Pharmacokinetics of doxycycline in pigs following oral administration in feed.

Doxycycline medicated feed was administered to healthy fattening pigs for an 8-day period either for 1 h every 12 h or ad libitum. The average dosage regimen ranged between 11.8 and 13.3 mg/kg/day. Doxycycline concentrations were determined in plasma, lung and nasal mucosa using a high performance liquid chromatography assay (HPLC). The agreement between the doxycycline HPLC assay and a bioassay was also assessed in plasma. Following the multiple medicated feed administration every 12 h, the plasma concentrations were best described by a one-compartmental model with first-order absorption. Steady-state plasma concentrations ranged between 0.7 and 1 microgram/mL. The mean accumulation factor and elimination half-life were, respectively, 1.8 +/- 0.4 and 5.9 +/- 1.0 h. Following ad libitum administration of medicated feed, steady-state plasma concentrations ranged between 0.9 and 1.5 micrograms/mL. At the end of the treatment, the doxycycline lung and nasal mucosa concentrations were 1.7 +/- 0.4 micrograms/g and 2.9 +/- 0.6 micrograms/g, respectively. These data validate the dosage regimen tested in order to control pig respiratory infections, provided that controlled clinical studies are confirmatory.