Pharmacokinetics of neomycin in plasma, urine, and feces of donkeys (Equus asinus) after a single intragastric administration

Neomycin is an aminoglycoside antibiotic widely used in veterinary medicine for the treatment of gastrointestinal infections. However, pharmacokinetic studies of neomycin in donkeys are limited. The present study aimed to investigate the pharmacokinetic profiles of neomycin in donkey plasma, urine, and feces following a single intragastric administration, and to evaluate its suitability for clinical use in donkeys. A total of five healthy male donkeys with similar body weights were selected and administered a single dose of 30 mg·kg^-1 body weight (BW) neomycin by gavage. The concentrations of neomycin in plasma, urine, and feces were determined. The results showed that neomycin was rapidly absorbed in donkeys, with a T_max of 0.85 ± 0.36 h and a C_max of 4.05 ± 1.99 μg·mL^-1 in plasma. The elimination half-life (T_{₁/₂<i>λ</i>} ) was 32.14 ± 12.71 h, indicating a slow elimination rate. The cumulative excretion of neomycin in urine accounted for 15.08% of the administered dose, while fecal excretion accounted for 70.99%, suggesting low systemic absorption following intragastric administration. In conclusion, the low systemic absorption and high fecal excretion of intragastric neomycin in donkeys justify its use for intestinal infections. Given the prolonged elimination half-life of the absorbed drug, its use should be restricted to local intestinal therapy to minimize systemic exposure and toxicity risks. This study contributes to the advancement of precision medicine in donkey internal medicine, offering an evidence-based foundation for optimizing therapeutic strategies and minimizing systemic risks in donkeys.