Direct estimation of the permeation of topical excipients through artificial membranes and human skin with non-invasive Terahertz time-domain techniques.

Background: Drug permeation through skin, or a synthetic membrane, from locally acting pharmaceutical products can be influenced by the permeation behaviour of pharmaceutical excipients.

Objective: Terahertz time-domain technology is investigated as a non-invasive method for a direct and accurate measurement of excipients permeation through synthetic membranes or human skin.

Methods: A series of in-vitro release and skin permeation experiments of liquid excipients (e.