Pharmacokinetic Studies of an In Situ Forming Gel System for Controlled Delivery of Enrofloxacin In Pigs

The objective of this study was to evaluate the pharmacokinetic characteristics of enrofloxacin (ENR) in situ forming gel in pigs following a single intramuscular administration. Twelve healthy pigs were randomly divided into two groups (6 pigs per group), then administered 20 mg/kg body weight (b.w.) ENR in situ forming gel and 5 mg/kg b.w. ENR conventional injection respectively. Highperformance liquid chromatography was used to determine ENR plasma concentrations. The important pharmacokinetic parameters of ENR in situ forming gel and conventional injection in pigs were as follows: MRT (mean residence time) 49.39 ± 8.97 h verse 11.75 ± 0.90 h, Cmax (maximal concentration) 1.71 ± 0.24 μg/mL verse 1.76 ± 0.32 μg/mL, t1/2λz (terminal elimination half-life) 42.92 ± 9.80 h verse 9.17 ± 0.61 h. Results suggest that the Cmax of ENR in situ forming gel was in the range of ideal bactericidal concentration, and values of t1/2λz and MRT were greatly extended, which could maintain the effective blood drug concentrations for a long time. Therefore, the pharmacokinetic characteristics of ENR in situ forming gel in pigs following a single i.m. administration were ideal. And the in situ forming gel system seems to be a feasible approach for ENR long-acting delivery.