Graphical process design tools for iontophoretic transdermal drug-delivery devices

A graphical procedure was proposed for the optimum design of transdermal drug-delivery systems enhanced by iontophoresis. Contour plots displayed the relationships among steady-state plasma level, current density and initial drug concentration in a vehicle. This information was combined with a closed-form expression of the process time constant, estimated as the medicament in the blood reaches a plateau after application of the electric field. Analysis was conducted using Laplace-transformed variables and did not require time-domain solutions. Simulation results show that a current density of 0.044 mA/cm2 and a loading of 3500 μg/ml of dexamethasone sodium m-sulfobenzoate were necessary to achieve an equilibrium plasma concentration of 1.254 ng/cm3 with a time constant of 8.34 h.