Nebulization and anti-Pseudomonas aeruginosa activity of colistin

Colistin aerosols are frequently administered to patients with cystic fibrosis. However, questions arise concerning the effect of both jet and ultrasonic nebulizers on the properties of the drug. The aim of this study was to characterize the anti-Pseudomonas aeruginosa (PA) activity of colistin after jet (Pari LL) and ultrasonic (DP100) nebulization. A bench study was performed by capturing the aerosols, determining the drug mass, and assessing its anti-PA activity. Because the inhaled mass of colistin had to be entirely recovered for the bacteriological study, it was assessed by isotopic methods, mixing the drug with a 99mTc-labelled tracer and demonstrating that 99mTc activity accurately predicted the mass of colistin. Colistin was extracted from the filters and its antibiotic activity was determined using the method employed for the study of the bacteriostatic and bactericidal power of serum on the ATCC 27853 PA strain. The postnebulization minimum inhibitory concentrations (MIC) were 1.9 micrograms.mL-1 with DP100 and 0.5 microgram.mL-1 with Pari LL. These values were less than two dilutions different from the 1 microgram.mL-1 MIC of non-nebulized colistin. We conclude that neither jet nebulization nor ultrasonic nebulization alter the antibiotic properties of colistin and that both systems can be used to nebulize colistin.