As a novel formulation of enrofloxacin, the toxicity of enrofloxacin microemulsion was unknown. The present study was conducted to determine the median lethal dose (LD₅₀) of enrofloxacin microemulsion by using the acute toxicity test in mice. Based on the dose range of the pretest, mice in the group receiving the enrofloxacin microemulsion were intragastrically administered the dose levels of 1320.0, 1056.0, 844.8, 675.84, 540.67 and 432.6 mg/kg of body weight, respectively. LD₅₀ calculated by Bliss method was 740.08 mg/kg, and 95% confidence limit of LD₅₀ was 647.11~844.87 mg/kg, which indicated enrofloxacin microemulsion could be labeled as the hazard category 4 according to GHS and be considered as a low toxicity drug.

Key words: Acute toxicity test, Enrofloxacin, Median lethal dose, Mice, Microemulsion