Age-related changes in the pharmacokinetics of marbofloxacin after intravenous administration in goats

The pharmacokinetics of marbofloxacin was studied in adult goats and 1-, 3- and 6-weeks-old kids after single dose i.v. dose of 2 mg/kg body weight. Drug concentration in plasma was determined by high-performance liquid chromatography (HPLC) and the data collected were subjected to compartmental kinetic analysis. Volume of distribution was relatively high in adult goats (Vss = 1.31 L/kg), and increased with age (Vss = 0.92 L/kg, 0.95 L/kg and 1.00 L/kg, in 1-, 3- and 6-weeks-old kids respectively). Total body clearance (Cl) also increased with age from 0.080 L/kg.h (1-week-old) to 0.097 L/kg.h (3-weeks-old), 0.18 L/kg.h (6-weeks-old) and 0.23 L/kg.h (adult goats). As a consequence of increased body Cl, area under the plasma concentration vs. time curve decreased with age (AUC = 27.46 microg.h/mL, 22.61 microg.h/mL, 11.86 microg.h/mL and 8.44 microg.h/mL in 1-, 3-, 6-weeks-old kids and adults, respectively) and a longer elimination half-life was found during the first 3 weeks of age (t1/2beta = 9.66 h, 8.25 h, 6.44 h and 7.18 h, in 1-, 3-, 6-weeks-old kids and adults, respectively). Mean residence time decreased with age from 11.86 h in 1-week-old kids to 9.63 h (3 weeks), 5.76 h (6 weeks) and 5.06 h in adult goats.