Pharmacokinetics and tissue residue study of amoxicillin following multiple dose oral administration in broiler birds

The study was conducted to evaluate the pharmacokinetics and tissue residue levels of amoxicillin in broiler birds when administered orally at 20 mg.kg^-1 b.w.as repeated dose for five consecutive days. Plasma and tissue samples were collected and analyzed using high performance liquid chromatography (HPLC). After a multiple dose, amoxicillin showed a maximum plasma concentration (C_max) of 2.215±0.099 μg.mL^-1, a volume of distribution (V/F) of 4.107±0.231 L.kg^-1, and an elimination half-life (t_1/2²) of 3.429±0.404 hours after the first dose. However, after the final dose of the multiple-dose regimen, the maximum plasma concentration (C_max) was 1.773±0.082 μg. mL^-1, with a volume of distribution (V/F) of 4.985±0.408 L.kg^-1, and an elimination half-life (t_1/2²) of 5.247±0.908 hours was observed. Tissue residue analysis revealed the highest amoxicillin concentration in the kidney (1.616±0.248 μg.g^-1) at 24 hours, No detectable amoxicillin residues remained in the spleen, heart, lungs, muscle and fat after 72 hours of multiple-dose administration. Based on the study the withdrawal period of 3 days for single dose oral administration and 6-7 days for multiple dose oral administration is recommended.