Methidathion

Methidathion is an organophosphate insecticide that inhibits insect cholinesterase.¹ It reduces cattle lice (L. vituli, D. bovis, and H. eurysternus) infestation by 99.1% when administered topically at a dose of 3.5 mg/kg.² Methidathion is selectively toxic to lice over cattle, only inhibiting cattle plasma acetylcholinesterase activity by 20% with no effect on survival when administered topically at a dose of 24 mg/kg. It increases sister chromatid exchange (SCE) in a concentration-dependent manner and induces cell cycle arrest at the M₁ phase in V79 cells when used at a concentration of 40 μg/ml.³ Dietary administration of methidathion (1.4-4.7 mg/kg) increases alanine aminotransferase, aspartate aminotransferase, sorbitol dehydrogenase, and alkaline phosphatase activity, inhibits cholinesterase, and induces chronic liver inflammation in male beagle dogs.⁴ It also induces loss of striation and myocytolysis of cardiomyocytes and reduces serum cholinesterase activity in rats when administered orally at a dose of 5 mg/kg.⁵

1.SÁnchez-Bayo, F.Insecticides mode of action in relation to their toxicity to non-target organismsJ. Environ. Anal. Toxicol.S4:002(2012) 2.Hart, R.J., Cavey, W.A., Moore, B., et al.Efficiency and safety of methidathion applied as a pour-on systemic insecticide for control of cattle liceAust. Vet. J.55(12)575-579(1979) 3.Chen, H.H., Hsueh, J.L., Sirianni, S.R., et al.Induction of sister-chromatid exchanges and cell cycle delay in cultured mammalian cells treated with eight organophosphorus pesticidesMutat. Res.88(3)307-316(1981) 4.Chang, J.C., Walberg, J.A., and Campbell, W.R.One-year dietary toxicity study with methidathion in beagle dogsFundam. Appl. Toxicol.19(2)307-314(1992) 5.Yavuz, T., Altuntas, I., Delibas, N., et al.Cardiotoxicity in rats induced by methidathion and ameliorating effect of vitamins E and CHum. Exp. Toxicol.23(7)323-329(2004)