Problems with Monotherapy for Bacterial Keratitis

I read with interest the article by Kaye et al. ¹ in the January issue, “Bacterial Susceptibility to Topical Antimicrobials and Clinical Outcome in Bacterial Keratitis.” The authors found a fairly high rate of failure of monotherapy for bacterial keratitis with either ciprofloxacin or ofloxacin (9%), particularly due to resistance from Streptococcus pneumoniae and other Streptococcus species. Based on my October 1998 publication in the journal, ² I was not surprised. What did surprise me is that the authors did not add topical fortified gentamicin when faced with a clinical failure due to Streptococcus sp. My experimental data and my anecdotal clinical experience suggest that this treatment would have been beneficial. 

The authors are to be commended, however, for showing the lack of correlation between the MICs (minimum inhibitory concentrations) of fluoroquinolones and the clinical response of streptococcal keratitis. This finding is important because the newer fluoroquinolones (e.g., moxifloxacin, gatifloxacin) have been said to have improved efficacy in the Gram-positive spectrum, solely on the basis of in vitro results. The results of Kaye et al. suggest that these newer antibiotics, despite the claims, may not offer improved in vivo results against Streptococcus species. Because of this possibility, caution seems advisable when using monotherapy for any serious bacterial corneal ulcer. Instead, I prefer a topical fluoroquinolone (whichever agent) plus topical fortified gentamicin (13.6 mg/mL).