Quinolone resistance. Susceptibility data from a 300-bed community hospital.

Introduction of the fluoroquinolones has altered physician prescribing practices in the treatment of infectious diseases for both inpatients and outpatients. To evaluate the impact of unrestricted prescribing of these agents, the antimicrobial susceptibility of clinical isolates to ciprofloxacin and other commonly used antibiotics was prospectively studied in a 300-bed community teaching hospital. Only 0.6 percent (nine of 1,454 isolates) of fresh clinical isolates were resistant to ciprofloxacin (minimal inhibitory concentration value greater than 2 micrograms/ml) in an initial study conducted between 1984 and 1985. A similar pattern was observed in the second half of 1987 (0.5 percent, or five of 940 isolates), just prior to the release of ciprofloxacin. Throughout 1988, however, as quinolone usage rose, the incidence of ciprofloxacin resistance rose, reaching a peak of 4.0 percent in the last quarter of 1988. Of 63 ciprofloxacin-resistant isolates in 1988, 22 were Pseudomonas and 28 were staphylococci, representing resistance rates of 6.5 and 4.2 percent, respectively. Enterobacteriaceae remained exquisitely susceptible with only five of 1,720 isolates (0.3 percent) resistant to ciprofloxacin. Seventy-two percent of ciprofloxacin-resistant isolates were recovered from patients who had received a fluoroquinolone within the previous month. If these isolates are subtracted from the total number of resistant micro-organisms recovered, baseline fluoroquinolone resistance did not change significantly from 1984 to 1988. Soft-tissue infections (50 percent) represented the greatest source of ciprofloxacin-resistant organisms, including osteomyelitis, but urinary tract infections (26 percent), all associated with instrumentation, were also a significant source. Although the fluoroquinolones are extremely valuable antimicrobial agents, the emergence of drug resistance may be promoted when these drugs are used for treatment of chronic infections or when poorly drained abscesses, necrotic tissue, or indwelling foreign bodies are present.