Pharmacokinetic disposition of marbofloxacin after intramuscular administration in estuarine crocodiles (Crocodylus porosus)

To date, the pharmacokinetics of fluoroquinolones in estuarine crocodiles (Crocodylus porosus) have been reported for enrofloxacin but not for marbofloxacin (MBF), which is a broad-spectrum antibiotic used only in veterinary medicine. This study investigated the pharmacokinetics of MBF after intramuscular administration at two difference dosages (2 and 4 mg/kg body weight) in estuarine crocodiles and estimated pharmacokinetic/pharmacodynamic (PK/PD) surrogate parameters for the optimization of dosage regimens. Ten treated estuarine crocodiles were divided into two groups (n = 5) using a randomization procedure according to a parallel study design. Blood samples were collected at assigned times up to 168 h. MBF plasma samples were cleaned up using liquid-liquid extraction and analyzed using a validated high-performance liquid chromatography method with fluorescence detection. A non-compartment approach was used to fit the plasma concentration of MBF vs time curve for each crocodile. The plasma concentrations of MBF were quantifiable for up to 168 h in both groups. The elimination half-life values of MBF were long (33.99 and 39.28 h for 2 and 4 mg/kg, respectively) with no significant differences between the groups. The average plasma protein binding of MBF was 30.85%. According to the surrogated PK/PD parameter (AUC(0-24)-to-MIC ratio >100-125), the 2 and 4 mg/kg dosing rates should be effective for bacteria with MIC values lower than 0.125 mu g/mL and 0.35 mu g/mL, respectively.