PHARMACOKINETICS OF DOXYCYCLINE IN BROILER-CHICKENS

Doxycycline was given to two groups of eight chickens at a dose of 20 mg/kg of body weight, intravenously (i.v.) or orally. Plasma concentra tion was monitored serially for 12 h after each administration. Anothe r group of 30 chickens was given 20 mg/kg orally every 24 h for 4 days , and plasma and tissue concentrations determined serially after the l ast administration. Concentrations of doxycycline were measured using high-performance liquid chromatography. Pharmacokinetic variables were calculated, using a two-compartment open model. The elimination half- life and the mean residence time for plasma were 6.03 +/- 0.45 and 7.4 8 +/- 0.38 h, respectively, after oral administration and 4.75 +/- 0.2 1 and 2.87 +/- 0.11 h, respectively, after i.v. administration. After single oral administration, doxycycline was absorbed rapidly, with T(m ax) of 0.35 +/- 0.02 h. Maximum plasma concentration was 54.58 +/-2.44 mug/ml. Oral bioavailability of doxycycline was found to be 41.33 +/- 2.02%. Doxycycline was widely distributed in tissues and considerable concentrations were found following oral administration of 20 mg/kg o n four successive days. The results indicate that doxycycline concentr ations were cleared slowly and were at or below the accepted drug tole rance levels in the marker tissues within 5 days after dosing.