Differential effects of aquatic anaesthetics on the pharmacokinetics of antibiotics: Examples using florfenicol in Nile tilapia (Oreochromis niloticus)

Anaesthetics are commonly applied in pharmacokinetic (PK) studies to assure smooth handling of experimental procedures or to promote animal welfare. However, the influence of anaesthetics on the PK of co‐administered drug is generally unknown but assumes ignorable. The goal of the study was to investigate the effect of tricaine methanesulfonate (MS‐222), 2‐phenoxyethanol (2‐PE) and eugenol (EUG) on the PK of florfenicol (FF) in Nile tilapia. Twenty‐eight fish were repeatedly exposed to 90 ppm EUG, 300 ppm MS‐222 or 900 ppm 2‐PE before FF oral administration (15 mg/kg) and each successive blood sampling. The serum concentration–time profiles were analysed by a 2‐compartmental model, and the generated parameters in the control (without anaesthetic) and anaesthetic groups were statistically compared. The results demonstrated that the serum concentrations of each anaesthetic were similar at every FF sampling times (70 μg/ml for MS‐222; 277 μg/ml for 2‐PE; and 61 μg/ml for EUG). In comparison with the control group, the repeated use of MS‐222 did not result in a statistical difference in most of the PK parameters. In contrast, the elimination half‐lives of the 2‐PE and EUG groups were significantly longer whereas the absorption and distribution half‐lives of the 2‐PE group were significantly shorter than the control, resulting in altered optimal dosages in the simulation modelling. Whether or not the numbers and extent of PK parameters change mitigate subsequent estimations of other PK‐derived secondary values such as dosing regimen and withdrawal time remains to be elucidated, but the auxiliary use of anaesthetics in PK studies should not assume uninfluential.