ABSTRACT
In the course of performing in vitro percutaneous absorption studies, it is important to ensure the integrity of the stratum corneum. In vitro assessment of the permeability of chemicals is often preceded by studying the rate of penetration of tritiated water (1,2). However, this technique has several limitations. For example, it results in hydrated stratum corneum, possibly affecting the penetration of the compound under investigation. This method cannot be used if the test compound is tritium labeled. In addition, it is time-consuming and requires a license and facilities to handle radioactive materials. In practice, the repetitive measurement of tritiated water in laboratories is accomplished by determining the fraction of the dose applied absorbed at a fixed time. Selection of that fixed time is difficult without a priori knowledge of the permeability, and improper selection can lead to an erroneous assessment of the barrier properties of skin. Recently an alternate technique, which measures the electrical resistance across the skin slices, has also been proposed for this purpose (3). Based on the initial results, this technique appears to have some advantages, but more studies are required to validate it.
