Delafloxacin-Loaded Poly(<scp>d</scp>,<scp>l</scp>-lactide-<i>co</i>-glycolide) Nanoparticles for Topical Ocular Use: <i>In Vitro</i> Characterization and Antimicrobial Activity

<b>Objective</b>: We developed delafloxacin (Dela)-loaded PLGA nanoparticles (PNPs) for potential ocular application <i>via</i> a topical route to treat eye infections caused by Gram-positive and Gram-negative bacteria. <b>Methodology</b>: Dela-PNPs were formulated using the emulsification-solvent evaporation method and stabilized using poly(vinyl alcohol) (PVA). Size and morphology were characterized by using dynamic light scattering (DLS) and scanning electron microscopy (SEM). Drug loading and encapsulation efficiency were measured <i>via</i> HPLC. Differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR) assessed the physical state and drug-polymer interaction. The <i>in vitro</i> drug release was evaluated using the dialysis bag method in simulated tear fluid (STF, pH 7.4) with Tween 80 (0.5%). The antimicrobial efficacy was determined by a minimum inhibitory concentration (MIC) and zone of inhibition tests against various bacteria. <b>Results</b>: Optimally sized PNPs were produced (238.9 ± 10.2 nm) with a PDI of 0.258 ± 0.084 and a ζ-potential of 2.78 ± 0.34 mV. Using 40 mg of PLGA, 4 mg of Dela, and 1% PVA, drug encapsulation and loading were 84.6 ± 7.3 and 12.9 ± 1.7%, respectively. DSC indicated that Dela was entrapped in an amorphous state within the PNPs. FTIR spectra showed no drug-polymer interactions. The formulation showed 40.6 ± 4.2% drug release within 24 h and 84.4 ± 6.1% by 96 h. MIC tests showed high susceptibility of <i>Streptococcus pneumoniae</i>, <i>Klebsiella pneumoniae</i>, and <i>Escherichia coli</i> (∼0.31 μg/mL) compared to <i>Staphylococcus aureus</i> and MRSA-6538 (∼0.63 μg/mL) and <i>Bacillus subtilis</i> (2.5 μg/mL). Stability studies showed minimal changes in particle characteristics over 3- and 6-month storage at 25 and 37 °C. <b>Conclusion</b>: Dela-PNPs exhibit significant potential as a nanoformulation for ocular applications.