(M1430-12-79) Gatifloxacin Nanoemulsions Prepared by Hot Melt Extrusion/Hot-Homogenization for Bacterial Conjunctivitis.

Purpose: Bacterial conjunctivitis, one of the most common infections of the eye, can cause complications such as keratitis, corneal ulceration, perforation, and blindness if left unaddressed. Gatifloxacin (GTX) is a fourth-generation fluoroquinolone, active against both gram-negative and positive bacteria, and is approved as an ophthalmic solution (0.5% w/v) for bacterial conjunctivitis. Low precorneal retention and high tear drainage lead to a lower bioavailability for drugs in ophthalmic solutions. Thus, this work is aimed at developing stable GTX nanoemulsions (NE) to improve the ocular surface retention and bioavailability of the drug. Two technologies were evaluated for the preparation of the NE, Hot Melt Extrusion (HME)-Probe Sonication and Hot-Homogenization-Probe Sonication.

Methods: The lipid solubility of GTX was visually screened in selected liquid lipids at 60° C by stirring at 2000rpm for 10 min, then cooled and stored at room temperature for 24 hours. The partition behavior of GTX between the lead liquid lipid and the aqueous phase was studied. The saturation solubility of GTX was studied in the lead liquid lipid to determine the maximum drug load. GTX (0.5% w/v) nanoemulsions consisted of the drug dissolved in the lead liquid lipid and an aqueous phase consisting of Tween® 80 (surfactant), Poloxamer 407 (cosurfactant), TPGS (permeation enhancer), Glycerin (tonicity adjustor), and Milli-Q water. The NEs were prepared using hot homogenization-probe sonication (GTX-NE) or HME-probe sonication (GTX-HME-NE) methods. The lead NEs were evaluated for their viscosity, in vitro release/diffusion, transcorneal permeation, antimicrobial efficacy, effect of sterilization, and stability over 3 months (at 4°, 25°, and 40° C) for pH, droplet size (DS), polydispersity index (PDI), zeta potential (ZP), and drug content.

Results: GTX showed a saturation solubility of 155 ± 0.3 mg/mL in oleic acid (lead lipid from the visual solubility study). The partition coefficient of GTX between oleic acid-water and oleic acid-aqueous phase systems was 50.5 and 16.9, respectively, indicating the higher affinity of GTX for the lipid phase of the NEs. GTX-NE and GTX-HME-NE showed similar DS (173 to 179 nm), PDI (0.16 to 0.17), ZP (-39 to -36 mV), viscosity (18 to 21 cP), pH (5.8 to 5.9), and drug contents (99 to 100%). GTX-NE and GTX-HME were sterilized by filtration and autoclaving. There were no significant (p < 0.05) changes to the formulation characteristics before and after sterilization. GTX-NE and GTX-HME-NE showed a sustained release of GTX over 24 hours (T_50% = 3 hours) while the control solution showed 100% release within 1.5 hours. Transcorneal flux and permeation across rabbit cornea for both nanoemulsions were observed to be 2.5- and 3-fold higher, respectively, over the control solution. Both GTX-NE and GTX-HME-NE showed a minimal inhibitory concentration (MIC₉₀) of 6.25 µg/mL against methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas aeruginosa (PA), which was comparable to that of the control solution (6.25 µg/mL). Moreover, the NE formulations were stable over a three-month testing period with respect to their physicochemical properties at 4°, 25°, and 40° C (p < 0.05).

Conclusion: Stable nanoemulsions of GTX were successfully prepared using hot homogenization-probe sonication and HME-probe sonication and sterilized using filtration/autoclaving. GTX nanoemulsions could be investigated for application in treating bacterial conjunctivitis and HME could be potentially developed as a continuous manufacturing process for GTX nanoemulsions.

Figure 4. In vitro drug release profile of GTX from GTX-NE, GTX-HME-NE, and commercial solution (control) in relation to the determined MIC90 (mean ± SD, n=3) (p < 0.05)

Figure 5. Transcorneal flux, and permeability of Gatifloxacin from GTX-NE, GTX-HME[1]NE, and Control formulations across isolated rabbit cornea (mean ± SD, n=4) (p < 0.05)