Bath immersion pharmacokinetics of florfenicol in Nile tilapia (Oreochromis niloticus)

Pharmacokinetics, withdrawal period and risk assessment of enrofloxacin in the northern snakehead (Channa argus) following bath administration

Enrofloxacin (ENR) is widely used in aquaculture practice, but little is known about its pharmacokinetic, withdrawal period and dietary risk in fish via bath administration. The purpose of this study was to provide data support for the use of ENR bath therapy in the northern snakehead (Channa argus). The pilot study was carried out to evaluate the therapy concentrations of ENR in northern snakehead with immersion concentrations ranged from 5 to 40 mg/L for 6 h. Based on results of the pilot study, an ENR immersion concentration of 20 mg/L was used for the formal experiment. At this dose, the peak concentrations of ENR in plasma, muscle plus skin, liver and kidney were 4.85, 4.55, 3.87 and 7.42 μg/mL (or g), respectively. According to the AUC0-∞ values, the distribution of ENR in northern snakehead followed the order of kidney > plasma > liver > muscle + skin. The elimination of ENR in northern snakehead was very slow, the half-lives (T1/2λz ) were up to 90.31, 85.5, 104.56 and 120.9 h in plasma, muscle plus skin, liver and kidney, respectively. Ciprofloxacin (CIP) was not detected in any samples in the pilot study and was only occasionally detected in muscle plus skin and liver samples in formal experiment. Based on the calculated PK/PD index AUC/MIC and Cmax /MIC, the current bath treatment regimen will have a good therapeutic effect on infections caused by bacteria with MIC below 0.6 μg/mL. The dietary risk assessment suggested that there was a dietary risk (Hazard Quotients > 10%) until day 6 after bath treatment. It is mandatory for ENR to maintain a withdrawal period of at least 450°C-day in northern snakehead after bath treatment ceased.

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.

Temperature-dependent pharmacokinetics of trichlorfon in common carp (Cyprinus carpio L.) after bath immersion therapy

The common carp (Cyprinus carpio L.) is one of the most important freshwater fish species. As C. carpio culture has escalated, bacterial and parasitic infections have become a real threat to the industry. Antibacterial and antiparasitic treatments are provided for infection control in C. carpio. However, adequate vaccines have not yet been developed. Trichlorfon (TCF), an organophosphate, is an antiparasitic agent used in aquaculture to treat external parasites. However, there are few pharmacokinetic (PK) studies on its use in fish. This study investigated the residue elimination and temperature-dependent PK characteristics of TCF in C. carpio at 15°C and 25°C after 30 mg/L TCF bath immersion for 30 min. TCF residue concentrations in plasma and muscle tissues were determined using liquid chromatography-tandem mass spectrometry and further analyzed using a noncompartmental model. Temperature significantly affected specific PK parameters. Increasing the temperature from 15°C to 25°C shortened the elimination half-life from 36.07 to 22.72 h. The time to reach the maximum plasma TCF residue concentration (C_max ) (T_max ) remained the same (0.5 h), but C_max increased from 67.72 to 70.76 µg/L. The area under the plasma concentration-time curve decreased from 1,057.31 to 962.14 h∙µg/L. The muscle TCF C_max was 446.99 µg/L with a corresponding T_max of 0.5 h at 25°C, and 267.53 µg/L, with a corresponding T_max of 1.0 h at 15°C. The temperature-sensitive PK parameters, such as increased in C_max and decreased elimination and distribution rates, significantly affected the plasma TCF residue concentration and its overall exposure to increasing temperature. Temperature affected the therapeutic outcomes of TCF treatment in C. carpio and likely other freshwater fish. Therefore, proper dosing regimens should take temperature into consideration.