Meeting Highlights: 44th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC)

A single dose of a novel formulation of azithromycin microspheres (Pfizer) has proved to be as effective as a seven-day course of levofloxacin (Levaquin®, Ortho-McNeil) for the treatment of an acute exacerbation of chronic bronchitis (AECB). This advance has made it possible to administer an entire regimen as a single oral dose while maintaining tolerability and efficacy. In a multicenter, randomized, double-blind, double-dummy clinical trial, 551 patients with AECB were randomly assigned to receive azithromycin microspheres as a 2-g single dose or levofloxacin 500 mg once daily for seven days. The primary and secondary endpoints were clinical and bacteriological responses, respectively, in patients with a baseline pathogen at the test-of-cure (TOC) visit between days 14 and 21. A total of 438 patients—220 receiving azithromycin microspheres and 218 receiving levofloxacin—met the criteria for the clinical-per-protocol (CPP) population at the TOC visit. The CPP cure rates were comparable in the two treatment groups: 93.6% for azithromycin microspheres and 92.7% for levofloxacin. The bacteriological-per-protocol (BPP) population consisted of 247 patients: 123 received azithromycin microspheres and 124 received levofloxacin. The overall bacteriological eradication rates at the TOC visit were 91.9% for azithromycin microspheres and 94.4% for levofloxacin. Because many patients were unable to produce sputum at the TOC visit, most of the pathogens were assigned a bacterial response of presumed eradication according to an assessment of the clinical response. The clinical cure rates for patients with Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, isolated at baseline, were similar in the azithromycin patients (95.0%, 94.7%, and 92.0%, respectively) and in the levofloxacin patients (100%, 90.5%, and 81.3%, respectively). Both drugs were well tolerated. Because azithromycin therapy can be administered as a single dose, the rate of compliance was 100% in patients following this regimen. In contrast, 14 of 279 patients in the original levofloxacin group (5%) did not complete the entire seven-day course of active treatment.