MAY 03, 2013
This study analyzing the relationship between fluoroquinolone use at presentation and minimum inhibitory concentration (MIC) in bacterial keratitis provides evidence that prior use of fluoroquinolones is associated with antibiotic resistance.
The authors compared antibiotic use at presentation with MIC against moxifloxacin hydrochloride 0.5% in 480 cases from the Steroids for Corneal Ulcers Trial, a randomized, double-masked, placebo-controlled trial with the primary objective of assessing the effect of adjunctive topical corticosteroid treatment on outcomes in bacterial keratitis.
Topical fluoroquinolone use at presentation was reported in 92 of 480 cases, or 19.2 percent. Causative organisms in the 480 cases included Streptococcus pneumonia in 247 cases, Pseudomonas aeruginosa in 109 cases and Nocardia species in 55 cases.
Isolates from patients who reported fluoroquinolone use at presentation had a 2.01-fold higher MIC (P < 0.001). Fourth-generation fluoroquinolones were associated with a 3.48-fold higher MIC than those isolates that were not exposed to pretreatment at enrollment (P < 0.001). Overall, patients with fluoroquinolone use at presentation had a different spectrum of bacterial isolates than patients without fluoroquinolone use at presentation (P < 0.001).
The authors say these results suggest that fluoroquinolone use may select for growth of certain less susceptible species and also selects for resistant strains within a species. They conclude that isolates pretreated with the newer fluoroquinolones appear to be driving the higher MICs, and an increase in topical antibiotic therapy before presentation may contribute to increasing observed resistance.