A pharmacokinetic investigation of florfenicol as an alternate treatment for chlamydiosis in the koala (Phascolarctos cinereus)

Abstract

Florfenicol (FFC) as Nuflor™ was investigated as a treatment of chlamydiosis in koalas. Chlamydiosis is considered the important infectious disease of koalas, causing significant morbidity and mortality. A HPLC-UV assay of FFC in koala plasma was developed with a lower limit of quantification (LLOQ) of 0.3 µg/mL. Florfenicol was administered at 20 mg/kg subcutaneously (SC) once (n=3), 10 mg/kg intravenously (IV) once (n=3) and 5 mg/kg IV every 48 hours thrice (n=3). Plasma FFC concentrations were compared with minimum inhibitory concentrations of FFC against Chlamydia pecorum in vitro. The clinical records and outcomes of 19 wild koalas treated with FFC are reviewed and presented in summary. The mean (n=3) maximum concentration of FFC in plasma (Cmax) following 20 mg/kg SC was 1.2 μg/ml at Tmax of 4 hours, with concentrations < LLOQ by 24 hours. Following IV administration at 10 mg/kg, FFC was noted to persist at potentially useful concentrations in plasma for a practical dosing interval in 2/3 koalas with a mean, (n= 3) FFC plasma concentration of 19 μg/mL at 24 hours. A prolonged terminal elimination phase appears to exist following intravenous administration. The proportion of FFC binding to koala plasma proteins in vitro is 13%. Florfenicol was poorly tolerated by koalas following administration of multiple subcutaneous dosages from 5 – 20 mg/kg. Koalas were tolerant of single FFC treatments of 20 mg/kg SC, 10 mg/kg IV and three consecutive dosages of 5 mg/kg IV. A single intravenous dosage of FFC at 10 mg/kg may be useful to assist control of some bacterial infections, however caution is recommended if administering Nuflor™ to koalas via this route. Florfenicol cannot be recommended as an alternative to chloramphenicol for the treatment of chlamydiosis in koalas.