Are antipseudomonal antibiotics really beneficial in acute respiratory exacerbations of cystic fibrosis?

Background: Although anti-pseudomonal antibiotics are routinely used in the treatment of acute respiratory exacerbations of adult cystic fibrosis (CF) , the specific efficacy of such treatment remains uncertain, the mechanism of action of these agents is not fully understood, and the role of sputum s usceptibility testing in clinical decision making is controversial. Aims: We investigated the relationship between susceptibility testing and c linical outcome in adult CF patients colonised with Pseudomonas aeruginosa. Methods: Sputum samples were collected before, during and after respiratory exacerbations from 31 admissions (17 patients). Sputum colony counts and M IC of P. aeruginosa were performed. Results: Sputum colony counts did not change significantly during or after intravenous (IV) antibiotic therapy. Clinical outcome parameters (lung func tion, 12-minute walking distance, sputum weight and quality of life) were c ompared with susceptibility of P. aeruginosa colonies isolated at admission to the antibiotics used, and no correlation was evident. There was no evid ence for the development of cross-resistance and there was no change in the proportion of mucoid colonies with therapy. Conclusions: While this study has a small patient sample size, it highlight s the inconsistency of the role of antipseudomonal drugs also shown in othe r similar studies. The presence of P. aeruginosa in sputum of acutely ill C F patients prompts us to prescribe IV antipseudomonal drugs. If this approa ch was valid, we would expect to find a reduction in sputum colony counts a nd improvement in clinical parameters with the use of antibiotics to which the organisms were sensitive. The fact that such a relationship cannot be c onsistently demonstrated in this and other studies suggests that the use of antipseudomonal therapy in these patients requires more critical bacteriol ogical and clinical evaluation.