Treatment of acute organophosphate poisoning: evidence of a direct effect on central nervous system by 2-PAM (pyridine-2-aldoxime methyl chloride)

Cation-Exchangeable Pralidoxime Chloride@bio-MOF-1 as a Treatment for Nerve Agent Poisoning and Sulfur Mustard Skin Poisoning in Animals

A 2-PAM@bio-MOF-1 composite was prepared by cationic exchange of counter N,N-dimethylammonium cations in the pores of the anionic, biocompatible metal-organic framework (bio-MOF-1) with pralidoxime chloride (2-PAM-Cl) by impregnation. In vitro drug release measurements revealed that the release rate of 2-PAM from 2-PAM@bio-MOF-1 in simulated body fluid (SBF) was more than four-fold higher than that in deionized water, indicating that the presence of endogenous cations in SBF triggered the release of 2-PAM through cation exchange. The release of 2-PAM was rapid within the first 10 h but was much slower over the period of 10-50 h. At room temperature, the maximum release rate of 2-PAM was 88.5% (15 mg of 2-PAM@bio-MOF-1 in 1 mL of SBF), indicating that the drug was efficiently released from the composite MOF in SBF. In simulated gastric fluid, 64.3% of 2-PAM was released from bio-MOF-1 into the simulated gastric fluid after 50h. This suggested that 2-PAM@bio-MOF-1 might be effective for enabling the slow release of 2-PAM in the human body. Indeed, the maximum reactivation rate of acetylcholinesterase in sarin-poisoned mice reached 82.5%. In addition, 2-PAM@bio-MOF-1 demonstrated the ability to adsorb and remove sulfur mustard (HD) in solution and from the skin of guinea pigs.

[Acute poisoning by pesticides in children]

Acute pesticide poisoning in children is rare but potentially serious. Some clinical patterns (toxidromes) are suggestive of the drug class: cholinergic crisis for organophosphate or carbamate insecticides; neurological syndrome for rodenticides; digestive and respiratory syndrome for herbicides. Treatment is symptomatic and only a few patients are treated with an antidote: atropine and pralidoxime for organophosphate insecticides, vitamin K for anticoagulant rodenticides.

Organophosphorus and carbamate insecticide poisoning

Both organophosphorus (OP) and carbamate insecticides inhibit acetylcholinesterase (AChE), which results in accumulation of acetylcholine (ACh) at autonomic and some central synapses and at autonomic postganglionic and neuromuscular junctions. As a consequence, ACh binds to, and stimulates, muscarinic and nicotinic receptors, thereby producing characteristic features. With OP insecticides (but not carbamates), "aging" may also occur by partial dealkylation of the serine group at the active site of AChE; recovery of AChE activity requires synthesis of new enzyme in the liver. Relapse after apparent resolution of cholinergic symptoms has been reported with OP insecticides and is termed the intermediate syndrome. This involves the onset of muscle paralysis affecting particularly upper-limb muscles, neck flexors, and cranial nerves some 24-96 hours after OP exposure and is often associated with the development of respiratory failure. OP-induced delayed neuropathy results from phosphorylation and subsequent aging of at least 70% of neuropathy target esterase. Cramping muscle pain in the lower limbs, distal numbness, and paresthesiae are followed by progressive weakness, depression of deep tendon reflexes in the lower limbs and, in severe cases, in the upper limbs. The therapeutic combination of oxime, atropine, and diazepam is well established experimentally in the treatment of OP pesticide poisoning. However, there has been controversy as to whether oximes improve morbidity and mortality in human poisoning. The explanation may be that the solvents in many formulations are primarily responsible for the high morbidity and mortality; oximes would not be expected to reduce toxicity in these circumstances. even if given in appropriate dose.

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.

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.

Does pralidoxime affect outcome of management in acute organophosphorus poisoning?

Acute organophosphorus (OP) poisoning is usually treated with atropine plus cholinesterase reactivators such as oximes, but controlled trials to assess the efficacy of oximes in OP poisoning have not been done. A period when the acetyl cholinesterase reactivator pralidoxime chloride was not available in Sri Lanka gave us the opportunity to compare atropine alone for treatment of moderate to severe OP poisoning (21 patients) with atropine plus pralixodime (24 patients). Outcome, as assessed clinically, was similar in the two groups. These results cast doubt on the necessity of cholinesterase reactivators for treatment of acute OP poisoning.

Treatment of acute organophosphate poisoning

The biochemistry and pharmacology of poisoning by organophosphorus esters and carbamates are outlined and methods of diagnosis and treatment are discussed. Treatment consists of reduction of exposure by decontamination, induction of vomiting or gastric lavage; pharmacological treatment with atropine and oximes (pralidoxime and obidoxime); and supportive treatment with artificial respiration and centrally acting drugs such as diazepam. The sequence of treatment depends solely on the severity of poisoning.

Antidotal therapy of severe acute organophosphate poisoning: a multihospital study

Out of 859 consecutive cases treated for exposure to organophosphate (PO) insecticides, 53 were included in the study. Criteria for inclusion were severe OP poisoning necessitating artificial ventilation, intensive care monitoring and treatment according to a standard protocol. The protocol was based on relatively high doses of obidoxime, relatively low doses of atropine and overriding with a pacemaker in cases of ventricular arrhythmias and prolonged Q-T interval. Seven patients died during hospitalization. Thirty-two patients (60%) had major central nervous system (CNS) involvement. Five (9.4%) presented severe psychiatric sequelae. Twenty-two patients (41.5%) presented cardiac arrhythmias. Five (9.4%) had liver dysfunction. High frequency of cardiac arrhythmias was observed in patients who received high cumulative doses of atropine and obidoxime; impairment of liver functions was significantly higher in patients who received high cumulative doses of obidoxime. We conclude that each drug should be titrated separately: atropine dosage should be adjusted to the severity of tracheobronchial secretions and bronchospasm, while full doses of obidoxime are justified for the period before "aging" sets in.

CNS involvement in acute organophosphate poisoning: specific pattern of toxicity, clinical correlates and antidotal treatment

The present review was designed to integrate both experimental and clinical data and to focus on the problems of management of severe cases of acute organophosphate poisoning, which always show CNS involvement. AChE activity, in discrete regions of the human brain, was studied by quantitative histochemistry of 40 mu thick sections. The regional effects of AChE inhibition by organophosphates was examined in a comparative study of the brains of two victims and two control brains, matched for age and sex. The pattern of AChE inhibition was regionally selective. The most significant decreases were observed in the neocerebellum, thalamic nuclei and the cortex. This specific distribution of AChE inhibition may be correlated with some of the clinical characteristics of acute organophosphate poisoning. The diagnostic value of blood AChE levels was examined in a personal series of 53 patients, who needed artificial ventilation, intensive care monitoring and antidotal treatment. The effects and side-effects of the antidotal treatment were reassessed. Recommended regimen of therapy was outlined, based upon experience in this series and in recent animal studies. The logical therapy would be and almost always in the co-administration of an anticholinergic drug (usually atropine) and an AChE reactivator (oximes) in order to rapidly obtain the most beneficial effect in the critically ill patient. Seizures that do not respond to the specific antidotal therapy, should be treated with I.V. benzodiazepines. Artificial respiration and supportive measures are essential for patient' survival. They enable the patient to gain the necessary time for sufficient recovery of AChE activity.