Pharmacokinetic interaction of enrofloxacin/trimethoprim combination following single-dose intraperitoneal and oral administration in rats

The pharmacokinetic interaction of enrofloxacin and trimethoprim was evaluated after single-dose intraperitoneal or oral co-administration in rats. Plasma concentrations of the two drugs were determined by high-performance liquid chromatography. Following intraperitoneal combination, a significant (P < 0.05) increase in mean values of plasma half-life (t_1/2) and maximum plasma concentration (C_max) was observed for enrofloxacin and trimethoprim, respectively. There was a significant (P < 0.05) increase in mean values of area under the plasma drug concentration versus time from time zero to infinity (AUC_0-∞) and C_max between combined oral doses (10, 30 and 100 mg/kg) of both antibacterial drugs. Also, after oral conjugation a significant difference in mean values of MRT_0-∞ was observed between lower (10 mg/kg) and higher (100 mg/kg) doses of both drugs. A significant increase in pharmacokinetic parameters of both drugs in combined intraperitoneal and oral doses indicated pharmacokinetic interaction of enrofloxacin and trimethoprim. Further study is recommended in other species of animals.