Possible antidotes in severe intoxication with fenitrothion in rats.

We investigated antidotal effects of nine drugs against acute fenitrothion poisoning in rats. The antidotal effects were evaluated by a relief from toxic signs, an increased survival ratio and a prolonged surviving time. In the poisoning with approximate LD50 fenitrothion (500 mg/kg), oximes such as 2-PAM (2-pyridine aldoxime methiodide) and TPMM (1-(methyl morphorinium)-3-(4-hydroxyiminomethylpyridinium) propane dibromide), diphenhydramine and parasympatholytics such as atropine, scopolamine and biperiden significantly increased survival ratio and/or prolonged surviving time. These effective drugs did not sufficiently depress the toxic signs, except that the parasympatholytics markedly blocked salivation, miosis and motor ataxia. In contrast, reduced glutathione and central depressants such as diazepam and phenobarbital made the poisoning serious. In the poisoning with 100% lethal dose of fenitrothion (800 mg/kg), the parasympatholytics were more effective than 2-PAM and diphenhydramine, and they elevated the survival ratio up to 20-40%. The best therapy against the severe poisoning with 100% lethal dose of fenitrothion was confirmed to be the repeated and combined treatment with atropine and 2-PAM as established in parathion poisoning, resulting in 90% survival ratio and considerable alleviation from the toxic signs.