A Review on Permeation Enhancer of Microemulsion Gels for Transdermal Drug Delivery System

Transdermal drug delivery systems (TDDS) offer a non-invasive, controlled-release alternative to conventional drug administration routes, enhancing patient compliance and therapeutic efficiency. Among modern delivery strategies, microemulsion-based gels (MBGs) have emerged as a promising platform, particularly for poorly bioavailable or short half-life drugs like Tapentadol Hydrochloride (TPHCl). TPHCl, a centrally acting analgesic, faces limitations such as low oral bioavailability and frequent dosing due to its short half-life. The incorporation of TPHCl into microemulsion systems not only improves its solubility and skin permeability but also enables sustained drug release when integrated into gel matrices. This review highlights the rationale, formulation strategies, characterization parameters, and therapeutic potential of microemulsion-based gels in enhancing transdermal delivery of TPHCl. We discuss key formulation components—including oils, surfactants, and co-surfactants—critical physicochemical considerations, drug release kinetics, and stability aspects. The review further explores the role of MBGs in overcoming the stratum corneum barrier and their capability to establish a reliable in vitro–in vivo correlation (IVIVC). These findings collectively suggest that microemulsion-based gels hold significant promise as innovative carriers for transdermal delivery of Tapentadol and similar pharmacological agents.