Iontophoretic drug delivery across the nail

Introduction: Topical drug delivery to treat nail diseases such as onychomycosis and psoriasis is receiving increasing attention. Topical nail delivery is challenged by the complicated structure of the nail and the low permeability of most drugs across the nail plate. Considerable effort has been directed at developing methods to promote drug permeation across the nail plate. Iontophoresis efficiently enhances molecular transport across the skin and the eye and is now being tested for its potential in ungual delivery. Areas covered: This review covers the basic mechanisms of transport (electroosmosis and -migration) and their relative contribution to nail iontophoresis as well as the key factors governing nail permselectivity and ionic transport numbers. Methodological issues concerning research in this area are summarized. The data available in vivo on nail iontophoresis of terbinafine specifically are reviewed in separate sections. Expert opinion: Our understanding of nail iontophoresis has improved considerably since 2007; most decisively, the feasibility of nail iontophoresis in vivo has been clearly demonstrated. Future work is required to establish the adequate implementation of the technique so that its clinical efficacy to treat onychomycosis and nail psoriasis can be unequivocally determined.