, and chemicals. There are five basic mechanisms for delayed toxicity: delayed absorption, distribution factors, metabolic factors, cellular and organ capacity effects, and unknown. Scientific evidence for delayed-onset of effects varies considerably among the individual toxins.

Clinical and sociodemographic features of acute carbamate and organophosphate poisoning: a study of 70 adult patients in north Jordan

OBJECTIVE

To define the sociodemographic and clinical aspects of organic phosphate and carbamate poisoning.

DESIGN

The records of 70 adults (33 males and 37 females) with carbamate or organophosphate intoxication admitted to a North Jordan Teaching Hospital over a five-year period were reviewed retrospectively. These patients represented 10% of all drug overdoses admitted over the same period.

RESULTS

The most cases occurred in the 15-19 year-old age group and the female to male ratio was 1.1:1. Carbamate intoxication was more than twice as common as organophosphate intoxication. Two thirds (64%) of the patients intended to commit suicide, 26% were due to accidental ingestion and the remaining 10% were from occupational exposure. Muscarinic manifestations were the predominant clinical feature followed by central nervous system and then nicotinic manifestations. Low grade fever, not related to infection, was observed in 49% of the patients and respiratory difficulty in 47%, of which 11% required assisted ventilation. Twenty-nine percent of the patients presented with coma. Three patients died for a hospital mortality of 4%.

CONCLUSIONS

The widespread use of carbamates and organophosphates as household pesticides and the lack of adequate regulations controlling their sale and application has encouraged teenagers to prefer them as a modality of attempted suicide. This source of poisoning has become a major health problem in some developing countries.

Prognostic value of serum cholinesterase in organophosphate poisoning

OBJECTIVE

To determine whether serum cholinesterase level has a prognostic value in human acute organophosphorus poisoning.

DESIGN

Cohort (prospective) prognosis study.

SETTING

Medical ICU at University Hospital.

PATIENTS

Thirty consecutive patients admitted to the ICU for acute organophosphate poisoning.

MEASUREMENTS

Serum cholinesterase level was measured in all patients at the time of hospital admission. Severity of intoxication was assessed by the total dose of atropine required to relieve poisoning manifestations, the Simplified Acute Physiology Score, the need for assisted ventilation, and by a specific grading system previously validated that identified two groups of patients: group 1 (low severity, n = 18) and group 2 (high severity, n = 12).

RESULTS

Serum cholinesterase level did not correlate with the total dose of atropine or with the Simplified Acute Physiology Score. Mean serum cholinesterase level was not significantly different between group 1 and group 2 patients (448 +/- 409 U/L in group 1 compared with 611 +/- 575 U/L in group 2 (p = NS); it was also not significantly different between patients with and without mechanical ventilation support (567 +/- 571 vs 470 +/- 409, respectively).

CONCLUSION

Serum cholinesterase levels have no prognostic value in acute organophosphate poisoning. Thus, a grading system to identify high-risk patients based on this measurement is most likely unreliable.

Organophosphate poisoning: peripheral vascular resistance--a measure of adequate atropinization

We report severe organophosphate poisoning complicated by hypotension and ischemic sequelae in two patients with pre-existing vascular disease. Both patients had a low total peripheral resistance and high cardiac output that were significantly reversed by doses of atropine in excess of those required to control other muscarinic symptoms. Cerebral infarcts and gangrene requiring a below knee amputation were complications of the poisonings. It is proposed that the ischemic complications are due to paradoxical vasoconstriction by acetylcholine at sites of endothelial injury. One patient, who had taken fenthion, also had a significantly delayed peak and prolonged, 2-3 week, systemic toxicity. We propose that stability of the plasma cholinesterase at 6 to 8 h after temporarily suspending oxime provides a rapid guide to the duration of therapy, especially in patients whose complications make clinical assessment difficult.

Transport management of the patient with acute poisoning

Poisoning in children is a common clinical problem encountered by pediatricians, general practitioners, and emergency room physicians. Poisoning in children less than 5 years of age is usually accidental, whereas, in young adults, any disparity between expected history and clinical findings should suggest poisoning. It is imperative that the treating physician expeditiously recognize, begin treating, and plan to transfer, when indicated, by specialized pediatric transport team the critically ill poisoned child to a tertiary care facility.

Intermediate syndrome due to prolonged parathion poisoning

A parathion-poisoned patient with prolonged cholinesterase inhibition due to impaired hepatic metabolism and urinary excretion is reported. An intermediate syndrome characterized by respiratory paresis, weakness in the territory of several motor cranial nerves and of proximal limb and neck flexor muscles, persisted for 3 weeks. During this whole period, cholinesterase remained markedly reduced. Serial EMGs with repetitive nerve stimulation pointed to a combined pre- and postsynaptic disorder of neuromuscular transmission. Electron microscopy of an intercostal muscle biopsy showed focal degeneration at the poorly branched postsynaptic folds, and was considered to be nonspecific.

Neurological aspects of organophosphate poisoning

Besides their well-known anticholinesterase action resulting in a typical acute cholinergic crisis, organophosphorus (OP) agents are capable of producing several subacute or chronic neurological syndromes. The acute over-stimulation at the neuromuscular junction results in muscle fiber necrosis. The significance of this OP-induced myopathy in human intoxication is unknown. Organophosphate-induced delayed neuropathy (OPIDN) arises 1-3 weeks after exposure to some OP compounds all capable of remarkably inhibiting a distinct esterase called neuropathy target esterase (NTE) during a critical time period. An experimental hen model has been designed to screen new OP compounds as to their delayed neurotoxic effects. The recently described intermediate syndrome emerges 1-4 days after an apparently well-treated cholinergic crisis. It main clinical features are sudden respiratory paralysis, cranial motor nerve palsies, and proximal limb muscle and neck flexor weakness. Whether or not this is a separate entity in OP agent toxicology remains to be seen. Further studies are required to further determine its clinical and paraclinical characteristics and the actual type of underlying neuromuscular dysfunction involved.

Prolonged toxicity with intermediate syndrome after combined parathion and methyl parathion poisoning

A prolonged type of organophosphate toxicity, previously characterized as the Intermediate Syndrome, has been recognized in 6 out of 7 prospectively studied patients poisoned by insecticide containing parathion and methyl parathion in equal proportions. The clinical characteristics included respiratory paresis, weakness in the territories of several motor cranial nerves, neck flexors and proximal limb muscles, and depressed tendon reflexes, all lasting for several days or weeks. Electromyography in the early stages disclosed diverse types of impaired neuromuscular transmission. EMG normalization preceded clinical recovery. Severe plasma butyrylcholinesterase and erythrocyte acetylcholinesterase inhibition persisted along with the occurrence of Intermediate Syndrome-related symptoms. We conclude that combined parathion and methyl parathion poisoning is more likely to induce Intermediate Syndrome than parathion poisoning alone. The mechanisms underlying this difference remain obscure. The Intermediate Syndrome shows clinical and electromyographic hallmarks of combined postsynaptic impairment of neuromuscular transmission.

The intermediate syndrome in organophosphate poisoning: presentation of a case and review of the literature

A dimethoate-poisoned woman gradually developed a moderately severe cholinergic crisis that was readily treated by atropine. After being symptom-free for nearly two days, she suffered from sudden life-threatening respiratory paresis and weakness of the facial, extraocular, neck flexor and proximal limb muscles. Muscarinic symptoms were absent. Cholinesterase inhibition was severe, and EMG revealed marked decrements at low rates of repetitive nerve stimulation, and increments at a high rate. The clinical course was compatible with the Intermediate Syndrome. This syndrome seems due to persistent cholinesterase inhibition presumably leading to combined pre- and postsynaptic impairment of neuromuscular transmission. Inadequate pralidoxime therapy is proposed but not established as contributory. Prolonged monitoring of respiratory function in patients poisoned by particular organophosphate agents is mandatory.

Acute poisoning with methidathion: a case

An acute poisoning in a 50-year-old man who ingested approximately 6.2 g of the phosphorus ester methidathion is described. The patient was treated with three haemoperfusions 23, 44 and 115 h after ingestion, with continuous gastric lavage, atropine and pralidoxime administration and with prolonged mechanical ventilation. Haemoperfusion was an ineffective epuration technique since it removed only 0.22% of the ingested methidathion. The clinical course wavered because of a probable redistribution of phosphorus ester from fat to blood. A plasma level higher than 100 micrograms l-1 was associated with the most serious phases. Methidathion was present in the plasma until the sixth day, in the urine until the seventh and in the gastric juice until the eighth. Its absence in the fat biopsy made on the tenth day was an aid to therapy. The phosphorus ester did not inhibit lymphocyte neuropathy target esterase (NTE), neither did it induce development of delayed polyneuropathy.

The neurotoxicity of subchronic acetylcholinesterase (AChE) inhibition in rat hippocampus

The neurotoxic effects of long-term, low-level exposure to the commercially available insecticide, Fenthion, were examined in the present study. Young (2 month) adult, male Long-Evans rats were dermally exposed to Fenthion (25 mg/kg, 3X week) and sampled after 2 and 10 months exposure to assess neurotoxic damage in the hippocampus using morphological and biochemical endpoints. Histopathology, consisting of gliosis, swollen and necrotic neurons, and cell dropout, occurred in the dentate gyrus (DG), CA4 (hilus), and CA3 sectors as early as 2 months postexposure. Acetylcholinesterase (AChE) staining of brain tissues taken at this time was severely reduced in the septal nuclei, the DG molecular layer, the CA4, and the hippocampus proper. After 10 months exposure to Fenthion, cellular necrosis and gliosis intensified in the CA4 and CA3 regions and occasionally involved the CA2. Radiometric assays of AChE activity in the hippocampus indicated a 65 and 85% depression after 2 and 10 months exposure, respectively. Quinuclidinyl benzilate binding for the hippocampal muscarinic receptor was reduced by 6 and 15%, after 2 and 10 months exposure, respectively. A separate group of older (12 month) rats was exposed to the same dosing regimen of Fenthion and examined for neuropathological damage after 2 and 10 months exposure. Aged animals exposed for only 2 months expressed severe hippocampal degeneration in a pattern similar to that seen in the young adult after 10 months exposure (viz., DG, CA4, CA3). Aged animals exposed for 10 months showed more extensive histopathology of the CA4-2 and occasionally CA1. These observations indicate that in both young adult and aged animals, subchronic, low-level exposure to anticholinesterase compounds can result in serious neurotoxic consequences to the mammalian hippocampus.

Organophosphate poisoning

Organophosphate insecticides have become increasingly popular for agricultural, industrial, and home use and represent a significant potential health risk. We have reviewed the history, pathophysiology, clinical presentation, laboratory findings, differential diagnosis, therapy, and complications of toxic exposure to organophosphates. Promp recognition and aggressive treatment of acute intoxication are essential in order to minimize the morbidity and mortality from these potentially lethal compounds.

A severe organophosphate poisoning requiring the use of an atropine drip

A 68-year-old male attempted suicide by drinking three ounces of concentrated Cygon 2-E (23.4% dimethoate). He was immediately brought to the hospital, responded to standard treatment (ipecac, activated charcoal, 2-PAM, atropine), and was transferred from the ICU to general care 24 hours after the exposure. Within eight hours of the transfer, he relapsed and was moved to the CCU, where he required five milligrams of atropine every ten minutes for 24 hours, before being started on an atropine drip. The patient was maintained on the atropine drip (0.5-2.4 mg/kg/hr) for five weeks. He required a total atropine dose of 30 grams, the largest amount ever reported to have been administered to a human. Although S-ChE activities gradually increased they were not found to be helpful in determining when the drip could be safely stopped. Control of hypersecretions served as the best monitoring parameter for titration of the drip rate. The patient recovered completely with the exception of a detectable sensorineural hearing deficit, a slight, nonspecific personality change, and minimal spastic rigidity thought to be secondary to several anoxic episodes.