Pharmacokinetics and plasma protein binding of oxytetracycline in ducks ( Anas platyrhynchos ) following intravenous, intramuscular, subcutaneous and oral administration

1. Tetracyclines are among the most widely used antibiotics in poultry, with oxytetracycline (OTC) playing a key role due to its routine administration via feed and water to treat susceptible bacterial infections. Despite its widespread clinical use, understanding of the pharmacokinetics of OTC in the genus Anas remains remarkably limited. The following study characterised the pharmacokinetic profile of OTC after intravenous (IV), intramuscular (IM), subcutaneous (SC) and oral administration in ducks (Anas platyrhynchos).2. A total of 24 ducks (six per group in a parallel study) were given OTC at a dose of 40 mg/kg via IV, IM, SC and oral routes. Blood samples were collected at various time points ranging from 0 min (control) to 96 h post-administration. The samples were examined by high-performance liquid chromatography (HPLC) and the pharmacokinetic parameters were assessed through non-compartmental analysis.3. Following IV administration, the volume of distribution (2.73 l/kg) suggested extensive tissue penetration. Elimination half-lives were 12.69 h (IM), 13.54 h (SC) and 12.62 h (oral), all slightly longer than after IV dosing (9.72 h) with no significant differences between extravascular routes. Bioavailability was high after parenteral administration (≈90–98%), suggesting near-complete absorption, whereas oral bioavailability was low (≈17%), indicating gastrointestinal absorption as the main limiting factor. Plasma protein binding was high (87–93%).4. Parenteral administration of OTC (40 mg/kg) in ducks can achieve effective exposure against pathogens with minimum inhibitory concentration (MIC) ≤0.5 µg/ml.