North American (United States and Canada) comparative susceptibility of two fluoroquinolones: ofloxacin and ciprofloxacin. A 53-medical-center sample of spectra of activity. North American Ofloxacin Study Group.

Ofloxacin, a newer broad-spectrum fluoroquinolone, was evaluated against > 12,000 clinical isolates in a multicenter surveillance trial in the United States and Canada using the standardized disk diffusion method. A total of 53 geographically diverse clinical microbiology laboratories contributed zone diameter results for ofloxacin, ciprofloxacin, and norfloxacin for urinary tract infection (UTI) isolates; and ofloxacin and ciprofloxacin for respiratory tract infection (RTI) isolates, skin and soft tissue infection (SSTI) isolates, and genital tract pathogen isolates. In both the USA and Canada, ofloxacin was shown to have the wide spectrum of activity as follows: RTI isolates, ofloxacin (92.2%-93.8% susceptible) > ciprofloxacin (89.5%-90.4%); SSTI isolates, ofloxacin (87.1%-93.6%) > ciprofloxacin (78.8%-90.4%); UTI isolates, ofloxacin (91.6%-92.5%) > norfloxacin (87.3%-91.7%) > ciprofloxacin (86.4%-89.7%); and genital tract isolates, ofloxacin (94.0%) > ciprofloxacin (85.4%) (Canada only). US strains resistant to ofloxacin were confirmed by reference laboratory tests. Confirmed ofloxacin resistance, other than among staphylococci or nonenteric bacilli, was rare. The species most often found to be resistant to both ofloxacin and ciprofloxacin were methicillin-resistant staphylococci, Acinetobacter spp., and Enterococcus spp. From these contributing US and Canadian laboratory studies, ofloxacin appears to have a balanced spectrum of potential clinical use (91.8% susceptible aerobic isolates), particularly against Gram-positive pathogens and some species resistant to ciprofloxacin. The combined overall isolate (12,241 isolates) rates of susceptibility for ciprofloxacin (four infection sites) and norfloxacin (UTI only) were 87.3% and 88.8%, respectively. Monitoring for increasing fluoroquinolone resistance should be considered, however, as greater use of drugs in this class develops.