Pharmacokinetic study of amoxicillin in Japanese eel Anguilla japonica by high performance liquid chromatography with fluorescence detection

Amoxicillin (AMX) is widely used for the treatment of gastrointestinal and systemic infections. AMX residues above certain levels may pose a threat to human health. Therefore, this study aimed to understand the pharmacokinetics of AMX in Japanese eel, Anguilla japonica, using high-performance liquid chromatography (HPLC) with fluorescence detection. Japanese eels were treated with AMX at concentrations of 40 or 80 mg kg−1 body weight (BW) daily via oral administration. The results revealed that the recoveries of AMX from the muscle, liver, and sera of eels were 84.7–105.1%, 81.8–104.9%, and 88.6–106.3%, respectively. The observed peak retention time was approximately 4.2 min. After administration of 40 mg kg−1 BW per day of AMX, the pharmacokinetic parameters were detected, respectively. The average drug residue concentration in muscles was 180 and 260 ng mL−1 on day 1 and day 2, respectively, and in the liver, it was 70 and 110 ng mL−1 on day 1 and day 2, respectively, after the 40 mg kg−1 BW daily AMX administration. Residue concentrations in the muscle and liver on day 3 after 40 mg kg−1 BW administrations were below the limit of detection (