Aztreonam in patients with acute purulent exacerbations of chronic bronchitis: failure to prevent emergence of pneumococcal infections.

A group of 36 patients, all requiring hospital admission because of acute purulent exacerbations of chronic bronchitis, were treated with 1 or 2 g intramuscular injections of aztreonam for ten days. Patients with Streptococcus pneumoniae infections were excluded from the study. Sputum cultures before treatment revealed the other usual respiratory pathogens but repeat cultures on days 3, 10 and 17 sometimes yielded Str. pneumoniae, occasionally combined with Haemophilus influenzae or Branhamella catarrhalis. Ten patients had to be given other antimicrobial agents for Str. pneumoniae infections which developed during the study or follow-up periods. Pseudomonas aeruginosa failed to respond well to aztreonam. All the H. influenzae strains were sensitive to aztreonam (MIC 0.25 mg/l, or less) but all strains of Str. pneumoniae were resistant (MIC greater than 32 mg/l). Ps. aeruginosa strains were moderately resistant (MIC generally 4-16 mg/l) and Bran. catarrhalis strains only moderately sensitive (MICs generally 0.5-4 mg/l). Peak serum concentrations averaging approximately 37 mg/l were observed after the 1 g injections (55 mg/l after 2 g) and the corresponding mean peak concentrations in the sputum were 1.3 mg/l and 2.5 mg/l, respectively. The penetration from blood to sputum was thus approximately 3.5% and 4.6% after the 1 g and 2 g doses. No unwanted local or general reactions were observed. The disappointing clinical results (only 23 out of 36 patients with excellent or good clinical results) one week after the end of the treatment were mainly due to the emergence of pneumococcal infections during (and immediately after) therapy. Considering that Str. pneumoniae is still one of the most important organisms associated with acute purulent exacerbations of chronic bronchitis, and that conventional sputum cultures may not always reveal its presence, there is considerable doubt if aztreonam has any place in the treatment, especially as the results in Ps. aeruginosa infections have also been much poorer than expected.