(M1230-10-69) Population Pharmacokinetics of Enrofloxacin and Florfenicol in the Giant Danio (Devario aequipinnatus) following Oral and Bath Administration

Purpose: The zebra danio (Danio rerio) is a vital genetic model for human medical research, but bacterial infections are a significant issue in this species. Limited studies with small sample sizes have been conducted on the pharmacokinetics (PK) of antibiotics in zebrafish. This study aims to determine the PK of enrofloxacin and florfenicol using oral and bath therapy in giant danios, and compare bioavailabilities and drug exposures after both routes of administration. The results will enhance our understanding of antibiotic therapy in zebrafish and provide essential information for future research in this field.

Methods: Drug concentrations of enrofloxacin and florfenicol in blood were determined by UPLC-MS/MS (lower limit of quantification: 0.01 to 4 mg/L for blood and from 0.05 to 4 µg/g for muscle tissue samples). The oral administration of both drugs was prepared at 60 mg/kg. For the enrofloxacin bath pilot study, animals remained in the bath for 5 hours after adding at a concentration of 8 mg/L enrofloxacin. Drug concentrations of Enrofloxacin were determined at 2, 4, 10, 24, and 48 h (oral dosing) and 0.25, 1, 4, 10, 24, and 48 h (bath dosing) to assess the PK profiles. Based on our optimal sampling design analysis, the blood and muscle samples of oral florfenicol were studied at 1, 3, 6, 12, and 24 h.

Results: The bioanalytical assay could quantify florfenicol and enrofloxacin in blood and muscle samples at all sampling time points (up to 48 hours after gavage feeding). Florfenicol was absorbed relatively rapidly (half-life: 16.3 min) and had an apparent total clearance of 1.89 mL/h. Enrofloxacin was rapidly absorbed orally (half-life: 14.0 min) and its apparent total clearance (CL/F) was 1.17 mL/h. At an oral dose of 8 mg/kg, enrofloxacin achieved peak concentrations of approximately 3 mg/L in blood and 3-4 µg/g in muscle tissue. After bath dosing for 5 h at an enrofloxacin concentration of 10 mg/L, peak concentrations were approximately 0.3 to 0.6 mg/L in blood and 0.4 to 1.0 µg/g in muscle tissue.

Conclusion: This study successfully demonstrated that oral administration of enrofloxacin and florfenicol can attain blood concentrations of both antibiotics that are sufficient to treat common freshwater bacterial infections. The findings of this study will enhance the ability of veterinary professionals to treat giant danio and related fish effectively, especially those suffering from common and emerging bacterial pathogens. Furthermore, the study achieved promising drug exposures in giant danio for bacterial pathogens relevant to fish, providing valuable information for future research in this area.

Figure 1. Concentration of florfenicol in the blood (a) and muscle (b) of giant danio (Devario aequipinnatus) following oral gavage administration of enrofloxacin. Animals were received an oral dose of 60 mg/kg florfenicol. The plot represents a visual predictive check which showed that the population PK model adequately described the central tendency and between subject variability of the observations. The markers are the observed concentrations. The thick black line represents the median and should reflect the central tendency of the observations. The 10th to 90th percentiles form the 80% prediction interval. Ideally, 10th of the observations should fall outside of this 80% prediction interval on either side. With a small number of observations per time-point, this sample size does not support a rigid interpretation of the prediction interval. However, both the 80% prediction interval and the inter-quartile range (25th to 75th percentiles) should reflect the variability of the observations.

Figure 2. Concentration of enrofloxacin in the blood (a) and muscle (b) of giant danio (Devario aequipinnatus) following oral gavage administration of enrofloxacin. Animals received an 8 mg/kg oral dose of enrofloxacin. Please see Fig. 1 for further explanations about the interpretation of this visual predictive check.

Figure 3. Concentration of enrofloxacin in the blood (a) and muscle (b) of giant danio (Devario aequipinnatus) following bath administration of enrofloxacin. Animals were placed in a bath of enrofloxacin at a concentration of 10 mg/L for 5 hours, then removed from the bath and euthanized between 0 and 48 hours after bath removal for blood and muscle collection. Please see Fig. 1 for further explanations about the interpretation of this visual predictive check.