Bacterial Susceptibility to Topical Antimicrobials and Clinical Outcome in Bacterial Keratitis

Abstract

With fluoroquinolone monotherapy, there was significant association between the MIC of the antimicrobial prescribed and the clinical outcome with all bacteria except CNS and Streptococcus spp. The approach used in this study, if used prospectively, could allow topical breakpoint susceptibility concentrations to be determined for individual antimicrobial and bacterial combinations.

Clinical characteristics and outcomes of patients admitted with presumed microbial keratitis to a tertiary medical center in Israel

“…Some authors (22) studied a model to determine the impact of mi nimal inhibitory concentration (MIC) on the clinical outcome. It included patients who received monotherapy with a fluoroquinolone who had no subsequent change in their treatment and whose ulcers healed without surgical intervention.…”

Orlans HO, Hornby SJ, Bowler IC (2011) In vitro antibiotic susceptibility patterns of bacterial keratitis isolates in Oxford, UK: a 10-year review. Eye Jan 21 [Epub ahead of print] PMID 21252952

“…Interestingly, we have found that MICs were only associated with clinical outcome in 14-15% of cases of bacterial keratitis [11]. Therefore, although initiating prompt and appropriate topical antimicrobial therapy is essential to the management bacterial keratitis, it is clear that other factors, for example bacterial virulence factors, affect the clinical outcome.…”

“…Topical administration of an antimicrobial to the eye involves mixing with the tear film, and so, loss of drug from the precorneal area is a net effect of corneal and non-corneal absorption, tear secretion, and drainage. Breakpoint concentrations have not been determined for topical antimicrobials, although there is evidence [9][10][11] demonstrating the relationship between MIC of topically applied antimicrobials and clinical outcome in bacterial keratitis. Previous work from our group has a demonstrated a direct relationship between bacterial susceptibility to a given antimicrobial in terms of MIC and reduction in healing time [11].…”

“…Breakpoint concentrations have not been determined for topical antimicrobials, although there is evidence [9][10][11] demonstrating the relationship between MIC of topically applied antimicrobials and clinical outcome in bacterial keratitis. Previous work from our group has a demonstrated a direct relationship between bacterial susceptibility to a given antimicrobial in terms of MIC and reduction in healing time [11]. We found a significant association between the MIC of a fluoroquinolone and clinical outcome for Pseudomonas spp., S. aureus, and Enterobacteriaceae, but not for Streptococcus spp.…”

“…Combination therapy may offer a broader spectrum of activity [11] and reduce resistance selection pressures when compared to monotherapy; however, combinations of antimicrobials do not always result in synergistic or additive activity, and further studies on combination therapy for bacterial keratitis are required. The introduction of antimicrobials that are used increasingly to treat systemic infection into ophthalmic practice is an opportunity to improve treatment.…”