Does In Vitro Susceptibility Predict Clinical Outcome in Bacterial Keratitis?

Purpose: To determine whether clinical outcomes in bacterial keratitis are associated with antibiotic susceptibility. Design: Retrospective, ancillary study using data and samples from a completed randomized clinical trial. Methods: Forty-two patients were enrolled with culture-confirmed bacterial keratitis at Aravind Eye Hospital in South India. All patients received topical moxifloxacin and were randomized to receive either topical prednisolone phosphate or placebo. Outcomes included time to epithelialization, best spectacle-corrected visual acuity (BSCVA), and infiltrate/scar size at three months. Bacterial isolates were cultured, and minimum inhibitory concentration (MIC) to moxifloxacin was measured using Etests. Multiple linear regression was used to assess the effect of MIC on outcome, adjusting for enrollment characteristics. Results: MIC was associated with three-month infiltrate/scar size: each two-fold increase in MIC was associated with a 0.33-mm average diameter increase in scar size (P = .01). MIC was not associated with three-month BSCVA (P = .71) or time to epithelialization (P = .35). Conclusions: MIC was associated with infiltrate/scar size in bacterial keratitis. An ongoing larger, multicenter trial should provide further information on whether this association is maintained across subgroups of organisms.