Pharmacokinetics and Tissue Distribution of Rifampicin in Carassius auratus gibelio Following Intraperitoneal Administration: An Integrated UPLC-MS/MS and Molecular Docking Study

Rifampicin is a commonly used broad-spectrum antibiotic in aquaculture, but its pharmacokinetics in fish remain poorly understood, making it difficult to accurately assess the risk of its residues. The research examined how rifampicin is distributed across tissues and its elimination kinetics in Carassius auratus gibelio after a single intraperitoneal injection at a dose of 1.5 mg/kg. A precise and dependable ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) technique was created and confirmed for measuring rifampicin in eight different tissues (muscle, liver, kidney, intestine, bile, pancreas, spleen, and brain) over a period of 456 h. Pharmacokinetic parameters were determined using a non-compartmental approach, and molecular docking was utilized to examine interactions with crucial ADME proteins such as PEPT1, CYP3A65, and P-gp. Rifampicin quickly spread to the enterohepatic system, showing the greatest concentration in the intestine (Maximum plasma concentration, Cmax 1525.85 ng/mL, Area under the concentration–time curve, AUC0-t 185,614.68 ng·h/mL) and bile, then in the liver and pancreas. The elimination half-lives differed significantly across tissues, with the brain having the longest at 90.75 h and the spleen at 88.88 h, while the kidney had the shortest at 46.70 h. The muscle showed a low peak concentration of 150.24 ng/mL but had a prolonged retention time with a half-life of 68.28 h and a mean residence time of 113.50 h, suggesting a residue profile characterized by low concentration and long retention. Enterohepatic recirculation was suggested by the multiphasic elimination curves observed in bile and intestine. The strong binding affinities of rifampicin to PEPT1 (–7.736 kcal/mol), CYP3A65 (–7.575 kcal/mol), and P-gp (–7.013 kcal/mol) were revealed through molecular docking, providing insight into the tissue-specific uptake, metabolism, and efflux. These results show that rifampicin remains in muscle tissue for long durations even with minimal accumulation, emphasizing the importance of careful residue monitoring. The combined pharmacokinetic and molecular docking method provides a useful framework for comprehending how xenobiotics are processed in fish, aiding in the scientific regulation of rifampicin in aquaculture.