Enrofloxacin is a broad-spectrum fluoroquinolone antibiotic widely used in aquaculture. It is primarily employed for the prevention and treatment of infectious diseases caused by common pathogenic bacteria such as Aeromonas , Edwardsiella , and Vibrio . This study investigated the pharmacokinetics, withdrawal period, and dietary risk of enrofloxacin in largemouth bass ( Micropterus salmoides ) following bath administration. Preliminary trials (5–40 mg/L) revealed dose- and time-dependent drug absorption, leading to the selection of a 40 mg/L for 6 h regimen for the main experiment. Enrofloxacin and its metabolite ciprofloxacin were quantified using a validated HPLC-FLD method, and pharmacokinetic parameters were analyzed by non-compartmental modeling. The results showed that enrofloxacin was rapidly but unevenly distributed among tissues. Peak concentrations were reached immediately in plasma, muscle with skin, and kidney, whereas peak levels in the liver were delayed by 1 h. Total tissue exposure, expressed as the area under the concentration-time curve from zero to infinity (AUC 0–∞ ), exhibited a descending order: plasma > kidney > liver > skin-on muscle. Although elimination was generally slow, tissue-specific differences were observed: the half-lives were comparable in plasma, skin-on muscle, and kidney (approximately 134–140 h), but significantly shorter in the liver (90.56 h). PK/PD analysis indicated potent efficacy against susceptible pathogens (MIC ≤ 1.1 μg/mL) and a low risk of resistance development. In contrast, dietary risk assessment suggested a potential health concern (HQ ≥ 1) within 72 h post-treatment. Accordingly, a withdrawal period of 37 days (925 ℃·days) was established for muscle with skin to ensure that total residues (enrofloxacin + ciprofloxacin) fell below the maximum residue limit (MRL). This study provides a scientific basis for the rational use, withdrawal time determination, and food safety evaluation of enrofloxacin in largemouth bass under bath administration. • 40 mg/L (6 h) dosing effective against target pathogens (MIC ≤1.1 μg/mL). • Total tissue exposure (AUC 0–∞ ) follows the order: plasma > kidney > liver > muscle with skin. • The elimination half-lives were 140.12 h in plasma and 136.07 h in muscle with skin. • A health risk (HQ ≥ 1) is predicted within 72 h post-treatment upon consuming treated fish. • A withdrawal period of 37 days (925 °C·days) is recommended.
Shan et al. (Thu,) studied this question.