Organophosphate poisoning

Substance

Organophosphate

Commonly used as insecticides

Common name or Trade name

磷酸酯或有機磷

Involving system

-Mechanism: They bind to acetylcholinesterase (AChE), also known as red blood cell (RBC) acetylcholinesterase, and render this enzyme non-functional [1]

-Aging: After some period of time, the acetylcholinesterase-organophosphorus compound undergoes a conformational change, known as "aging," which renders the enzyme irreversibly resistant to reactivation by an antidotal oxime [2]
- possible poisoning: decreased > 50% plasma cholinesterase or RBC cholinesterase 
- severe poisoning:  decreased > 90% plasma cholinesterase or RBC cholinesterase 

Presentation

SLUDGE/BBB – Salivation, Lacrimation, Urination, Defecation, Gastric Emesis, 

                            Bronchorrhea, Bronchospasm, Bradycardia

DUMBELS – Defecation, Urination, Miosis, Bronchorrhea/Bronchospasm/Bradycardia, 

                      Emesis, Lacrimation, Salivation [3] 

 
Antidote and Treatment

- GI decontamination: poisoning less than 1 hour

- activated charcoal 1gm/Kg BW.

- Atropine: 1 to 3 mg IV for adults and 0.05 mg/kg IV for children

If no effect is noted, the dose should be doubled every three to five minutes until pulmonary muscarinic signs and symptoms are alleviated [4]

- Pralidoxime: 30 mg/kg in adults, and 25 to 50 mg/kg for children, Pralidoxime should NOT be administered without concurrent atropine in order to prevent worsening symptoms due to transient oxime-induced acetylcholinesterase inhibition [5]

Disposition

Endotracheal intubation if the respiratory failure or markedly depressed mental status

Admission to the intensive care unit if hemodynamic  changes / AMS / respiratory failure.

References

[1] Khurana D, Prabhakar S. Organophosphorus intoxication. Arch Neurol 2000; 57:600.

[2] Eddleston M, Szinicz L, Eyer P, Buckley N. Oximes in acute organophosphorus pesticide poisoning: a systematic review of clinical trials. QJM 2002; 95:275.

[3] Sidell FR. Clinical effects of organophosphorus cholinesterase inhibitors. J Appl Toxicol 1994; 14:111.

[4] Konickx LA, Bingham K, Eddleston M. Is oxygen required before atropine administration in organophosphorus or carbamate pesticide poisoning? - A cohort study. Clin Toxicol (Phila) 2014; 52:531.

[5] Johnson MK, Jacobsen D, Meredith TJ, et al. Evaluation of antidotes for poisoning by organophosphorus pesticides. Emerg Med 2000; 12:22.

--20^th, March 2020 Sheng-Teck Tan, Yu-Jang Su