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J. Cosmet. Sci., 58, 245-254 (May/June 2007) Vehicle and enhancer effects on human skin penetration of aminophylline from cream formulations: Evaluation in vivo LAI-HAO WANG, CHIA-CHEN WANG, and SU-CHING KUO, Department of Applied Chemistry, Chia Nan University of Pharmacy and Science, Tainan 71710, Taiwan R.0.C. Accepted for publication March 6, 2007. Synopsis The effects of four essential oils (rosemary, ylang, lilacin, and peppermint oils), and three plant oils (jojoba oil, corn germ oil, and olive oil) on the permeation of aminophylline were studied using human skin. The permeation effects of these oils were compared with those of three chemical penetration enhancers. Although all oils enhanced the permeation of aminophylline, their effects were less than that of ethanol. Jojoba oil was found to be the most active, causing about a 32% peak height decrease of N-H bending absorbances in comparison with the control, while peppermint, lilacin, rosemary, and ylang oils caused 28%, 24%, 18%, and 12% peak height decreases, respectively. Microemulsions containing 10% jojoba oil and 30% corn germ oil were found to be superior vehicles for the percutaneous absorption of aminophylline. Comparision with results obtained from high-performance liquid chromatography shows good agreement. INTRODUCTION Theophylline is a xanthene derivative. When theophylline is combined with ethylene diamine in anhydrous alcohol, it forms the compound aminophylline (1). Aminophylline has been reported to break down fat and cellulite from cells by triggering enzymes that help the body to release fat from stores in certain areas of the body. It works well on the thighs and buttocks of women and has a smoothing effect on the skin. However, some individuals suffer from allergic reactions to ethylenediamine hydrochloride (2). The aminophylline cream has been studied by Fourier transform infrared FTIR (3), electro­ chemical detection (4), reversed-phase high-performance liquid chromatography (HPLC) (5), and spectral analysis (6). There was only one study applied to aminophylline cream, in which permeation through rat skin in vitro was performed in a two-compartment diffusion cell to a select enhancer (7). Human skin is usually the preferred skin mem­ brance to use in an absorption study. No animal model gives absorption values identical to those obtained in human skin (8). The stratum corneum has long been considered a major barrier to the penetration of topically applied chemicals. Studies have Address all correspondence to Lai-Hao Wang. 245