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 (<30 ng mL −1 ). On the other hand, the average drug residue concentration in muscles was 930 and 1070 ng mL −1 on day 1 and day 3, respectively, and in the liver, it was 35 and 95 ng mL −1 on day 1 and day 3, respectively, after 80 mg kg −1 BW AMX administration. However, the residue concentrations in the muscle and liver on day 5 after 80 mg kg −1 BW administration were below the detection limit (<30 ng mL −1 ). The pharmacokinetic information derived from Japanese eel can be used to design rational dosing regimens and can also assist the Taiwan government in formulating laws and regulations for AMX residues in Japanese eels. Additionally, this information will provide greater protection to consumers of aquaculture products.
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