Kinetic analysis of the fate of methyl parathion in the dog

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Abstract
Methyl parathion (1, 3, 10 and 30 mg · kg−1) was injected intravenously in dogs and the serum concentrations were followed in function of time. For each dose the serum level data were fitted to a two- or tri-exponential equation by means of a non-linear least-squares regression analysis computer program. During the first hours after injection a rapid and important decrease of the serum levels was observed, whereas afterwards the levels decreased more slowly with a harmonic mean terminal half-life of 7.2 h (range 6.6–8.8 h) for the 10 mg · kg−1 dose. Simulations using the kinetic parameters obtained for the dose of 10 mg · kg−1 show that elimination of methyl parathion from the body is fast (5 h after injection only 30% of the dose is still present in the body) and that the fraction remaining is mainly located in the peripheral compartments.