Effects of Carbamates on Whole Blood Cholinesterase Activity: Chemical Protection Against Soman

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Abstract
Toxicity (LD50) of several carbamates, all reversible inhibitors of cholinesterase (ChE), were determined in male rabbits. These include isopropyl methylphenyl carbamate (IMPC), pyridostigmine, neostigmine, benzpyrinium and physostigmine. When 1/9 of LD50 of these carbamates was individually combined with atropine (A) and benactyzine (B), mecamylamide (M) or chloropromazine (CPZ) and administered to rabbits in a pretreatment regimen, most animals could be protected from a 10 LD50 challenge of Soman. If CPZ, M or B was omitted from this regimen, no rabbits survived challenge of Soman. Protection afforded against Soman was related to reversible inhibition of ChE by carbamates; reversible ChE inhibition varied with route of injection and with physical properties of carbamate. Oral administration of pyridostigmine, a quaternary carbamate, provided protection for 24 h. When pretreatment included 4 components (pyridostigmine, A, M and B), LD50 of Soman was raised 30.8 times in rabbits.