Clinical pharmacokinetics of norfloxacin-glycine acetate after intravenous and intramuscular administration to horses

The pharmacokinetic properties of norfloxacin-glycine acetate (NFLXGA) were determined in six horses following a single intravenous (i.v.) and intramuscular (i.m.) dose of 4 mg kg ^-1 body weight. Following i.v. and i.m. administration, the plasma drug concentrations were best fitted by an open two-compartment model with a rapid distribution phase. After i.v. NFLXGA administration, the distribution (t _1/2α ,) and elimination half-life (t _1/2β ) were 0.42 (0.05) and 5.44 (1.36) h. The volume of distribution of NFLXGA at steady state (Vd _ss ) was 2.19 (0.53) L kg ^-1 . After NFLXGA i.m. administration, the maximal absorption concentration (C _max ) was 0.44 (0.04) μg ml ^-1 at 0.86 (0.15) h (T _max ). The mean absorption (t _1/2ka ) and elimination half-life (t _1/2β ) of NFLXGA were 0.27 (0.07) and 9.47 (2.24) h, respectively. The mean systemic bioavailability (F) following i.m. administration was 55 (12)%. The optimal dosage for each administration route was calculated from the pharmacokinetic data on the basis of the area under the inhibitory plasma concentration-time curve (AUIC) every 24 h and was found to be 13.36 and 7.35 mg kg ^-1 for i.m. and i.v. administration, respectively.