Quantitative studies of the effect of antagonists on the acute toxicity of organophosphates in rats

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Abstract
1 . The subcutaneous acute toxicities of the vinyl phosphate pesticides mono-crotophos, dicrotophos, chlorfenvinphos, crotoxyphos, dichlorvos, mevinphos, and of the experimental compounds SD 4455 (cis-2-carboxy-1-methylvinyl dimethylphosphate) and SD 7779 (cis-2-(1-phenylethoxy) carbonyl-1-methylvinyl diethylphosphate) have been determined in female rats. 2 . The effects on the log dose-probit mortality curves to the vinylphosphates of the therapeutic subcutaneous administration of methylatropine, atropine, N-methylpyridinium-2-aldoxime methanesulphonate and obidoxime have been studied. 3 . Elevation of the LD50 values by the therapeutic regimens was shown to be an unsatisfactory measure of therapeutic efficiency, while reduction of the effect of a maximally lethal dose (LD90) to less than that of a minimally lethal dose (LD10) provided a better quantitative measure of therapeutic efficiency. 4 . The combination of atropine sulphate (50 μmol base/kg) with obidoxime (250 μmol/kg) was found to be generally the most effective of the antidotal regimens. The authors thank Mr. G. R. Ellender for his valuable technical assistance and Mr. D. L. Holmes, of the Statistics Unit of the Woodstock Agricultural Research Centre, for the statistical evaluations incorporated in this work.