The in situ drug delivery system and colloidal formulation like micro emulsion has potential to use in ocular delivery. Micro emulsion provides better permeation of drug through the membrane and provides improved bioavailability. The in situ drug delivery system decreases pre-corneal drainage, increase the contact time of formulation with eye and prolong the release in ocular tissues. Again, in situ gelling system has advantage of delivering accurate and reproducible quantities each time, against any already gelled formulations. To combine the benefits of these two dosage forms, micro emulsion based in situ gelling system can be developed as a novel vehicle for ophthalmic drug delivery. Endophthalmitis is an infection of intraocular fluids like vitreous humor and ocular tissues. To combat the disease, the formulation which provides sufficient concentration in posterior segment eye diseases (PSED) is required. Keywords: Posterior segment eye diseases, micro emulsion, drug delivery system, ocular, formulation.

Objectives: The purpose of this research was to develop the micro emulsion-based in situ gelling systems containing Ciprofloxacin for prophylaxis and treatment of the posterior segment diseases like endophthalmitis. Methods: Ciprofloxacin was encapsulated in small droplets owing to form microemulsion, and then the formed droplets were dispersed in a polymer solution that converted into a gel upon triggered by the electrolyte present in the tear fluid. Results: The formulation approach provides better absorption, penetration, retention, and improves the bioavailability of the drug. The average concentration reached into vitreous humor from topical microemulsion in situ gelling formulation was ~0.4 µg/ml, which is far more than the concentration required for therapeutic effect (i.e.  >0.047 µg/ml or >MIC90 for S. Epidermidis, a pathogen commonly responsible to cause endophthalmitis). Conclusion: Thus, novel micro emulsion-based in situ gelling formulation could be a potential drug delivery system for the treatment of posterior segment diseases like endophthalmitis. Keywords: Microemulsion, ciprofloxacin, endophthalmitis, ocular, infection, in situ