250 107.8 100 90 80 70 60 %T 50 40 30 20 10 4.0 2000.0 1900 1800 JOURNAL OF COSMETIC SCIENCE !� I 1700 1600 1500 1400 cm-1 1300 1200 1100 1000 900 800 700.0 Figure 3. ATR-FTIR spectra of aminophylline in stratum corneum after 60-min treatment with plant and essential oils. (a) 5% aminophylline/30% corn germ oil. (b) 10% peppermint oil/30% corn germ oil. (c) 10% jojoba oil/30% corn germ oil. "i .c cD C. CD ... (J 40 35 30 25 20 15 10 5 o-......---- Corn germ Olive Jojoba Peppermint Ytang Oil enhancers Lilacin Rosemary Figure 4. Comparative values of peak height decrease of aminophylline in the stratum corneum after 60-min treatment with plant and essential oils.

� 40 � 30 tG & .s 4) 20 Hl ..._ � 0 SKIN PENETRATION OF AMINOPHYLLINE Cream 8 Formulation$ 251 • r='� ;..�"""'j .. �-·········�.1'•.•....,• �=9 ;..---. � :.. .. -��=:���{ t::r:::J Cream C Figure 5. Comparative values of peak height decrease of aminophylline in the formulations: Cream A (containing 50% ethanol), cream B (containing [3-cyclodextrin enhancer), and cream C (containing 1-methy 1-2-pyrrolidone enhancer). nophylline components had penetrated the stratum corneum (Figure 5), and N-H absorbance at 1557 cm- 1 decreased 44.43%, 17.27%, and 27.9% for creams A, B, and C, respectively. The enhancement effect of 5 0% ethanol demonstrated the largest increase in perme­ ability when the three chemical enhancers were used, since ethanol directly affects the skin's modification of the formulation. Thus, it can modify the intercellular lipid do­ mains to reduce the barrier resistance of the bilayer lipids. In addition, penetration enhancement can be indirect by modification of the thermodynamic activity of the vehicle. Rapid permeation of a good solvent from the donor solution, such as ethanol, can leave the permeant in a more thermodynamically active state than when the solvent was present (16). A study also reports a linear relationship between the flux and thermody­ namic activity of the drug in the vehicle with various concentrations of ethanol (17). However, the high delivery rate of ethanol enhancers often produces skin irritation. Aminophylline absorption using l-methyl-2-pyrrolidone was less than with 50% etha­ nol by a factor 1.6, and greater than with �-cyclodextrin by a factor of 1.6. One-methyl- 2-pyrrolidone has a heterocyclic ring structure, which is a five-membered ring, and �-cyclodextrin consists of six, seven or eight glucose units linked together into a ring. One-methyl-2-pyrrolidone, which has a smaller ring and polar molecule, is thought to allow easier intercalation on the tightly packed lipids of the stratum corneum and a greater disruption of these lipids, increasing lipid fluidity. Based on previous studies