Selective decontamination of the digestive tract with aztreonam: a study of 10 healthy volunteers.

Aztreonam, a minimally absorbable monobactam antibiotic that is active primarily against gram-negative bacilli, was given orally to 10 healthy volunteers in three regimens: 60 mg, 300 mg, and 1,500 mg daily for five days. The regimens were administered at least two weeks apart so that the flora could return to normal. Aztreonam had no effect on oropharyngeal flora cultured every other day. Fecal cultures from volunteers receiving the 300-mg regimen yielded no gram-negative bacilli after an average of 4.4 days of treatment. Administration of the highest dose gave similar results, albeit after a shorter interval (3.0 days). None of the regimens appreciably influenced total microscopic (anaerobic) bacterial counts in the feces. However, during administration of the 1,500-mg regimen, fecal counts of enterococci increased from an average of approximately 10(4)/g to greater than 10(7)/g, and fecal counts of yeasts tended to increase by the end of the five-day treatment period. Fecal concentrations of aztreonam increased as the dose increased in eight volunteers. No aztreonam was recovered from the feces of two volunteers, perhaps because of drug inactivation.