Clearance, epidermal

Siddiqui, O., Roberts, M. S., and Polack, A. E. Percutaneous absorption of steroids Relative contributions of epidermal penetration and dermal clearance. J. Pharmacokin. Biopharm. 17 405, 1989. 

The effect of age on percutaneous absorption has been examined in vivo in man with variable results. It was postulated (Roskos et al. 1989) that reduced hydration levels and lipid content of older skin may be responsible for a demonstrated reduction in skin permeability where the permeants were hydrophilic in nature (no reduction was seen for model hydrophobic compounds) (Table 14.2). The reduced absorption of benzoic acid demonstrated in the elderly (Rougier 1991) was in line with this suggestion, but not the reduction in absorption of testosterone (lipophilic) (Roskos et al. 1986), or lack of change in the absorption of methyl nicotinate (more hydrophilic) with age (Guy et al. 1983). There are a number of potential physiological changes which may be responsible for age-related alterations, including an increase in the size of individual stratum corneum corneocytes, increased dehydration of the outer layers of the stratum corneum with age, decreased epidermal turnover and decreased microvascular clearance (reviewed in Roskos and Maibach 1992). The issue of age-related variability, however, is far from resolved. 

Borisenko, G G, Iverson, S L, Ahlberg, S, Kagan, V E, and Fadeel, B, Milk fat globule epidermal growth factor 8 (MFG-E8) binds to oxidized phosphatidylserine Implications for macrophage clearance of apoptotic cells. Cell Death Differ 11 (2004) 943-945. 

Research into new peptide hormone pharmaceuticals continues along several lines. Probably the most active area of research is into alternative delivery methods such as oral, nasal, buccal, transdermal, or pulmonary. All of these alternatives share issues of barrier penetration (whether mucosal or epidermal), protein stability, rate of clearance, and bioavailability. 

Both the epidermal flux and the viable epidermal concentrations of topically applied solutes are dependent on clearance from the dermis and binding in the dermis. Factors deflning this clearance and binding have been considered in this chapter. In addition, examples of altered percutaneous absorption fluxes or tissue levels as a consequence of changes in blood flow, lymphatic flow, and altered binding have been summarized. 

Sicca syndrome Impaired salivation diminished clearance of reflux contents secretion of epidermal growth factor diminished... 

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