Clinically normal koalas (n = 6) received a single dose of intravenous enrofloxacin (10 mg/kg). Serial plasma samples were collected over 24 h, and enrofloxacin concentrations were determined via high‐performance liquid chromatography. Population pharmacokinetic modeling was performed in S‐ADAPT. The probability of target attainment (PTA) was predicted via Monte Carlo simulations (MCS) using relevant target values (30–300) based on the unbound area under the curve over 24 h divided by the minimum inhibitory concentration (MIC) (fAUC0–24/MIC), and published subcutaneous data were incorporated (Griffith et al., 2010). A two‐compartment disposition model with allometrically scaled clearances (exponent: 0.75) and volumes of distribution (exponent: 1.0) adequately described the disposition of enrofloxacin. For 5.4 kg koalas (average weight), point estimates for total clearance (SE%) were 2.58 L/h (15%), central volume of distribution 0.249 L (14%), and peripheral volume 2.77 L (20%). MCS using a target fAUC0–24/MIC of 40 predicted highest treatable MICs of 0.0625 mg/L for intravenous dosing and 0.0313 mg/L for subcutaneous dosing of 10 mg/kg enrofloxacin every 24 h. Thus, the frequently used dosage of 10 mg/kg enrofloxacin every 24 h subcutaneously may be appropriate against gram‐positive bacteria with MICs ≤ 0.03 mg/L (PTA > 90%), but appears inadequate against gram‐negative bacteria and Chlamydiae in koalas.