Organophosphorus Poisoning

About

Organosphosphorus compounds are used as insecticides and chemical warfare. They are easily accessible, thus they are a commonly associated with suicides and accidental poisoning.

Organophosphorus compounds or organophosphates are commonly used in the industrial, agricultural and home settings. They were initially developed as insecticides but some of them i.e. sarin, soman, tabun and VX have been developed as "nerve gases". These are used as chemical warfare and in terrorist attacks.

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.

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.

The nervous system is made up of a large number of nerves. When a signal reaches the end of a nerve, it releases a substance called neurotransmitter that carries the signal to the adjacent nerves or organ such as muscle or gland. Many nerves release acetylcholine as the neurotransmitter. Once the signal passes to the next nerve, an enzyme called choline esterase destroys the acetlycholine. Organophosphorus compounds block this enzyme, thus preventing the breakdown of acetylcholine. Thus acetlycholine acts for an excessively long time causing symptoms like twitches and increased secretions. After some time, the muscles gets fatigued leading to paralysis.

Organophosphorus poisoning is treated using drugs that block the action of acetylcholine i.e. atropine and drugs that regenerate the cholinesterase enzyme i.e. pralidoxime and obidoxime. Diazepam is used to control seizures caused due to the poisoning.

References:

1. Cherian MA, Roshini C, Peter JV, Cherian AM. Oximes in organophosphorus poisoning Indian Journal of Critical Care Medicine 2005 ; 9 (3): 155-163.
2. Goodman and Gilman. The Pharmacological Basis of Therapeutics 11^th edition.