A Novel Herbal Nano-Based Ear Drop with Ocimum gratissimum Essential Oil: An Alternative Strategy for Managing Otomycosis

Background/Objectives: Otomycosis is a recurrent fungal infection of the external auditory canal. This disease is difficult to manage with current antifungal agents due to irritation, ototoxicity risk, and emerging resistance. Natural essential oils have been proposed as alternatives, yet their clinical application in otic formulations remains limited due to their poor solubility and stability. In this study, we report the first ear-drop formulation combining microemulsified Ocimum gratissimum essential oil and acetic acid for otomycosis treatment. Methods: The essential oil was quality-validated with eugenol content superior to 60%. A systematic formulation study was performed, and the Tween 20/isopropanol (4:1, w/w) mixture was selected as the optimal surfactant system, yielding a stable microemulsion with high encapsulation efficiency (~98%) and relevant physicochemical stability (up to 28 days). The final formulation containing 1% acetic acid and 0.3% micro-emulsified essential oil met pharmacopeial requirements in terms of appearance, pH, viscosity, and microbial limits. Results: Importantly, this micro-emulsified eardrop demonstrated significantly greater in vitro antifungal activity than 3% boric acid and 2% acetic acid eardrops in twelve clinical fungal isolates from Vietnamese swimmers, especially on Curvularia, Cunninghamella, Aspergillus terreus, and Bipolaris. Although less pronounced than 1% clotrimazole, the finalized formulation demonstrates better antifungal kinetics and a broader activity spectrum. Conclusions: This work provides relevant experimental evidence on the use of Ocimum gratissimum essential oil in a microemulsion delivery system and demonstrates its efficacy against clinically relevant otomycosis pathogens. The results establish a foundation for future in vivo and clinical studies.