# Pharmacokinetic Characteristics of Florfenicol in Freshwater Crocodiles (Crocodylus siamensis) After Intramuscular Administration

## TL;DR

This study examines how the antibiotic florfenicol behaves in the blood of freshwater crocodiles after injection, providing key data for safe and effective treatment.

## Contribution

The study provides the first pharmacokinetic data for florfenicol in freshwater crocodiles, enabling better antimicrobial dosing in this species.

## Key findings

- Florfenicol was well absorbed and remained in the bloodstream for extended periods in crocodiles.
- Plasma concentrations exceeded MIC90 values for several bacterial pathogens, suggesting effective treatment potential.
- Elimination half-lives were long but not significantly different between the two tested doses.

## Abstract

Pharmacokinetic information on antimicrobial use in reptiles is extremely limited. Often, drug dosages and approaches are extrapolated from other animal species, which can lead to ineffective or unsafe treatments. This study investigated the disposition kinetics of florfenicol after a single intramuscular injection in freshwater crocodiles based on two dosages. Based on the results, the drug was well absorbed, was prolonged in the bloodstream, and reached levels expected to control bacterial infections. These findings have provided essential baseline information that should help to ensure more effective, accurate, and safe antimicrobial use in freshwater crocodiles.

Florfenicol (FFC) is widely used to treat bacterial infections in veterinary medicine; however, its pharmacokinetic characteristics in reptiles remain limited. This study investigated the pharmacokinetic profiles of FFC after intramuscular (IM) injection at doses of 20 or 30 mg/kg body weight (b.w.) in freshwater crocodiles (Crocodylus siamensis). A sample of 10 healthy crocodiles was randomly divided into two groups (n = 5 for each group) according to a parallel study design. Blood samples were obtained from pre-dose to 168 h post-administration. Plasma FFC concentrations were quantified using high-performance liquid chromatography with diode array detection (HPLC-DAD) and analyzed by non-compartmental analysis. The mean maximum plasma concentrations of FFC were 4.05 µg/mL and 6.11 µg/mL for the 20 and 30 mg/kg b.w. doses, respectively. The mean elimination half-lives of FFC were long but not significantly different (51 h). The average plasma protein binding was 37.15%. Based on the pharmacokinetics/pharmacodynamics (PK/PD) index, a single dose of FFC via IM elicited plasma concentrations above the MIC90 values reported for several susceptible bacterial pathogens. Consequently, both dose levels provided plasma exposure consistent with previously reported reference MIC values. However, further PK/PD and multiple-dose investigations are needed to refine species-specific dosage regimens.