Influencing factors and drug application of iontophoresis in transdermal drug delivery: an overview of recent progress

Transdermal drug delivery is limited by the stratum corneum of skin, which blocks most molecules, and thus, only few molecules with specific physicochemical properties (molecular weight < 500 Da, adequate lipophilicity, and low melting point) are able to penetrate the skin. Recently, various technologies have been developed to overcome the strong barrier properties of stratum corneum. Iontophoresis technology, which uses a small current to improve drug permeation through skin, is one of the effective ways to circumvent the stratum corneum. This approach not only provides a more efficient, noninvasive, and patient-friendly method of drug delivery but also widens the scope of drugs for transdermal delivery. In this review, the mechanisms underlying iontophoresis and affecting factors are outlined. The focus will be on the latest advancements in iontophoretic transdermal drug delivery and application of iontophoresis with other enhancing technologies. The challenges of this technology for drug administration have also been highlighted, and some iontophoretic systems approved for clinical use are described.