Pharmacokinetics and Tissue Distribution of Florfenicol in Pacific White Shrimp (<scp><i>Litopenaeus vannamei</i></scp>) Following Oral Gavage and Medicated Feed Administration

Information on pharmacokinetics (PK) and tissue residues is critical for responsible drug use. The present study aimed to investigate PK characteristics and tissue distribution of florfenicol (FF) in Pacific white shrimp following a single dose of 150 mg/kg administered via oral gavage and medicated feed. Tissue depletion study and withdrawal time determination were performed after FF-medicated feed administration at a dosage of 150 mg/kg/day for 10 days. Furthermore, the effectiveness of FF against shrimp pathogens, Vibrio spp., was tested in vitro and in vivo, using broth microdilution technique and bacterial challenge experiment (immersion with Vibrio parahaemolyticus 10⁵ CFU/mL), respectively. Following the oral gavage, the peak concentration (C_max) in hemolymph was 162.81 μg/mL (at 0.14 h), and the area under the concentration-time curve (AUC) was 71.44 h·μg/mL, whereas those of the medicated feed method were much lower, being 6.84 μg/mL (at 0.40 h) and 8.25 h·μg/mL, respectively. The elimination half-lives (t_1/2β) of the two routes were very short and comparable, being 0.77 and 0.75 h, respectively. The hemolymph protein binding was 10.42%. FF was well distributed to the muscle, producing an AUC comparable to that of the hemolymph, but it was depleted at a slower rate. Drug residue was not found in the hemolymph and muscle at 24 h after the 10-day multiple dosing. The extremely fast drug elimination renders it practically ineffective in treating vibriosis in shrimp, despite demonstrating high efficacy against Vibrio spp. in vitro. Consequently, FF may not be an ideal treatment option for Vibrio spp. infections in shrimp aquaculture.