Pharmacokinetics and Withdrawal Period of Oxolinic Acid in Silver Pompano Following In‐Feed Administration of the Recommended Therapeutic Dose

Oxolinic acid (OA) is a widely recommended antimicrobial agent for managing Gram-negative bacterial infections in aquaculture. This study investigates the pharmacokinetics and withdrawal period of OA in Trachinotus blochii, a high-value mariculture species, under tropical conditions. A single oral dose of 12 mg/kg was administered, and OA levels were quantified using Liquid Chromatography-Tandem Mass Spectrometry across 12 time points from plasma, intestine, liver, kidney, and gills. Maximum concentrations (C_max) were reached within 6 h (T_max). C_max (μg/Kg) followed the order: plasma (99.77) < liver (666.67) < intestine (1764.67) = gill (1776.67) = kidney (1783.33). The elimination half-life (T_½) was longest in the kidney, followed by the liver and intestine, whereas plasma and gills exhibited faster elimination. Tissue/plasma ratios were 4.6 (liver), 8.4 (gill), 13.95 (kidney), and 17.12 (intestine). The results demonstrated that OA was rapidly absorbed from the intestine, distributed extensively, and eliminated quickly through renal, intestinal, and branchial routes. The kidney played a key role in OA elimination. In the withdrawal study, after 7 days of in-feed administration at the therapeutic dose, OA exceeded the recommended maximum residue limit in edible tissues at 6 h. The drug levels dropped below detectable limits within 24 h. Applying a 30% safety margin, a withdrawal period of 31.2 h (or 37.7°C- days) is recommended. The findings provide a practical framework for the responsible and effective use of OA in T. blochii mariculture, promoting aquaculture sustainability and food safety.