PHOSPHATIDYLCHOLINE AS PENETRATION ENHANCER 373 3OO 250 •- 200 o "• 150 E Q- 100 o• 50 = 1% PC ......... • .... 2% PC + 4%PC 0 5 10 15 20 25 Time(hr) Figure 9. Effect of phosphatidylcholine concentration on the skin permeation of caffeine. can be interpreted that phosphatidylcholine itself can act as a permeation enhancer, its mechanism more closely connected with modulating skin barrier function than with vesicular delivery. In fact, most of the caffeine molecules in the formulation were located in the continuous phase and not in the vesicles because of caffeine's water solubility and leakage from the vesicles. Oil-soluble materials may lead to different results because they tend to remain in the vesicles. However, phosphatidylcholine is a reliable, mild, skin permeation enhancer that can be used in cosmetic products. REFERENCES (1) J. L. Zatz, Optimizing skin delivery, Cosmet. Toiletr. 115, 31-35 (2000). (2) J. W. Wiechers, Avoiding transdermal cosmetic delivery, Cosmet. Toilerr. 115, 39-46 (2000). (3) S. Magdassi and E. Touitou, Novel Cosmetic Delivery Systems (Marcel Dekker, New York, 1999), pp. 1-97. (4) Y. Yokomizo and H. Sagitani, Effects of phospholipids on the percutaneous penetration of indometh- acin through the dorsal skin of guinea pigs in vitro, J. Contr. ReL, 38, 267-274 (1996). (5) Y. Yokomizo and H. Sagitani, The effects of phospholipids on the percutaneous penetration of indomethacin through the dorsal skin of guinea pig in vitro. 2. The effects of the hydrophobic group in phospholipids and a comparison with general enhancers, J. Contr. ReL, 42, 37-46 (1996).

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