Pharmacokinetics, Optimal Dosages, and Withdrawal Time of Florfenicol in Cobia ( Rachycentron canadum ) After Oral Administration via Medicated Feed

ABSTRACT Antimicrobial drugs are commonly used for the treatment of bacterial diseases in cobia ( Rachycentron canadum ), but information regarding the rationale of their therapeutic use, such as pharmacokinetics (PK), optimal dosages, and withdrawal time (WDT) in this species is very rare. The present study evaluated the PK characteristics of florfenicol (FF) in cobia at 25°C after a single oral administration of 10 mg/kg via medicated feed. FF in the serum was determined by an HPLC method and the PK parameters were analyzed by a one‐compartmental model. In tissue depletion and drug WDT study, cobia were fed with FF medicated feed at 10 mg/kg once daily for 5 days. The WDT was determined by linear regression analysis using the sum of FF and its metabolite florfenicol amine as the marker residue. The results revealed that FF has desirable PK characteristics in cobia, including a high peak serum concentration ( C max , 9.08 μg/mL), a large area under the serum concentration‐time curve (AUC, 182.68 h·μg/mL), and a moderately long elimination half‐life ( t 1/2K , 10.22 h). The optimal dosage for a minimum inhibitory concentration (MIC) of 2 μg/mL at 25°C was 6.23 mg/kg/day. The WDT was calculated to be 5 days based on muscle/skin and 6 days based on serum depletion. Since serum sampling can reduce animal use, it warrants further investigation despite not being an official target tissue for WDT. Our findings indicated that FF is a good choice for treating bacterial diseases in cobia due to its favorable PK profile and short WDT.