Pharmacokinetic and milk penetration of a difloxacin long-acting poloxamer gel formulation with carboxy-methylcellulose in lactating goats.

The single-dose disposition kinetics of difloxacin were determined in clinically normal lactating goats (n=6) after subcutaneous administration of a long-acting poloxamer 407 gel formulation with carboxy-methylcellulose (P407-CMC). Difloxacin concentrations were determined by high performance liquid chromatography with fluorescence detection. The concentration-time data were analysed by non-compartmental kinetic methods. Plasma and milk elimination half-lives after P407-CMC dosing were 35.19 h and 33.93 h, respectively. With this formulation, difloxacin achieved maximum plasma concentrations of 2.67±0.34 mg/L at 2.92±1.20 h and maximum milk concentrations of 2.31±0.35 mg/L at 4.00±0.00 h. The area under the curve (AUC) ratio AUC(milk)/AUC(plasma) was 0.89 after P407-CMC administration. It was concluded that a 15 mg/kg dose of difloxacin within P407-CMC would be effective against mastitis pathogens with a minimum inhibitory concentration (MIC)≤0.12 mg/L.