Aging Effect on Iontophoretic Transdermal Drug Delivery

Abstract

The skin is the largest organ of the human body, offering an accessible interface for the administration of drugs. The main obstacle to transdermal drug delivery is the skin's barrier properties, due essentially to the stratum corneum, the skin's outermost layer, which is impermeable to most drugs. There are several techniques used to modify the barrier properties of the stratum corneum and to enhance the permeation of drugs through the skin. One popular approach to overcome this barrier is iontophoresis, a technique where electric fields are applied to enhance the transport, by adding an electric potential gradient to a concentration gradient. Several factors affect iontophoresis transdermal drug delivery (TDD). Among them the mechanical properties of skin play an important role. The skin behaves like a viscoelastic material, and it is well known that transport in viscoelastic media is non-Fickian. Consequently, the traditional Fickian advection-diffusion iontophoretic models are inappropriate. As aging induces huge modifications in the mechanical properties of the skin, the models presented in this paper can provide clinicians with guidelines for personalized TDD. The paper is concerned with the analysis and numerical simulation of a non-Fickian viscoelastic model for iontophoretic transdermal drug transport. A multilayer approach is followed, where the polymeric drug reservoir and the properties of the main skin layers are taken into account. Numerical simulations illustrate the effect of aging in TDD and shed light on how to include it in personalized TDD protocols.