Treatment of atypical pneumonia with azithromycin: comparison of a 5-day and a 3-day course.

The efficacy of a 5-day regimen consisting of 500 mg in a single dose on the first day followed by 250 mg once daily for 4 consecutive days was compared with that of a 3-day course of azithromycin given in single daily doses of 500 mg for treatment of atypical pneumonia. Adult patients hospitalized with atypical pneumonia in the years 1990 to 1993 were studied retrospectively. For each patient, the medical history, laboratory data, the results of serological tests, chest radiographs and treatment outcome were reviewed. Out of 148 patients with atypical pneumonia, 40 were treated with azithromycin for 5 days (Group 1) and 41 for 3 days (Group 2). The success rate in Group 1 was 80% (32 patients). Eight patients did not respond to treatment: 5 had significant complement fixing antibody titers to adenovirus and in 3 the etiology was unknown. The success rate in Group 2 was 88% (36 patients). Azithromycin was ineffective in all 3 patients with adenoviral pneumonia, in 1 patient with Q fever, and in 1 patient with no identified pathogen. Azithromycin is equally effective as treatment of atypical pneumonia in adult patients if given for 3 or 5 days at the same total dose.