Augmented efficiency of azithromycin for MRSA ocular infections management: Limonene-based nanostructured lipid carriers in-situ approach

Staphylococcus aureus (S. aureus) is the main pathogen that leads to serious ocular infectious disorders such as endophthalmitis and keratitis. A major obstacle in managing such infections is antibiotic resistance, as illustrated by the development of methicillin-resistance S. aureus (MRSA) strains. D-limonene, a main constituent of the citrus peel oil, is known for its potential antibacterial effect, thus, the objective of the current study is to fabricate a safe and effective in-situ ocular limonene-based nanostructured lipid carriers (NLCs) gel to improve azithromycin (AZ) solubility and efficacy against methicillin-susceptible S. aureus (MSSA) and MRSA-associated ocular biofilm infections. NLCs consisting of limonene and Gelucire & REG; as an oily phase and Labrasol & REG; and Labrafil & REG; as an aqueous phase were prepared by cold microemulsion technique and characterized regarding their physicochemical characterizations. Besides, in-vitro antimicrobial sensitivity has been assessed on biofilmforming MSSA and MRSA strains via killing kinetics and biofilm examination. NLCs-based in-situ gel was developed using Pluronic & REG; F 127 and hydroxypropyl methylcellulose (HPMC) and evaluated regarding its physicochemical properties, in-vitro release, ex-vivo trans-corneal permeation through ocular sheep, and its ocular safety profile utilizing HET-CAM test. NLCs displayed a nanometric size of 77.42 & PLUSMN; 0.82 nm, narrow size distribution (0.196 & PLUSMN; 0.006), and spherical shape with ameliorated MRSA biofilm eradicating efficacy, in which MIC and MBC of AZ-loaded NLCs were 4 & mu;g/ml and 64 & mu;g/ml, respectively, significantly less than that of free AZ which were 16 & mu;g/ml and 128 & mu;g/ml, respectively. NLCs-based in-situ gel illustrated 1.25-fold enhancement in ex-vivo trans-corneal permeability with a steady-state flux of value 3.01 & PLUSMN; 0.2 & mu;g/cm2.min compared to the control in-situ gel (2.41 & PLUSMN; 0.8 & mu;g/cm2.min) with a safe ocular profile revealing zero irritation index compared with 9.87 for the positive control group. Accordingly, NLCs-based in situ-gel is a promising vehicle against resistant bacterial strains with superior safety and efficacy.