Comparative Pharmacokinetics of Enrofloxacin After Subcutaneous Administration of a Novel in situ Gel Forming Preparation and a Conventional Product to Rabbits

BACKGROUND: Frequent drug dosing and animal handling are usually required in conventional antimicrobial therapy but sustained release formulations can improve compliance. OBJECTIVES: This study aimed to evaluate the pharmacokinetic (PK) parameters of a novel sustained release enrofloxacin (ENR) hydrogel in comparison to a conventional ENR formulation in rabbit animal model. METHODS: A total of 20 rabbits were randomly divided into three groups and received a single dose of ENR or blank by subcutaneous (SC) injection as following: Group 1 (n=8) received ENR (10 mg/kg) using a conventional product (Enrovet®); Group 2 (n=8) received ENR (33.3 mg/kg) using a hydrogel formulation; and Group 3 or control group (n=4) received equal volumes of a blank hydrogel formulation. Blood samples were collected at different time points post-dosing. ENR concentrations in plasma were estimated by high-performance liquid chromatographic (HPLC) method and PK parameters were calculated using a non-compartmental analysis. RESULTS: The ENR hydrogel released the drug in a sustained manner with mean residence time (MRT) of 78.4 ± 15.3 h, which was significantly more than that of the conventional formulation (7.39 ± 2.37 h, P 0.05). However, maximal plasma concentration (Cmax) for ENR hydrogel (1.41 ± 0.76 μg/mL) was significantly less than that of the conventional product (2.86 ± 0.79 μg/mL). The relative bioavailability (Frel) was not significantly different between the two formulations. CONCLUSIONS: The hydrogel formulation significantly increased the MRT of ENR. Hence, it could be a promising delivery system to prolong the pharmacological activity of ENR in animals and enhance compliance.