Lung distribution and pharmacokinetics of aerosolized tobramycin

Aminoglycosides are commonly used in the treatment of nosocomial pneumonia in association with beta-lactams. Unfortunately, penetration of intravenously administered aminoglycosides into the lung tissue remains low. In animal models, aerosolization of these drugs provides high lung concentrations and low serum levels. Three-hundred milligrams of tobramycin and 1 ml of 99mTc-DTPA were administered via a pneumatic nebulizer to five healthy volunteers and to five mechanically ventilated patients. Lung scintigraphy was then performed, and plasma and urine pharmacokinetics were studied. In a second group of patients undergoing thoracic surgery, 300 mg of tobramycin alone were administered in the same way; a fragment of healthy lung was then removed, and tobramycin was measured. In the first group, the scintigraphy showed radioactivity distribution in the whole lungs both in healthy volunteers and in ventilated patients. Urine samples contained 5.5% of the initial amount of tobramycin. The mean serum half-life of tobramycin was 8.96 h in healthy volunteers and 11.23 h in ventilated patients. In the second group, mean lung tissue concentrations were 5.5 and 3.61 micrograms/g, respectively, 4 and 12 h after nebulization, respectively. Aerosolization of tobramycin thus produced high lung concentrations and low serum levels.