LAUSR

Abstract The present study was designed to explore the pharmacokinetics and tissue levels of oxytetracycline in the Pacific white shrimp (Penaeus vannamei) after oral administration of a single-dose (100 mg/kg) and multiple doses (100 mg/kg, six times). Oxytetracycline concentrations in the hemolymph, hepatopancreas, and muscle of Pacific white shrimp were determined using high-performance liquid chromatography. Pharmacokinetic parameters were analyzed based on the statistical moment theory. The results showed faster absorption of oxytetracycline in hepatopancreas (Tmax = 1 h) than in the hemolymph (Tmax = 6 h) and muscles (Tmax = 6 h) after single-dose oral administration. Meanwhile, the oxytetracycline peak concentration in the hepatopancreas was the highest (> 140 μg/g), followed by the concentration in the hemolymph (> 25 μg/mL), with the lowest concentration in the muscle ( hemolymph > muscle, indicating that the hepatopancreas is the main organ involved in oxytetracycline metabolism in Pacific white shrimp. The t1/2z value of oxytetracycline in the hemolymph, hepatopancreas, and muscle were 11.01 h, 14.90 h and 23.53 h, respectively, indicating that oxytetracycline elimination in the muscle was the slowest among the tissues. In multiple-dose oral administration, some accumulation of oxytetracycline occurred in the hemolymph and muscle, while in the hepatopancreas, oxytetracycline reached a steady state following multiple-dose administration. The t1/2z values of oxytetracycline in the tissues were 20.52 h, 18.89 h, and 35.39 h, respectively, indicating that oxytetracycline elimination after multiple-dose administration in different tissues was slower than that after a single dose. In addition, the AUCss, Ctrough, and Cav values of oxytetracycline were graded as hepatopancreas > hemolymph > muscle, showing that the hepatopancreas also plays an important role in drug metabolism and elimination after multiple-dose oral administration.