International Journal of Applied Pharmaceutics ISSN - 0975 - 7058 Vol 11, Special Issue 5, 2019 ABSTRACT Objective: This study aimed to optimize and evaluate the controlled release rate, ocular irritancy, and in vitro antimicrobial properties of levofloxacin entrapped in the epichlorohydrin-crosslinked hydrogel of sodium carboxymethyl cellulose (NaCMC) and gelatin. Materials and Methods: Various parameters such as polymer ratio, amount of crosslinker, temperature, reaction time, swelling capacity, and percent drug loading were considered in Optimized levofloxacin hydrogel. Hydrogel preparations with higher amount of drug loaded were further analyzed to determine its in vitro drug release rate, ocular irritancy on New Zealand rabbits, and antimicrobial activities against Pseudomonas aeruginosa and Staphylococcus aureus. Optimized levofloxacin hydrogel (OLH) was then subjected to 3-month stability testing at 40 ± 2°C and 75 ± 5% relative humidity in which samples were withdrawn at the end of each month for analysis. Results: Polymer groups with higher concentrations of NaCMC have higher swelling and drug loading capacities than those with higher gelatin concentrations. Meanwhile, qualitative analysis using differential scanning calorimetry, Fourier-transform infrared spectroscopy, and scanning electron microscopy verified the presence of levofloxacin in the epichlorohydrin-cross-linked hydrogel. Among the four polymer ratio, F3 was the optimized hydrogel with drug-loaded concentration of 99.50%, which was within the acceptable assay limit of 0.5% levofloxacin solution based on United States Pharmacopeia monograph. It followed the Higuchi kinetic model with a drug release mechanism of super case 2 transport indicating hydrogel swelling as a key factor for its controlled drug release. In vitro, antibacterial test against P. aeruginosa and S. aureus was sensitive to optimized levofloxacin hydrogel (OLH) with inhibitory diameter zones of 31.68 and 37.05 mm, respectively. Ocular irritancy test also showed that the OLH is non-irritating on installation in the cul-de-sac of New Zealand rabbits. Conclusion: Optimized levofloxacin hydrogel was effective, non-irritating, and stable, which can be used as an alternative to conventional 0.5% levofloxacin ophthalmic solution. Keywords: Cross-linked hydrogel, Levofloxacin, Ophthalmic preparation. INTRODUCTION Misuse and overuse of antimicrobials impair their abilities to treat infections. It can also prolong illnesses which may lead to disabilities and deaths. Eye infections such as bacterial and fungal keratitis are one of the major causes of ophthalmic morbidities and visual loss with a reported incidence of 17–36% worldwide [1]. It is also a second predisposing factor of corneal opacifications which is commonly associated with soft contact lens users with a reported annual ulcerative keratitis incidence of 4–21/10,000 daily and extended wear users [2]. In this case, clinicians use varieties of antibacterial eye preparations and reports have shown that ocular pathogens show minimal bacterial resistance with fluoroquinolones [3] such as 0.3% ciprofloxacin and 0.5% levofloxacin which are efficient against aminoglycoside-resistant Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus. Levofloxacin, a fourth-generation fluoroquinolone and an active L-isomer of Ofloxacin, is proven safe in treating bacterial conjunctivitis, keratitis, and other eye infections with known mechanism of inhibiting DNA gyrase and topoisomerase IV which are important steps for bacterial DNA metabolism [4]. It is registered as Quixin ® (US), Oftaquix ® (Europe), and Cravit ® (Japan) with disadvantages similar to conventional eye preparations, such as rapid tear turnover and drug impermeability to corneal epithelium membranes similar to other conventional eye drops. Patient non-compliance is also an issue due to high frequencies of eye drop installations, which is a contributory factor to microbial resistance aside from improper dosage regimen, misuse, and overuse of topical antibacterial and extended duration of therapy. In situ, hydrogel is a polymer liquid solution that undergoes a phase transition to semisolid gel due to changes in pH, temperature, and ion activation. On addition of a crosslinker specifically epichlorohydrin, its mechanical strength, and swelling properties will be enhanced, allowing diffusion of water-soluble drug into the hydrogel [5]. The main thrust of this study was to enhance the permeability and release rate of levofloxacin through drug entrapment in an epichlorohydrin- cross-linked hydrogel consisting of sodium carboxymethylcellulose (NaCMC) and gelatin. MATERIALS AND METHODS Materials Epichlorohydrin and the reference standard levofloxacin were purchased from Sigma-Aldrich, while the high-performance liquid chromatography grade methanol for OLH analysis was purchased from Merck. Other analytical grade chemicals were acquired from Aishite Trading. Methods Compatibility testing Thermograms of individual and combined ingredients were obtained using PerkinElmer differential scanning calorimetry (DSC) 400 in which Research Article IN VITRO ENTRAPMENT AND RELEASE STUDIES OF LEVOFLOXACIN USING EPICHLOROHYDRIN-CROSSLINKED HYDROGEL ANGELI ANN S. RESCOBER 1,2* 1 College of Pharmacy, Adamson University, Manila, Philippines. 2 Graduate School, Centro Escolar University, Manila, Philippines. Email: aasrescober@ymail.com Received: 19 July 2019, Revised and Accepted: 20 July 2019 © 2019 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open access article under the CC BY license (http://creativecommons. org/licenses/by/4. 0/) DOI: http://dx.doi.org/10.22159/ijap.2019.v11s5.T0107 4 th International Conference on Pharmacy and Pharmaceutical Science (ICPPS) 2019