ABSTRACT
I. INTRODUCTION Because of the barrier properties of the stratum corneum and, also, depending on the physicochemical properties of the drug, transport from simple vehicles will often be insufficient to achieve therapeutic drug concentrations at the site of action. The therapeutic target may be the skin, or the local or distal subcutaneous tissues, depending on the intent for local, regional, or systemic therapy. Simple vehicles are defined as those in which the drug is at or close to saturation solubility, and neither the vehicle nor the drug has any interaction with the stratum corneum to reduce its barrier function. From this definition drug-vehicle interactions in subsaturated or saturated solutions will not be reviewed. In these simple systems, depending on the saturated solubility of the drug in each vehicle, large differences in skin penetration
can occur between vehicles that are at a fixed drug concentration. Vehicles in which the drug is at or near saturation will show enhanced drug penetration, compared with those in which the drug is subsaturated (1-3).
