Macedonian Veterinary ReviewThe pharmacokinetics of doxycycline was investigated in force-fed and normally fed ducks after single intravenous (i.v.) and oral (p.o.) administration at a dose of 15 mg/kg bw. Serum concentrations of the drug were determined by the HPLC method. Pharmacokinetic parameters were calculated using compartmental analysis. Serum concentrations of doxycycline after i.v. administration in both groups were not statistically different. The values of half-lives were 5.82±1.85 h and 6.06±5.51 h in normal and force-fed birds. The total body clearance was respectively 0.40±0.05 L/h/kg and 0.34±0.10 L/h/kg, and volume of distribution (V ss ) was 2.80±0.85 L/kg and 2.18±0.89 L/kg. After p.o. administraton the maximum serum levels in the control group were 0.70±0.12 μg/mL and in force-fed birds were 1.93±0.32 μg/mL, measured at 2.95±0.60 h and 1.45±0.24 h, respectively. The values of absolute bioavailability were 18.89±6.48% and 37.58±13.63%. Longer doxycycline retention in force-fed ducks was registered. Our data can be accepted as an information for possible prolonged retention of doxycycline in force fed ducks compared to normally fed ones.