Transungual Drug Delivery: A Promising Route to Treat Nail Disorders
Transungual therapy is considered to be highly desirable to treat nail disorders due to its localized effects, improved adherence which results in minimal adverse systemic events. However, the effectiveness of topical therapies is limited due to minimal drug permeability through the nail plate. Nail permeability is quite low and limits topical therapy to early/mild disease states such as Onychomycosis, Leuconychia, Onychogrypos and Onychatrophia etc. Hence the absorption of drugs into the nail unit, to the nail plate, is highly desirable to treat nail disorders. The nail plate behaves like a concentrated hydrogel to permeating molecules and diffusion of molecules through the nail plate has been compared to the diffusion of non-electrolytes through polymer gels. For optimal transungual permeation and uptake of drug, drug molecules must be small in size and should remain non-ionic form. Current review on nail permeation focuses on the anatomy of a human nail, diseases related to nail plate, altering the nail plate barrier by means of chemical treatments, penetration enhancers as well as physical and mechanical methods used to enhance the topical bioavailability of the drugs across the nail and latest trends in drug delivery across the nail. The factors, which affect uptake of drug and permeation through the nail plate such as solute molecular size, hydrophilicity/hydrophobicity, charge, and the nature of the vehicle, are discussed. Limitations of transungual drug permeability studies and available topical therapies are discussed here.