Phase-transition W/O Microemulsions for Ocular Delivery: Evaluation of Antibacterial Activity in the Treatment of Bacterial Keratitis

Purpose: Moxifloxacin (MXN) is widely prescribed for the treatment of bacterial keratitis. The conventional MXN solution has several limitations, including short precomeal residence time and poor intrastromal bioavailability, requiring frequent instillation of the drug to achieve the desired therapeutic effect. To circumvent this problem, the W/O (water-in-oil) microemulsion (ME) system was utilized for sustained release and improved precomeal retention. Methods: The pseudo-ternary phase diagrams were developed and various MEs were prepared using two nonionic surfactants, Tween 80 and Span 20, with isopropyl myristate and acetate buffer. Physicochemical parameters, in vitro drug release and in vitro antibacterial activity were studied. The in vivo antimicrobial efficacy of optimized microemulsion (ME 10) was studied in an experiment on bacterial keratitis in rabbit eyes and compared with that of the marketed eye drops. Results: The optimized microemulsion (ME 10) displays as an average globule size of <40 nm. The developed MEs showed acceptable physico-chemical behaviour, good stability for 3 months and exhibited sustained drug release. Greater efficacy in experimental bacterial keratitis in rabbit eyes was also observed in comparison with marketed drug solution. Conclusions: The developed MEs are a viable alternative to conventional eye drops, because of its ability to enhance bioavailability through its longer precomeal residence time and its ability to sustain the release of the drug.