The penetration of aminoglycosides into the alveolar lining fluid of rats. The effect of airway inflammation.

The concentration-time profile of gentamicin and tobramycin in the alveolar lining fluid (ALF) of rats was determined after intravenous bolus injection using bronchoalveolar lavage (BAL). BAL can be used for evaluating the penetration of both aminoglycosides into the ALF if highly sensitive detection methods are used, and an endogenous marker (urea) can be applied to avoid the unpredictable dilutional effect of the lavage procedure. The concentration of gentamicin and tobramycin in ALF reached a peak after 5 and 10 min, respectively, and remained high when plasma concentrations were declining, suggesting an accumulation reservoir in the lung acini. The ratio of the AUC of the concentration-time profile in ALF and plasma was 0.67 and 0.45 for gentamicin and tobramycin, respectively. The penetration of both aminoglycosides into the ALF was significantly higher after induction of airway inflammation by inhalation of endotoxin. The ratio of the AUC in ALF and plasma in the endotoxin-exposed animals was 0.76 and 0.55 for gentamicin and tobramycin, respectively. The ratio of the AUC of the concentration-time profile of gentamicin in ALF to that of tobramycin was 1.27 without inflammation and 1.44 after endotoxin exposure. Thus, both with and without inflammation, gentamicin penetrates better into the ALF than does tobramycin.