Development and Evaluation of Azithromycin-Loaded Transethosomes for Enhanced Dermal Delivery and Antibacterial...

Background/Objectives: The topical delivery of antibiotics through transethosomes shows promise for enhancing its dermal delivery for the treatment of skin infections. This study aimed to develop and characterize azithromycin-loaded transethosomes to enhance topical drug delivery and improve the antibacterial activity of azithromycin. Methods: The prepared azithromycin formulations underwent assessment for various characteristics, including their vesicle dimensions, size distribution, zeta potential, encapsulation efficiency, and morphological features (via TEM analysis). Additionally, their thermal properties were examined through DSC analysis, and their stability was monitored over six months under refrigerated storage conditions. The sequential tape-stripping technique was employed to conduct ex vivo penetration studies on human skin. Interactions between transethosomes and stratum corneum lipids were examined using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). Additionally, the formulations were tested for their in vitro antibacterial efficacy against Staphylococcus aureus. Results: The findings revealed that AZ 1 and AZ 2 had vesicle sizes of 108.44 ± 5.72 nm and 70.42 ± 6.02 nm, zeta potential measurements of -11.897 ± 1.820 mV and -34.575 ± 4.535 mV, and high entrapment efficiencies of 99.259 ± 0.086% and 99.560 ± 0.014%, respectively. Transmission electron microscopy (TEM) analysis confirmed the spherical nature of the vesicles, whereas differential scanning calorimetry (DSC) confirmed the successful encapsulation of azithromycin in transethosomes. The formulations exhibited acceptable physical stability at 4 °C for six months. Ex vivo studies revealed a significantly higher deposition of azithromycin in the skin by both transethosome formulations than by the drug solution (p < 0.05), with low systemic absorption. Among the formulations, AZ 2 resulted in much deeper skin penetration, with deeper dermal and epidermal layer deposition (1.388 ± 0.242 µg/cm²) compared to AZ 1 (four-fold higher, p < 0.05) and to the control drug solution (12 times more, p < 0.05). Analysis using ATR-FTIR suggested that azithromycin-loaded transethosomes improve the drug penetration by increasing the lipid fluidity and extracting lipids from the stratum corneum. Moreover, the transethosomes loaded with azithromycin demonstrated enhanced antibacterial efficacy against Staphylococcus aureus, with minimum inhibitory concentration (MIC) values that were lower than those of the free drug solution. Conclusion: The results highlight the promising potential of transethosomes as a novel topical drug delivery system for azithromycin that offers improved therapeutic effects against skin infections.