Protection against lethal organophosphate poisoning by quaternary pyridine aldoximes.

The effect of 18 pyridinium aldoximes on diethylphosphoryl-acetocholinesterase in vitro and the protection against lethal poisoning by ethyl pyrophosphate (TEPP) in mice pretreated with 0.095 m.mole/kg. of these oximes was investigated. Monoximes and dioximes of polymethylenebispyridinium compounds were studied in greater detail since they were up to 22 times more potent than pyridine-2-aldoxime methiodide (2-hydroxyiminomethyl-N-methylpyridinium iodide) in reactivating diethylphosphoryl-acetocholinesterase in vitro and protected mice against lethal poisoning by up to 15 LD100 of ethyl pyrophosphate. These oximes were also up to 52 times more potent than pyridine-2-aldoxime methiodide in reactivating di-isopropylphosphoryl-acetocholinesterase in vitro and were effective in preventing lethal poisoning by dyflos (di-isopropyl phosphorofluoridate). The antidotal action against diethyl phosphostigmine (Ro 3-0340) was even greater than that against ethyl pyrophosphate. Some of the most effective oximes had antidotal actions in poisoning by ethyl pyrophosphate, diethyl phosphostigmine and dyflos when given in 0.0095 m.mole/kg. and this effect was enhanced by 1 mg./kg. atropine sulphate. In vivo reactivation of diethylphosphoryl-acetocholinesterases by 0.0095 or 0.095 m.mole/kg. of oximes of polymethylenebispyridinium compounds was demonstrated in blood but not in brain. Atropine-like and neuromuscular blocking activities were studied on isolated organs and protection against lethal doses of neostigmine and related anticholinesterases were also investigated. Some of the oximes of polymethylenebispyridinium compounds have, relative to pyridine-2-aldoxime methiodide, a higher therapeutic ratio in mice and considerably greater water-solubility. The possible advantages to be gained from their use in preference to pyridine-2-aldoxime methiodide are discussed.