[Penetration of netilmicin into respiratory secretions]

Aminoglycosides are often used in the treatment of severe Gram-negative infections, particularly those involving the respiratory tract. The purpose of this study was to evaluate the penetration of netilmicin into bronchial secretions. In 8 tracheostomized patients samples of bronchial secretions were taken at intervals through the tracheostomy cannula after intramuscular injection of netilmicin 2 mg/kg bodyweight. Concentrations of the drug were measured in bronchial secretions and in blood samples taken simultaneously, using the agar diffusion method (Grove and Randall procedure). The results showed significant penetration of netilmicin, with a mean bronchial peak reaching 3.4 micrograms/ml 1 h after the injection. Elimination was slow, with a mean residual level of 2 micrograms/ml at 6 hours. The bronchial to serum levels ratio was high (greater than 30% at 1 hour). Individual variations in both serum and bronchial levels were noted; they were unrelated to the underlying pathology. However, changes in bronchial concentrations correlated with changes in serum concentrations, which suggests passive diffusion across the blood-bronchoalveolar barrier. The fluctuations in bronchial levels and the usually low bronchial concentrations of aminoglycosides previously reported are discussed in relation to the methods used.