PROJECT SUMMARY About 70% of all ocular infections are caused by bacteria. Each year in the US alone, there are millions of cases of bacterial keratitis and conjunctivitis. Fluoroquinolones are effective for both treatment and prevention of these infections, and moxifloxacin is often the drug of choice due to higher intraocular bioavailability compared to other fluoroquinolones. The newest fluoroquinolone, besifloxacin, has also shown to have some advantages in treating resistant organisms, including methicillin-resistant Staphyloccocus species and Pseudomonas species associated with contact lens-related keratitis. Regardless, antibiotic eye drops are prescribed to be used at least three times per day, and up to once every hour for severe infections. As the required number of doses per day increases, patient compliance, and thus, treatment efficacy, decreases. Issues with adherence can lead to sight-threatening complications and potentially contribute to bacterial resistance. Antibiotic eye drop formulations that are more effective with less frequent dosing are needed to improve patient outcomes and quality of life and slow the development of bacterial resistance. While eye drops dominate the ophthalmic market, achieving effective intraocular drug delivery via eye drops is quite challenging. Tear production, reflexive blinking, and nasolacrimal drainage limit residence time, while formulation and drug properties can further limit the potential for the rapid intraocular drug absorption needed. We have developed a mucosal drug delivery technology that increases drug delivery and absorption across mucosal barriers, termed the mucus-penetrating particle (MPP) technology. Here, we describe an innovative approach for formulating water-soluble fluoroquinolone antibiotic salts into ion-paired drug-core nanosuspensions. Our preliminary data demonstrates that a moxifloxacin-pamoic acid MPP nanosuspension (MOX-PAM NS) provides improved prevention and treatment in a rat model of bacterial keratitis. Importantly, once daily dosing with MOX-PAM NS was as good or better than three times daily dosing with the commercial formulation, Vigamox. The goal is to develop eye drop formulations of both moxifloxacin and besifloxacin to provide broad spectrum treatment options for gram-positive, gram-negative, and resistant bacterial infections. In Aim 1, we will make further formulation changes in the eye drops to increase intraocular drug absorption and screen for antimicrobial activity against commercial and clinical bacterial isolates. In Aim 2, we will characterize the topical drug penetration and efficacy in treating bacterial keratitis in rats. In Aim 3, we will perform full pharmacokinetic studies, treatment efficacy studies, and topical safety studies in rabbits, which have ocular size and structure more similar to humans. We anticipate that a reduction in dosing frequency while maintaining efficacy against a wide range of common bacterial pathogens will have a po...