The influence of positive or negative charges in the passive and iontophoretic skin penetration of porphyrins used in photodynamic therapy

Fluorescence microscopy photomicrographs of vertical slicing of rat skin. The red color illustrates drugs' skin permeation. Iontophoresis enhanced the delivery of the negative drug, TPPS4, only to the superficial layers of rat skin, while structurally similar but positive TMPyP was transported in higher amounts to deeper skin with homogeneous distribution when the electric current was applied.