Study objective: To compare clinical and microbiologic outcomes in adults without cystic fibrosis who had Pseudomonas aeruginosa bronchial colonization and were receiving inhaled colistin or colistin plus tobramycin with those who were receiving inhaled tobramycin as outpatient treatment.
Design: Prospective, observational cohort study.
Setting: Referral pneumology service at a tertiary university care hospital.
Patients: Eighty-one Caucasian adults without cystic fibrosis who received 97 courses of inhaled colistin alone, colistin plus tobramycin, or inhaled tobramycin alone as outpatient treatment of P. aeruginosa bronchial colonization between January 2004 and December 2008.
Measurements and main results: The frequency and duration of hospitalizations for respiratory exacerbations were the primary outcomes compared among treatment groups. Secondary outcomes were emergence of bacterial resistance, antibiotic use during admission, emergence of other opportunistic microorganisms, achievement of sustained P. aeruginosa eradication in the airways, and mortality, as well as safety and changes in respiratory function. No significant differences between colistin and tobramycin were found in the mean number of hospital admissions, duration of hospitalizations, duration of antibiotic treatment, adverse events, mortality, or emergence of other opportunistic microorganisms. Emergence of resistance to colistin was lower than resistance to tobramycin (hazard ratio 0.09, 95% confidence interval [CI] 0.03-0.32). Patients treated with both inhaled antibiotics had fewer days of hospitalization and fewer days of antibiotic use than those treated with tobramycin alone (relative risk [RR] 0.33, 95% CI 0.10-1.12, and RR 0.27, 95% CI 0.08-0.93, respectively).
Conclusion: Results with colistin were similar to those with tobramycin for inhaled treatment of P. aeruginosa colonization in this population; however, combined use of colistin and tobramycin appeared to be associated with fewer days of hospitalization and shorter duration of antibiotic treatment. Prospective, double-blind, placebo-controlled trials of outpatient nebulized antibiotics, especially colistin plus tobramycin, should be performed to ascertain the efficacy of this therapy for treatment of P. aeruginosa colonization in patients without cystic fibrosis.