Antibiotic effects of WP-0405, a thermo-setting ofloxacin gel, on methicillin-resistant Staphylococcus aureus keratitis in rabbits.

Purpose: The chemotherapeutic effects and pharmacokinetics properties of WP-0405 (a thermo-setting in situ 0.3% ofloxacin-containing ophthalmic gel) and ofloxacin (a conventional 0.3% ofloxacin solution) on methicillin-resistant Staphylococcus aureus (MRSA) keratitis were compared in a rabbit model. Method: The single-instillation pharmacokinetics of WP-0405 and ofloxacin in the cornea, aqueous humor, conjunctiva, and iris-ciliary body were determined in normal rabbit eyes. To compare the duration of antimicrobial action, WP-0405 or ofloxacin was instilled once-daily in an early-treatment model of keratitis, and corneas were either removed immediately or 4 or 8 h postinstillation. In another experiment, WP-0405 was instilled two or three times daily to compare its antibiotic efficacy with three-times daily instillation of ofloxacin in the same early-treatment model of keratitis; corneas were then removed after determining the extent of the abscess area. In another experiment, WP-0405 was instilled four or eight times daily to compare its effects with eight-times daily instillation of ofloxacin in a late-treatment model of keratitis, and corneas were removed. The number of viable bacteria in the corneas was determined in all experiments. Results: C-max and AUC(0-infinity) in tissues treated with WP-0405 were 1.5-3.4-fold and 1.8-2.9-fold greater than those treated with ofloxacin, respectively. WP-0405 significantly reduced the number of viable bacteria for up to 8 h after a single instillation. WP-0405 not only significantly reduced the number of viable bacteria, but also the size of the abscess area at the same frequency of instillation. When compared to ofloxacin, WP-0405 exhibited an approximately equivalent antibiotic effect, with fewer administrations. Conclusions: As a result of its pharmacokinetics, WP-0405 had a more potent, longer-acting antibiotic effect than did ofloxacin. Furthermore, because of its lower required instillation frequency, which would improve patient compliance, WP-0405 has great potential therapeutic benefits.