Organophosphorus Poisoning

Abstract

Acute poisoning by organophosphorus (OP) compounds is a major global clinical problem, withthousands of deaths occurring every year. Most of these pesticide poisoning and subsequentdeaths occur in developing countries following a deliberate self ingestion of the poison. Metacid(Methyl parathion) and Nuvan (Dichlorovos) are commonly ingested OP pesticides; Dimethoate,Profenofos, and Chlorpyrifos are other less frequently ingested compounds in Nepal. The toxicityof these OP pesticides is due to the irreversible inhibition of acetylcholinesterase (AChE) enzymeleading to accumulation of acetylcholine and subsequent over-activation of cholinergic receptorsin various parts of the body. Acutely, these patients present with cholinergic crisis; intermediatesyndrome and delayed polyneuropathy are other sequel of this form of poisoning. The diagnosisdepends on the history of exposure to these pesticides, characteristic manifestations of toxicityand improvements of the signs and symptoms after administration of atropine. The supportivetreatment of OP poisoning includes the same basic principles of management of any acutelypoisoned patient i.e., rapid initial management of airways, breathing, and circulation. Gastriclavage and activated charcoal are routinely used decontamination procedures, but their valuehas not been conclusively proven in this poisoning. Atropine is the mainstay of therapy, andcan reverse the life threatening features of this acute poisoning. However, there are no clearcut guidelines on the dose and duration of atropine therapy in OP poisoning. Cholinesterasereactivators, by regenerating AChE, can reverse both the nicotinic and muscarinic effects;however, this benefit has not been translated well in clinical trials. All these facts highlight thatthere are many unanswered questions and controversies in the management of OP poisoningand there is an urgent need for research on this aspect of this common and deadly poisoning.Key Words: poisoning, organophosphorus insecticides, decontamination, antidotes