ABSTRACT
Introduction .................................................................................................................................... 319 Ability to Screen a Large Number of Formulations................................................................... 321 Use of a Surrogate End Point That Is Quick, Easy, and Independent of the
Physicochemical Properties of the Model Permeant............................................................. 321 Low Incubation Times to Further Increase the Throughput and Hence Time Efficiency....... 321 Minimal Use of Test Chemicals and Efficient Utilization of Model Membrane such
as Animal Skin ........................................................................................................................ 322 Adaptability to Automation to Reduce Human Interference .................................................... 322 Use of a Common Model Membrane to Represent Human Skin ............................................. 322 Use of Consistent Thermodynamic Conditions for Enhancer Formulations............................ 322
Overview of INSIGHT Screening................................................................................................... 322 Skin Impedance-Skin Permeability Correlation............................................................................ 324 Validation of INSIGHT with FDC................................................................................................... 327 Applications of INSIGHT Screening .............................................................................................. 327 References....................................................................................................................................... 330
The idea of delivering drugs through the skin is as old as human civilization, but the excitement has increased in recent times after the introduction of the first transdermal patch in 1970s. Though transdermal route of drug administration offers several
advantages — reduced first-pass drug metabolism, no gastro-intestinal degradation, longterm delivery (>24 h) and control over delivery and termination — only few drug molecules have been formulated into transdermal patches (Barry, 2001). The cause of this imbalance between the benefits of this route and the number of products in the market lies in the skin itself. The skin’s topmost layer, stratum corneum (SC), forms a barrier against permeation of xenobiotics into the body and water evaporation out of the body. This barrier must be altered to maximize the advantages of transdermal route of drug administration. This has engaged pharmaceutical scientists, dermatologists, and engineers alike in research over the last couple of decades (Mitragotri, 2004). High research activity in this field has led to the introduction of a variety of techniques including formulation-based approaches (Williams and Barry, 2004), iontophoresis (Kalia et al., 2004), electroporation (Prausnitz, 1999; Weaver et al., 1999), acoustical methods (Mitragotri and Kost, 2004), microneedles (Prausnitz, 2004), jet injection (Hingson and Figge, 1952), and thermal poration (Sintov et al., 2003).
