You have full access to this open access article. This paper reviews some current methods for the in vivo assessment of local cutaneous bioavailability in humans after topical drug application.
After an introduction discussing the importance of local drug bioavailability assessment and the limitations of model-based predictions, the focus turns to the relevance of experimental studies. The available techniques are then reviewed in detail, with particular emphasis on the tape stripping and microdialysis methodologies.
Other less developed techniques, including the skin biopsy, suction blister, follicle removal and confocal Raman spectroscopy techniques are also described. Skin is the largest organ of the human body and is composed of three readily distinguishable layers: a the stratum corneum SC , which is the outermost part of the epidermis, b the living epidermis, and c the dermis, penetrated by a highly complex network of capillaries involved in the removal of drugs from the skin into the systemic circulation.
In addition, several pilosebaceous and sweat glands are dispersed throughout the skin, in various numbers and size, depending on body site. The SC is well-recognized as a heterogeneous two-compartment system of flattened keratinized cells embedded in a multilamellar lipid matrix mainly composed of neutral lipids and ceramides 1 β 4. Its main homeostatic functions are restriction of excessive water loss to the external environment, moisture retention, cell cohesion and desquamation.
In addition, SC is considered to be the rate-controlling membrane for transport of xenobiotics across the skin although, for very lipophilic molecules, partitioning into the more hydrophilic viable tissue may constitute the greater resistance 2 , 8.
