Organophosphorus Poisoning

Abstract

Acute poisoning by organophosphorus (OP) compounds is a major global clinical problem, with
thousands of deaths occurring every year. Most of these pesticide poisoning and subsequent
deaths 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 toxicity
of these OP pesticides is due to the irreversible inhibition of acetylcholinesterase (AChE) enzyme
leading to accumulation of acetylcholine and subsequent over-activation of cholinergic receptors
in various parts of the body. Acutely, these patients present with cholinergic crisis; intermediate
syndrome and delayed polyneuropathy are other sequel of this form of poisoning. The diagnosis
depends on the history of exposure to these pesticides, characteristic manifestations of toxicity
and improvements of the signs and symptoms after administration of atropine. The supportive
treatment of OP poisoning includes the same basic principles of management of any acutely
poisoned patient i.e., rapid initial management of airways, breathing, and circulation. Gastric
lavage and activated charcoal are routinely used decontamination procedures, but their value
has not been conclusively proven in this poisoning. Atropine is the mainstay of therapy, and
can reverse the life threatening features of this acute poisoning. However, there are no clear
cut guidelines on the dose and duration of atropine therapy in OP poisoning. Cholinesterase
reactivators, 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 that
there are many unanswered questions and controversies in the management of OP poisoning
and there is an urgent need for research on this aspect of this common and deadly poisoning.

Key Words: poisoning, organophosphorus insecticides, decontamination, antidotes