ID50 of Staph Epidermidis for Keratitis in Rabbits Pre-Treated with Prophylactic Zymar (Gatifloxacin 0.3%)

J Friday and R Snyder, Biomedical Engineering, University of Arizona, Tucson, AZ

Purpose: Refractive surgeons frequently employ a postoperative course of 4th-generation flouroquinolones, Zymar® (gatifloxacin 0.3%) or Vigamox® (moxifloxacin 0.5%), for keratitis prophylaxis after LASIK. This study used a rabbit LASIK model to evaluate the comparative efficacy of a preoperative plus postoperative regimen of gatifioxacin with a postoperative regimen alone.

Methods: Fifty rabbits were divided into two equal groups: control and pretreatment. The test group was pretreated with one drop gatifloxacin QID the day preceding surgery and received one more drop before the procedure. All rabbits received one drop of gatifloxacin post-op and one drop QID for seven days. Following systemic and topical anesthesia, a corneal pocket 3.0 x 3.0 mm was dissected at ~120 um depth in the right eye and inoculated with 2uL of a balanced saline containing concentrations of 10⁴,10⁵, 10⁶, and 10⁷ cfu's of Staph epidermidis.

Results: The ID50 in the control group (post-op drug only) was found to be 10⁵ while the test group was 10⁷. The pretreated group was more resistant to infection, requiring a 100x greater numbers of bacteria to become infected.

Conclusion: In view of these results, LASIK surgeons may be able to reduce the risk of bacterial keratitis by implementing gatifloxacin prophylaxis the day before surgery in addition to a one-week postoperative regimen.

Study supported by an unrestricted grant from Allergan, Inc., RPB and NIH Grant # NIHT35 HL07479

Disclosure code: FCR

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