A Mixed Effect Emax Model Applied for Determination of Malathion Optimal Dose

Background: Malathion is an organophosphate insecticide and is the most appropriate one used widely in the world. Organophosphate insecticides cause a specific biochemical defect in the body. A major cause of this wastage is inhibition of cholinesterase (ChE) enzyme. Objectives: This study was conducted to determine the optimal dose of the pesticide malathion which inhibited 50% of ChE enzyme. Materials and Methods: An experimental study was conducted on 18 male rats weighing 180-250 g. The rats were randomly divided into 6 groups. The Ellman method was used to measure the acetylcholinesterase (AChE) enzymatic activity. Doses 0, 25, 50, 100, 200 and 400 mg/kg of pesticide malathion was tested on rats to determine the dose of the pesticide malathion with 50% inhibition of the ChE enzyme, at 24, 48, and 72 hours. According to these data, Emax model was fitted, then the median effective doses of the pesticide malathion were estimated at different time intervals, separately. Results: Based on the reduction Emax model, the optimal dose 29.14 mg/kg was determined at 72 time point. Conclusion: Using the mixed effect Emax model instead of the multiple comparison methods, such analysis of variance was suggested to determine the optimal dose of organophosphates such as malathion, which provide more accurate results.