Pharmacokinetics, tissue residue depletion and withdrawal period estimation for tylosin in geese (Anser anser domesticus) following intravenous, intramuscular, and oral administration

Tylosin, a macrolide antibiotic, is used in poultry to treat Mycoplasma-associated respiratory disease and Clostridium perfringens-associated necrotic enteritis. No pharmacokinetic or tissue residue data exist for geese, preventing the establishment of a species-specific withdrawal period.This study characterized plasma pharmacokinetics in sixteen healthy adult male Bilgorajska geese (Anser anser domesticus) using a four-period crossover design following intravenous (5 mg/kg), intramuscular (25 mg/kg), single-dose oral (100 mg/kg), and multiple-dose oral (100 mg/kg q24h × 3 days) administration. Tylosin concentrations were quantified via validated UHPLC–MS/MS and analyzed using non-compartmental methods. Tissue residue depletion in muscle, fat, liver, and kidney was assessed in a separate group of sixteen geese at 10, 24, 48, and 72 hours post-final oral dose, with withdrawal periods estimated using EMA WT 1.4 (MRL = 100 µg/kg).Systemic clearance was 0.81 ± 0.11 L/h/kg, volume of distribution 2.36 ± 0.12 L/kg, and terminal half-life approximately 2 hours across parenteral routes. Absolute bioavailability was 56 ± 19% after IM and 16–17% after oral dosing. No accumulation occurred after three days of oral administration. Liver residues were highest and most persistent; muscle and fat were below MRL by 24 hours, while kidney marginally exceeded MRL at 72 hours. Estimated withdrawal times were 2.91, 4.23, and 7.66 days for muscle, kidney, and liver, respectively, yielding a provisional withdrawal period of 8 days. These exploratory findings provide the first species-specific pharmacokinetic and residue data for tylosin in geese, identifying liver as the marker tissue and demonstrating route-dependent bioavailability differences.