Physicochemical characterization and pharmacokinetics in broiler chickens of a new recrystallized enrofloxacin hydrochloride dihydrate

Enrofloxacin, a key antimicrobial agent in commercial avian medicine, has limited bioavailability (60%). This prompted its chemical manipulation to yield a new solvate‐recrystallized enrofloxacin hydrochloride dihydrate entity (enro_C). Its chemical structure was characterized by means of mass spectroscopy, Fourier transformed infrared spectroscopy, X‐ray powder diffraction, and thermal analysis. Comparative oral pharmacokinetics (PK) of reference enrofloxacin (enro_R) and enro_C in broiler chickens after oral administration revealed noticeable improvements in key parameters and PK/PD ratios. Maximum serum concentration values were 2.61 ± 0.21 and 5.9 ± 0.42 μg/mL for enro_R and enro_C, respectively; mean residence time was increased from 5.50 ± 0.26 h to 6.20 ± 0.71 h and the relative bioavailability of enro_C was 336%. Considering C_max/MIC and AUC/MIC ratios and the MIC values for a wild‐type Escherichia coli O78/H12 (0.25 μg/mL), optimal ratios will only be achieved by enro_C (C_max/MIC = 23.6 and AUC/MIC = 197.7 for enro_C; vs. C_max/MIC = 10.4 and AUC/MIC = 78.1 for enro_R). Furthermore, enro_C may provide in most cases mutant prevention concentrations (C_max/MIC ≥ 16). Ready solubility of powder enro_C in drinking water at concentrations regularly used (0.01%) to provide an additional advantage of enro_C in the field. Further development of enro_C is warranted before it can be recommended for clinical use in veterinary medicine.