Advances in Microemulsion Drug Delivery: From Fundamentals to Therapeutic Applications

Microemulsion-based drug delivery systems are increasingly attracting attention in the pharmaceutical field owing to their remarkable capacity to enhance solubility, stability, and bioavailability, as well as enable targeted drug delivery. These systems comprise clear, stable, isotropic blends of oil, water, and surfactant, often accompanied by a co-surfactant. Their appeal to pharmaceutical scientists lies in their versatility as effective drug-delivery vehicles, accommodating a diverse array of drug molecules. Microemulsions have demonstrated effectiveness in protecting fragile drugs, controlling drug release, enhancing solubility, increasing bioavailability, and reducing variation in patient response. Moreover, formulations suitable for various routes of administration have been successfully devised. Since their discovery, microemulsions have gained prominence, becoming increasingly vital in both academic research and industrial settings due to their distinct characteristics, such as reduced interfacial tension, extensive interfacial area, thermodynamic stability, and the ability to solubilize otherwise immiscible substances. Transparent appearance, low viscosity, and inherent thermodynamic stability set microemulsions apart from conventional emulsions. This review aims to elucidate the potential of microemulsions as delivery vehicles and to provide insights into their formation principles. Additionally, it comprehensively explores microemulsion-based drug delivery systems, encompassing oral, topical, transdermal, ocular, and parenteral delivery methods, with a focus on recent advancements, existing challenges, and future trajectories.