In vitro activity of S-ofloxacin.

S-Ofloxacin, the optically active form of ofloxacin, was twice as active as the S,R mixture of ofloxacin against members of the family Enterobacteriaceae, Pseudomonas aeruginosa, and gram-positive species. Of the Enterobacteriaceae, 90% were inhibited by less than or equal to 1 microgram/ml and 90% of Staphylococcus aureus and Streptococcus pyogenes isolates were inhibited by 0.5 microgram/ml. Bacteroides fragilis was inhibited by 4 micrograms/ml. Organisms resistant to ofloxacin were resistant to S-ofloxacin. Like ofloxacin activity, the activity of S-ofloxacin was reduced by Mg2+ and by acid pH. Spontaneous mutational resistance to S-ofloxacin was similar to that to ofloxacin.