Topical antibacterial therapy for mycobacterial keratitis: Potential for surgical prophylaxis and treatment

Background: Mycobacterium chelonae and Mycobacterium fortuitum are the 2 most commonly implicated species of nontuberculous myoobacteria in cases of bacterial keratitis. Objectives: This article summarizes available data on the in vitro antibacterial activity against M chelonae or M fortuitum of 2 agents—amikacin and clarithromycin—that have been used in the treatment of bacterial keratitis. In addition, the article reviews the in vitro activity of 5 commercially available topical ocular fluoro-quinolones (in order of availability, ciprofloxacin, ofloxacin, levofloxacin, gatifloxacin, and moxifloxacin) that may have potential in the surgical prophylaxis and treatment of keratitis caused by M chelonae or M fortuitum. Methods: A search of the English-language literature indexed on the MEDLINE, Life Sciences, EMBASE, BIOSIS, and Pharmaprojects databases from 1966 to October 7, 2003, was conducted using the terms Mycobacterium chelonae, Mycobacterium fortuitum, bacterial keratitis, topical antibiotic therapy, ocular infection-mycobacteria, and LASIK infections. Data on the minimum concentrations at which 90% of isolates were inhibited (MIC 90s) were reviewed and compared. Results: In the literature reviewed, the MIC 90 against M fortuitum was from 1 to 16 μg/mL for amikacin, from ≤2 to ≥8 μg/mL for clarithromycin, from 0.1 to 1 μg/mL for ciprofloxacin, from 0.5 to 3.13 μg/mL for ofloxacin, and ≤2 μg/mL for levofloxacin. The results were similar against M chelonae. The fourth-generation fluoroquinolones—gatifloxacin and moxifloxacin—had similar MIC 90s against M fortuitum (both, 0.2 to 1 μg/mL); however, moxifloxacin had greater activity than gatifloxacin against M chelonae (minimum inhibitory concentration range: moxifloxacin, ≤1 to 1.6 μg/mL; gatifloxacin, 3.2 to 6.25 μg/mL). Conclusions: Topical fluoroquinolones may be beneficial for ocular surgical prophylaxis and for the treatment of keratitis caused by M chelonae or M fortuitum. Based on their reported MIC 90s, none of the antibacterials reviewed had greater in vitro activity than moxifloxacin. In addition, moxifloxacin had greater in vitro activity than gatifloxacin against M chelonae, one of the predominant nontuberculous mycobacterial species involved in bacterial keratitis. Pending the conduct of controlled clinical studies, these findings suggest that moxifloxacin may have utility in the prevention and treatment of atypical mycobacterial keratitis.