Comparison of the in vitro activity of ofloxacin and gentamicin against isolates from hospitalised patients.

The in vitro activity of ofloxacin (Hoe 280) against Staphylococcus aureus, some Enterobacteriaceae and Pseudomonas spp. is compared with that of gentamicin using the agar dilution method to determine the minimal inhibitory concentration of each agent for the isolates. Ofloxacin and gentamicin were found to have similar activity against Staphylococcus aureus with an MIC50 of 0.25 mg/l and an MIC90 of 1.0 mg/l. However, ofloxacin appears to be more active against the Enterobacteriaceae than gentamicin with lower MICs for some species of that family. Ofloxacin was found to have an MIC50 value of 0.25 mg/l for the Enterobacteriaceae and an MIC90 of 1.0 mg/l while the MIC90 of gentamicin for the same isolates was 32.0 mg/l. A significant proportion of our Pseudomonas spp. were resistant to gentamicin with an MIC90 of over 16 mg/l and a range of 0.5 mg/l to greater than 128 mg/l. Ofloxacin had an MIC range of 0.25 to 4.0 mg/l for the same organisms.