Ovine pulmonary transit of tetracycline and minocycline

Following cannulation of the right external jugular vein and the efferent duct of the right caudal mediastinal lymph node (the caudal end of this node was ligated to cut off the inflow of systemic lymph, i.e., 90%–95% of the efferent lymph was of pulmonary origin), sheep were given either tetracycline or minocycline as single doses of 5 mg/kg body weight infused intravenously over 30 min. Venous blood plasma and pulmonary lymph collected contemporaneously before infusion and from 5 min to 24 hr postinfusion were assayed by a well-agar diffusion method using Bacillus cereus . Peak concentrations of both drugs were observed in both plasma and lymph at 5 min postinfusion. Tetracycline penetrated into the lymph better than minocycline (percent penetration 67.3% cf. 38.2%). The concentration of tetracycline was significantly higher in lymph during and 5 min postinfusion ( p < 0.01), a factor that may be of importance when selecting a tetracycline for the treatment of a pulmonary infection.