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 AUCmilk/AUCplasma 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.