Pharmacokinetics and Chicken Meat Residue of Tilmicosin after Administration Through Drinking Water in Broiler Chicken

Background: Tilmicosin is an antimycoplasmic drug of great utility in controlling mycoplasmosis in chicken. The drug despite its efficacy, has a high residue impact leading to a long withdrawal period. In this study, an attempt has been made to rationalize the dosage to reduce the residue burden by adopting a lower dose. Methods: The dose of tilmicosin was arrived at based on a pilot study wherein different doses were administered, and the levels were checked in plasma and meat. In the main study, tilmicosin was administered to broiler chicken as a bolus oral dose or “in drinking water” at the dose rate of 25 mg. kg-1 body weight. Blood was collected at different time points for the study. A trial to assay drug residues in tissues was also carried out. The assay of tilmicosin in chicken plasma/tissues was done using a sensitive HPLC assay. Result: In both pharmacokinetics study groups, tilmicosin concentrations could be reasonably detected only in 4 of the eight birds tested. In the birds that responded, the mean plasma concentrations remained above the MIC values of 0.05 µg.ml-1. The residue level in the lung and muscle could be detected up to day 14, and no residue from 18th day, after administration of tilmicosin through drinking water. The lung, the organ of mycoplasma infection revealed high concentrations of tilmicosin up to 14 days after the last dose. The results show that the Tilmicosin administered at a reduced rate of 25 mg.Kg-1 can be useful therapeutically, with a reduced residue burden in broiler chicken.