VPT 421: Veterinary Toxicology (2+0)

ORGANOPHOSPHORUS COMPOUNDS - INTRODUCTION

• Organophosphorous compounds are used as insecticides and parasiticides. They include malathion, parathion, tetraethyl pyrophosphate, dimethoate, coumaphos, fenchlorphos, trichlorphon etc.
• They are either aliphatic carbon, cyclic and heterocyclic phosphate esters. In organothiophosphates, the double-bonded oxygen is replaced with a sulphur molecule.
• Esters with a P = S functional group are usually less toxic than those with a P = O group.
• Conversion of P = S to P = O functional group increases the anticholinesterase activity of the insecticide.
• Organothiophosphates are usually more resistant to non-enzymatic hydrolysis which might occur in the environment.
• Tetraethyl pyro phosphate (TEPP) was the first organophosphate introduced during the World war II.
• Extremely toxic nerve gases tabun and serin were introduced later.
• They were highly toxic to mammals.
• On the basis of their activity, organophosphates are classified as directly acting and indirectly acting.
• The metabolite is responsible for the toxicological actions in indirectly acting organophosphorus compounds.
• Directly acting include TEPP, DFP, tabun, serin, soman and diazinon.
• Indirectly acting includes malathion, parathion, fenithion and fenitrothion.