Pharmacokinetics of two dosing forms of a recrystallized enrofloxacin as hydrochloride dihydrate in tilapia (Oreochromis niloticus × Oreochromis mossambicus) E Estrada-San Agustín 1 & L Gutiérrez 1 & M Bernad 2 & H Castillo-Juárez 3 & S Sánchez 4 & H Sumano 1 Received: 4 September 2018 /Accepted: 24 March 2019/ # Springer Nature Switzerland AG 2019 Abstract A recrystallized solvate of enrofloxacin in the form of hydrochloride dihydrate (enro-C) has shown a greater bioavailability in other species and a higher solubility in water compared to standard enrofloxacin. This led to define the pharmacokinetics (PK) of enro-C in tilapia (Oreochromis niloticus × Oreochromis mossambicus), when administered as in-feed medication, either by the addition of enro-C during food pelleting (T2) or by the coating of pre-manufactured pellets with a gelatin suspension containing enro-C (T1). T1 and T2 were both prepared with 3000 mg of enro-C/kg of feed, and a total dose of 10 mg/kg based on feed consumption. The trial was carried out in fresh water tanks, collecting blood samples twelve times during 70 h (three repetitions with five tilapias per sampling time). Maximum plasma concentrations (C MAX ) for T1 and T2 were 1.35 ± 0.55 μg/mL and 1.92 ± 0.26 μg/mL, respectively. The time to achieve C MAX (T MAX ) occurred almost simultaneously at 6.5 h. The area under the plasma vs time concentrations (AUC 0-24 ) were 25.41 ± 24 μg/mL/h and 57.91 ± 30 μg/mL/h for T1 and T2, respectively. MIC data from available literature indicate that PK/PD ratios (C MAX /MIC 90 and AUC 0-24 / MIC 90 ) are higher in T2 compared to T1 in tilapia. Results indicate that the customary dose of enrofloxacin (10 mg/kg) using enro-C reaches, in particular, higher values of C MAX and AUC 0-24 . Thus, based on these results, it is feasible to propose enro-C for the treatment of bacterial diseases in tilapia, preferably as was done in T2. However, before this happens, toxicity and drug-residue studies, as well as environmental and public health issues, must be resolved. Keywords Tilapia . Enrofloxacin . Enro-C . Pharmacokinetics . PK/PD ratios Aquaculture International https://doi.org/10.1007/s10499-019-00371-9 * H Sumano sumano@unam.mx Extended author information available on the last page of the article