Pharmacokinetics of doxycycline after a single intravenous, oral or intramuscular dose in Muscovy ducks (Cairina moschata)

The pharmacokinetics of doxycycline in ducks were investigated after a single intravenous (IV), intramuscular (IM) or oral (PO) dose at 20 mg/kg body weight. 2. The concentrations of doxycycline in plasma samples were assayed using a high performance liquid chromatography method, and pharmacokinetic parameters were calculated using a non-compartmental model. 3. After IV administration, doxycycline had a mean (±SD) distribution volume (Vz) of 1761.9 ± 328.5 ml/kg and was slowly eliminated with a terminal half-life (t₁/₂λz) of 21.21±1.47 h and a total body clearance (Cl) of 57.51 ± 9.50 ml/h/kg. Following PO and IM administration, doxycycline was relatively slowly absorbed - the peak concentrations (Cmax) were 17.57 ± 4.66 μg/ml at 2 h and 25.01 ± 4.18 μg/ml at 1.5 h, respectively. The absolute bioavailabilities (F) of doxycycline after PO and IM administration were 39.13% and 70.71%, respectively. 4. The plasma profile of doxycycline exhibited favourable pharmacokinetics characteristics in Muscovy ducks, such as wide distribution, relatively slow absorption and slow elimination, though oral bioavailability was low.