Bioavailability, pharmacokinetics, and plasma concentration of tetracycline hydrochloride fed to swine

A 2 X 2 crossover design trial was conducted in gilts to determine the bioavailability and pharmacokinetics of tetracycline hydrochloride. The bioavailability of tetracycline hydrochloride administered orally to fasted gilts was approximately 23%. After intravascular administration, the disposition kinetics of tetracycline in plasma were best described by a triexponential equation. The drug had a rapid distribution phase followed by a relatively slow elimination phase, with half-life of 16 hours. Its large volume of distribution (4.5 +/- 1.06 L/kg) suggested that tetracycline is distributed widely in swine tissues. Total body clearance was 0.185 +/- 0.24 L/kg/h. Other pharmacokinetic variables were estimated. In a second trial, 3 gilts were fed a ration containing 0.55 g of tetracycline hydrochloride/kg of feed. Resulting plasma concentration of tetracycline was determined at selected times during 96 hours after exposure to the medicated feed. Plasma drug concentration peaked (0.6 micrograms/ml) at 72 hours after access to the medicated feed.