ORGANOPHOSPHORUS POISONINGINTRODUCTION:Organophosphates are one of the most common causes of poisoning worldwide, and are frequently intentionally used in suicides. Organophosphorus compounds or organophosphates are commonly used in the industrial, agricultural and home settings. Some organophosphorus compounds are used as pesticides in agriculture. These are highly toxic and include tetraethyl pyrophosphate and parathione. Other organophosphates such as coumaphos, chlorpyrifos and trichlorfon are used as animal insecticides and have intermediate toxicity. Low toxicity compounds are malathione, diazinon and dichlorovos. These are used as household insecticides. Nerve gases (e.g. Sarin, Soman, Tabun and VX) are used as chemical warfare and in terrorist attacks, which disrupt the mechanism by which nerves transfer messages to organs.

CAUSES: Organophosphorus exposure occurs through inhalation, ingestion and dermal contact. Organophosphorus poisoning may be intentional or unintentional. Organophosphorus compounds are easily accessible and are often used to commit suicides. Accidental poisoning may also occur especially when they are kept within the reach of children. Farmers could get exposed while spraying crops if they are not well protected with masks, gloves and other protective clothing.

PATHOPHYSIOLOGY:

Organophosphorus compounds are powerful inhibitors of carboxylic esterase enzymes including acetylcholine esterase and pseudocholine esterase

They bind firmly to esterase enzyme, inactivating it by phosphorylation at myoneural junctions and synapses of ganglion

Acetylcholine (Ach) accumulates at parasympathetic, sympathetic and somatic sites and transfer of nerve impulses across synapses and nerve muscle junction is prevented.

Produces hyper excitation of voluntary and involuntary muscles (i.e. both sympathetic and parasympathetic)

Mild poisoning: Cholinesterase activity is 20-50% of normal. Moderate poisoning: Cholinesterase activity is 10-20% of normal. Severe poisoning: Cholinesterase activity is 80 beats/min, pupils no longer pinpoint, dry axillae and systolic blood pressure > 90mmHg. Once atropinised set up an infusion of atropine at an hourly dose of 10-20% of the total dose of atropine given initially. Review every 15 mins to see whether the atropine infusion rate is adequate. 4) Cholinesterase reactivators- Pralidoxime (2-PAM) is effective for nicotinic as well as muscarinic features of toxicity. Dose: 1-2 gm IV for adult25-50 mg/kg for childrenRepeated at 6-12 hrs interval for 24-48 hours.

5) Other measures: Diuretics and saline purgative. Barbiturate or diazepam for convulsion Symptomatic treatment Hemodialysis

References: Mathew K., Aggarwal P., Medicine Prep Manual for Undergraduates (2013), 4th edition, Published by Elsevier, A division of Reed Elsevier India Private Limited, Pg. no. 647-649 http://en.wikipedia.org/wiki/Organophosphate_poisoning http://emedicine.medscape.com/article/167726-overview#a0101 http://en.wikipedia.org/wiki/Nerve_agent