Absorption of enrofloxacin and marbofloxacin after oral and subcutaneous administration in diseased koalas (Phascolarctos cinereus)

Koalas (n = 43) were treated daily for up to 8 weeks with enrofloxacin: 10 mg/kg subcutaneously (s.c.), 5 mg/kg s.c., or 20 mg/kg per os (p.o.); or marbofloxacin: 1.0-3.3 mg/kg p.o., 10 mg/kg p.o. or 5 mg/kg s.c. Serial plasma drug concentrations were determined on day 1 and again at approximately 2 weeks, by liquid chromatography. The median (range) plasma maximum concentrations (C(max) ) for enrofloxacin 5 mg/kg s.c. and 10 mg/kg s.c. were 0.83 (0.68-1.52) and 2.08 (1.34-2.96) μg/mL and the median (range) T(max) were 1.5 h (1-2) and 1 h (1-2) respectively. Plasma concentrations of orally dosed marbofloxacin were too low to be quantified. Oral administration of enrofloxacin suggested absorption rate limited disposition pharmacokinetics; the median (range) C(max) for enrofloxacin 20 mg/kg p.o. was 0.94 (0.76-1.0) μg/mL and the median (range) T(max) was 4 h (2-8). Oral absorption of both drugs was poor. Plasma protein binding for enrofloxacin was 55.4 ± 1.9% and marbofloxacin 49.5 ± 5.3%. Elevations in creatinine kinase activity were associated with drug injections. Enrofloxacin and marbofloxacin administered at these dosage and routes are unlikely to inhibit the growth of chlamydial pathogens in vivo.