1st October 2010
Bacterial Keratitis: Is Monotherapy Adequate?
I'll never forget a patient I treated in Ghana, West Africa. She was a fish seller, someone who bought fish from local fishermen, cut them up and sold them on the streets. One day while chopping off fins to prepare her wares for market, a spine ricocheted into her eye. Within a few hours, the pain had worsened significantly. When I saw her in my clinic, there was a 2 mm corneal infiltrate.
I was accustomed to treating corneal ulcers with a fluoroquinolone plus fortified topical gentimicin. But, because she was poor, and because the ulcer was small, I deviated from my usual practice and treated her with ciprofloxacin eye drops alone-every 5 minutes for 30 minutes, then every 30 minutes for the rest of the night.
The next morning I was aghast at what I saw! The entire cornea was infected-from limbus to limbus. The cause? Strep, I knew it! The problem of Strep being resistant to fluoroquinolone antibiotics is something I had done research on1. What shocked me was how such a small ulcer could progress so rapidly in spite of aggressive topical fluoroquinolone treatment.
This problem was recently highlighted in the journal Investigative Ophthalmology & Visual Science2. The authors found a fairly high rate of failure (9%) using monotherapy for bacterial keratitis with either ciprofloxacin or ofloxacin, particularly due to resistance from Strep pneumonia and other Streptococcus species.
What I found particularly interesting is that this study failed to show a correlation between MIC values for fluoroquinolones and clinical response in Strep keratitis. This is important because newer fluoroquinolones (e.g. moxifloxacin and gatifloxacin) claim improved efficacy in the gram-positive spectrum based solely upon in vitro results. The study results suggest that these newer antibiotics, despite their claims, may not offer improved in vivo results against Strep species. Experimental animal research will be needed to determine whether these new antibiotics really are effective versus infectious corneal ulcers from Strep.
I advise caution 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). My research has shown this to be the best treatment.
- Guzek JP, Cline DJ, et al. Rabbit Streptococcus pneumoniae keratitis model and topical therapy, Investigative Ophthalmology & Visual Science 1998; 39(11):2012-7
- Kaye S, Tuft S, Tole D, et al. Bacterial Susceptibility to Topical Antimicrobials and Clinical Outcome in Bacterial Keratitis, Investigative Ophthalmology & Visual Science 2010; 5(1) 62-368