Influence of fluoroquinolone susceptibility on the therapeutic response of fluoroquinolone-treated bacterial keratitis.

OBJECTIVE To estimate how a corneal isolate's minimal inhibitory concentration for a fluoroquinolone agent affects the rate of clinical response of bacterial keratitis to fluoroquinolone therapy. DESIGN Prospective cohort study. METHODS Six hundred sixty-three individuals with suspected bacterial keratitis underwent diagnostic corneal scraping and were treated with topical 0.3% ciprofloxacin solution or ointment. Of 407 patients with culture-confirmed bacterial keratitis, improvement and cure rates with ciprofloxacin monotherapy were estimated for 391 who had in vitro ciprofloxacin susceptibility of the principal corneal isolate. MAIN OUTCOME MEASURES Slitlamp biomicroscopic assessment for clinical improvement of corneal inflammation and for clinical cure with complete reepithelialization. RESULTS Adjusted rates of improvement and of cure were reduced, respectively, by 43% (95% confidence limits, 8%, 64%) and by 29% (95% confidence limits, 0%, 49%) among corneal infections having a ciprofloxacin minimal inhibitory concentration above 1.0 micro g/mL compared with those with more sensitive isolates. CONCLUSIONS Corneal infection by relatively ciprofloxacin-resistant bacteria responds more slowly to ciprofloxacin therapy. Antibacterial susceptibility testing of corneal cultures may predict the fluoroquinolone therapeutic response rate of bacterial keratitis.