TOPICAL DELIVERY OF o•-TOCOPHEROL 171 25 20 •o 15 5 0 OMC OSal Control OMC gel OSal gel Control OMC OSal Control emulsion emulsion emulsion 3 3 gel 3 emulsion emulsion emulsion 1 1 1 3 3 3 Figure 4. Profiles for sunscreen formulations. Values are percent applied dose + SEM (n = 4). [•, Amount of ot-T in viable skin. [], Amount of ot-T permeated in SC + viable skin + receptor. I, Amount of ot-T permeated in receptor. trations. Figure 5 shows the profile for o•-T permeation in the skin from oleic acid and control formulations. Included are values in the viable skin and receptor and the total amount permeated, which have been described before. Oleic acid formulations were compared to control o•-T formulations using a Student's t-test (o• = 0.05). The 5% oleic acid gel 3 was compared with both the 1% oleic acid gel 3 and with control o•-T gel 3. In each case no statistically significant difference was obtained between the test and control formulation at o• -- 0.05. DISCUSSION This study shows that o•-T can be delivered into viable skin and receptor fluid from various formulations. Topical o•-T treatment results in a significant increase in o•-T 3.5E+01 3.0E+01 2.5E+01 2. 0E+01 1.SE+01 1.0E+01 5.0E+00 0. 0E+00 i i i r r r • OA Control OA gel 3 Control 5% OA OA Control solution solution gel 3 gel 3 emulsion emulsion 1 1 Figure 5. Skin profiles for oleic acid study. Values are percent applied dose e SEM (n = 4). [•, Viable skin + receptor. l, SC + viable skin + receptor.

172 JOURNAL OF COSMETIC SCIENCE concentrations in the viable skin, the stratum corneum, and the receptor fluid. Earlier studies (24) had shown the absence of detectable amounts of baseline ot-T in pig skin without any exogenous application, using an HPLC equipped with a UV detector (detection limit 0.25 lag/ml). Traber et al. (25) studied the penetration and distribution of ot-T applied on mouse skin. They found that the largest fraction of skin ot-T following topical application was not found on the surface but in the deeper subcutaneous layers. We also found that topical ot-T application markedly increased skin ot-T content. Lopez-Torres et al. (26) found topical ot-T treatment to significantly increase ot-T levels in both the epidermis (62-fold) and the dermis (22-fold) 24 h after administration. Two routes of skin absorption of ot-T have been suggested: from the stratum corneum into the epidermis and dermis and through the hair follicles by way of the pilosebaceous canal and into the outer root sheaths and eventually into the dermal tissue (27). This is the first systematic study delineating the effect of formulation factors on the permeation of ot-T. All our formulations were studied for stability using a previously established HPLC procedure immediately after formulation and two weeks of storage under ambient conditions (24). The formulations were also found to be visually stable. All the systems that we used had the ot-T in solution either in the alcoholic phase (gels) or in the oily phase (emulsions, solution). Emulsion 2, which was a microemulsion system containing IPM, showed the highest total permeation of ot-T. This was followed by IPM solution. There have been reports of IPM being a possible penetration enhancer. That could have been one of the possible reasons for better skin delivery by formulations containing IPM. However, we do not have sufficient evidence at this point to make a definite conclusion. The highest permeability of felodipine from benzyl alcohol micro- emulsions was found for that system that gave the highest solubility of the active both in microemulsion and in the apparent external phase (28). The IPM-containing micro- emulsion performed better than the benzyl alcohol-containing microemulsion. Based on the results of the ot-T permeation study, we chose gel 3, an IPM solution, and the emulsion formulation as prototype formulations for the concentration dependency study. The formulation difficulties experienced in making microemulsions precluded their incorporation in the study. To study the effect of concentration, four times lower and higher amounts of ot-T than the normally used 1% were formulated. The 1% formulations were also tested again in this study. A detectable amount of the active was found even at 0.25% concentration as early as four hours in the receptor. The skin profiles exhibited linearity and consequent dose proportionality. As the concentration of ot-T was increased in the formulations from 0.25% to 4%, proportionally greater amounts of active permeated into the skin. In addition to the numerous benefits that have been reported with ot-T administration, the direct sunscreening effect of ot-T is now being added to the growing list (29). Sunscreens used along with antioxidants have been found to give an added benefit of photoprotection. We used three prototypic formulations including gel 3, emulsion 1, emulsion 3, and two different sunscreens, OMC and octyl salicylate. Also, some sun- screens have been used as penetration enhancers themselves. Padimate O was shown to improve percutaneous absorption of testosterone and estradiol in swine. Padimate O was shown to lower the transition temperature of the stratum corneum lipids, which was postulated to result in significant increases in drug diffusivity across the skin (17,18). These authors also used novel topical spray vehicles containing Padimate O and octyl