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j. Cosmet. Sci,, 52, 225-236 (July/August 2001) Effect of formulation on the delivery and metabolism of -tocopheryl acetate MEERA RANGARAJAN and JOEL L. ZATZ, Schering Plough Research institute, Kenilworth, NJ 07033-0530 (M.R.), and Rutgers-The State University of New Jersey, Department of Pharmaceutics, College of Pharmacy, 160 Fmlinghuysen Road, Piscataway, NJ 08854-8020 •. R. Z.). Accepted for publication April 15, 2001. Data contained in this paper were presented at the Annual Scientific Seminar of the Society of Cosmetic Chemists, Toronto, Ontario, May 11-12, 2000. Synopsis The effect of delivery system on the permeation and metabolism of o•-tocopheryl acetate (o•-TAc) was studied in micro-Yucatan pig skin, which closely resembles human skin. Various o•-tocopheryl acetate formulations, including a simple isopropyl myristate (IPM) solution, an o/w emulsion, microemulsions, which diffbred in their oily phase content, and alcoholic and hydroalcoholic gels were made. A suitable HPLC method was developed and validated to separate and quantify o•-TAc and o•-tocopherol (o•-T). Dulbecco's modified phosphate-buffered saline with 3% bovine serum albumin (DMPBS-BSA 3%) served as the receptor media to ensure tissue viability and to maintain skin conditions. Finite doses (5 pl) of the formulations were applied to viable pig skin using a statistically approved randomized complete block design. Data were analyzed using Tukey's studentized range test, and interday variability was estimated using an F-test. About 70% of the active was recovered from the wash, representing the amount adhering to the surface of the skin. o•-TAc underwent metabolism in pig skin to the active antioxidant, o•-T. The identity of the HPLC peaks were confirmed by spiking studies using known standards. The extent of metabolism was found to be formulation-dependent. No o•-T was, however, detected in the stratum corneum. A higher extent of metabolism was obtained for the IPM solution, a microemulsion containing IPM as the oily phase, and the hydroalcoholic gel, when calculated based on the percent of total o•-TAc permeated in the viable skin. Metabolism occurred in pig skin to the extent of 15-20% in terms of the total amount of o•-TAc permeated in the viable skin and stratum corneum. Thus the topical delivery and metabolism ofo•-TAc were found to be dependent on formulation. INTRODUCTION The involvement of free radicals in skin damage including sunburn, photoaging, and photocarcinogenesis has led to the use of antioxidants such as o•-tocopherol (o•-T) in various skin preparations. o•-T acts primarily as a lipophilic radical-scavenging antioxi- dant and suppresses chain initiation and/or chain propagation steps by donating its 225