  We present a multi-layer mathematical model to describe the the transdermal
drug release from an iontophoretic system. The Nernst-Planck equation describe
the basic convection-diffusion process, with the electric potential obtained by
Laplace equation. These equations are complemented with suitable interface and
boundary conditions in a multi-domain. The stability of the mathematical
problem is discussed in different scenarios and a finite-difference method is
used to solve the coupled system. Numerical experiments are included to
illustrate the drug dynamics under different conditions.
