Efficacy and safety of low-dose aztreonam in the treatment of moderate to severe infections due to gram-negative bacilli.

One hundred fifty-three patients with moderate to severe infections due to gram-negative bacilli, including septicemia (60 cases), lower respiratory tract infection (32 cases), intraabdominal infection (40 cases), and urinary tract infection (21 cases), were treated with aztreonam (1 g every 12 h). This dosage is lower than usual. Criteria for inclusion in the study included documented infection due to gram-negative bacilli and a measurement of severity of disease of less than 12 (as defined by a Simplified Acute Physiology Score for the 115 cases of community-acquired infection). Other than aztreonam, no antibiotic active against gram-negative bacilli was allowed to be used for treatment. Seventy-one patients in whom gram-positive or anaerobic organisms were detected or suspected were given additional agents effective against the organisms. One hundred forty-one patients (92.2%) were cured; the mean duration of treatment was 10.9 +/- 4.0 days. None of the gram-negative bacilli initially isolated became resistant to aztreonam. Colonization, generally by a gram-positive organism, was observed in 27 patients and superinfection was observed in five. Aztreonam was well tolerated. This study suggests that a dosage of 2 g daily of aztreonam should be appropriate in the treatment of moderate to severe infections due to susceptible gram-negative bacilli.