Basis for nebulized antibiotics: Droplet characterization and in vitro antimicrobial activity versus Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa

The aims of this study were to (1) quantify the particle size characteristi cs of several antibiotics considered suitable for aerosol therapy after aer osolization with the PARI IS/2 nebulizer (Pari GmbH, Sarnberg, Germany) and (2) determine the degree to which in vitro antimicrobial activity of these antibiotics is maintained after nebulization. The aerosolized drugs were t obramycin sulfate, streptomycin, and imipenem, with saline solution as the control. Mean mass aerodynamic diameter of the nebulized drugs was 3.25 mu m for tobramycin, 2.26 mu m for imipenem, and 2.38 mu m for streptomycin. I n vitro tests showed that tobramycin and imipenem were unaltered in their b acteriostatic activity against strains of Escherichia coli (American Type C ulture Collection [ATCC] 25922) and Staphylococcus aureus (ATCC 29213) as w ell as against Pseudomonas aeruginosa (ATCC 27853) with minimal inhibitory concentration (MIC) values less than 0.3 mu g/mL. Nebulized streptomycin sh owed significantly higher MIC values against P. aeruginosa (ATCC 27853). Th ese results suggest that tobramycin and imipenem may be prescribed as an ae rosol generated by jet nebulization (PARI IS/2) to treat S. aureus, E. coli , and P. aeruginosa infections without any risk of altering the drugs(1) mi nimum bacteriostatic activity by the nebulization process. Aerosolization o f streptomycin with this nebulizer may not be as effective against P. aerug inosa because it seems to alter the bacteriostatic activity.