Research Techniques Made Simple: Drug Delivery Techniques, Part 1: Concepts in Transepidermal Penetration and Absorption

Abstract

INTRODUCTION In dermatology, topical therapies are usually the first line and mainstay of treatment for the majority of skin conditions. Most topical preparations are available in a variety of potencies and delivery systems. Practitioners must carefully choose from this vast array based on the potency required, location of intended use, product elegance, and likelihood of patient compliance. Unfortunately, information concerning which preparation is truly best, regarding actual penetration and delivery to the site of action, is not readily available. In general, many practitioners believe that ointments and foams enhance penetration when compared to creams, gels, and powders. However, this is not always the case. Aside from vehicles, there are a variety of chemical and physical enhancement techniques that influence topical penetration. As physician-scientists, dermatologists should be aware of the basic mechanisms involved in topical absorption and should be able to assess whether a preparation is likely to exert its desired effect. In this article, we explore the inherent properties of the epidermis and the physiology of passive diffusion and aim to clarify the definition of the terms “absorption” and “penetration.”