Pharmacokinetic profile and tissue distribution of monensin in broiler chickens

1. The pharmacokinetics of monensin, including half-life, apparent volume of distribution, total body clearance, systemic bioavailability and tissue residues were determined in broiler chickens. The drug was given by intracrop and intravenous routes in a single dose of 40 mg/kg body weight. 2. Following intravenous injection the kinetic disposition of monensin followed a two compartments open model with absorption half life of 0.59 h, volume of distribution of 4.11 l/kg and total body clearance of 28.36 ml/kg/min. The highest serum concentrations of monensin were reached 0.5 h after intracrop dosage with an absorption half-life of 0.27 h and an elimination half life of 2.11 h. The systemic bioavailability was 65.1% after intracrop administration. Serum protein-binding tendency of monensin calculated in vitro was 22.8%. 3. Monensin concentrations in the serum and tissues of chickens after a single intracrop dose of pure monensin (40 mg/kg body weight) were higher than those after feeding a supplemented monensin premix (120 mg/kg) for 2 weeks. Monensin residues were detected in tested body tissues, collected 2, 4, 6 and 8 h after oral administration. The highest concentration was found in the liver. In addition, monensin residues were detected only in liver, kidney and fat 24 h after the last oral dose. No monensin residues could be detected in tissues after 48 h, except in liver which cleared completely by 72 h.