Rosamicin: in vitro activity against anaerobes and comparison with erythromycin.

The in vitro activity of rosamicin was determined against 231 strains of anaerobic bacteria and compared with the activity of erythromycin against the same strains. Rosamicin and erythromycin had similar activity against strains of Peptostreptococcus and gram-positive nonsporeforming bacilli. Rosamicin was somewhat more active against strains of Peptococcus, Clostridium, and gram-negative anaerobes. All strains of Bacteroides fragilis tested were inhibited by 4 mug of rosamicin or less per ml, whereas only 76% of them were inhibited by this concentration of erythromycin. Rosamicin was distinctly more active against Fusobacterium nucleatum. Because of its in vitro activity, further investigation of the pharmacology of this drug is warranted.