EVALUATION OF IN VITRO PERCUTANEOUS ABSORPTION OF GLYCYRRHETINIC ACID FROM NANOEMULSIONS OBTAINED BY THE PHASE INVERSION TEMPERATURE (PIT) METHOD Carmelo Puglia 1 , Manuela Liotta 1 , Markus Drechsler 2 , Luisa Rizza 1 and Francesco Bonina 1 1 Dipartimento di Scienze Farmaceutiche, Università di Catania,Viale A.Doria 6, 95100 Catania, Italy 2 Macromolecular Chemistry II, University of Bayreuth, Germany INTRODUCTION Nano-emulsions are innovative colloidal systems endowed with interesting features such as high kinetic stability, low viscosity and optical transparency which make them very attractive in many dermatological applications. Nano-emulsions have been developed to overcome some limitations of microemulsions, such as the high surfactant concentration required for their formation and their scarce stability against sedimentation and creaming. Furthermore their small droplet size ensure high stability against flocculation and coalescence phenomena. Nano-emulsions can be prepared by spontaneous emulsification such as phase inversion temperature (PIT) emulsification or phase inversion composition, or by using a shear device [1]. Recently nano-emulsions have been studied as an interesting alternative to more traditional carriers for efficient delivery of active ingredients through the skin. In fact due to their small size, they can penetrate through the “rough” skin surface enhancing the penetration of substances. Therefore these vehicles could be used as an efficient tool for topical administration of actives which scarcely cross the skin. Glycyrrhetinic acid (GA) is an ingredient used in cosmetic field as lenitive and anti-reddening agent but characterized by some unsuitable physicochemical properties that drastically influence its percutaneous absorption profile. The present paper aims to assess the ability of nanoemulsion obtained by PIT method in increasing GA in vitro percutaneous absorption. EXPERIMENTAL METHODS Materials Emulgin B2 (Ceteareth-20), Emulgade SE-PF (Glyceryl stearate/ Ceteareth-20/ Ceteareth- 12/ Cetearyl alcohol/ Cetyl palmitate), Cetiol CC (Dicaprylyl carbonate), Cetiol LC (Caprylic capric acid of saturated fatty alcohols C 12-18 ) and alpha- bisabolol were obtained from Cognis S.p.A (Como, Italy). 18-β-glycyrrhetic acid (glycyrrhetinic acid) was a gift of A.C.E.F. S.p.A. (Piacenza, Italy). Transcutol CG (Ethoxydiglycol) was obtained by Gattefossè (Milan, Italy). Carbopol 934P ® (CTFA: Carbomer), BFGoodrich (Cleveland, Ohio, USA). All other materials were of analytical grade. Production of nanoemulsions by phase inversion temperature (PIT) method Nanoemulsions were produced following a method reported elsewere [2], adding glycyrrhetinic acid (0.5%) to the oil phase. The samples were rapidly brought to 25°C (under manual stirring), using a ice-bath to achieve fast cooling. Conventional O/W emulsion containing the same amount of glycyrrhetinic acid were used as reference topical form. Characterization of nanoemulsions Droplet size determination Droplet size analysis of the nanoemulsions was performed by photon correlation spectroscopy (PCS) by using a Zetamaster (Malvern Instrument Ltd, Sparing Lane South, Worcs, England) equipped with a solid state laser having a nominal power of 4.5 mW with a maximum output of 5 mW 670 nm. Analyses were performed using a 90° scattering angle and at 20 (± 0.2) °C. Cryo-TEM A 2μl drop of solution was placed on a pure thin bar 600-mesh TEM grid and blotted with filter paper until it was reduced to a thin film (10-200 nm) spanning the hexagonal holes of the TEM grid. The sample was then vitrified by liquid ethane. The vitrified specimen was transferred to a Zeiss EM922 transmission electron microscope for imaging using a cryoholder (CT3500, Gatan). Specimens were examined with doses of about 1000-2000 e/nm 2 at 200 kV. Images were recorded digitally by a CCD camera (Ultrascan 1000, Gatan) using a image processing system (GMS 1.4 software, Gatan). In vitro diffusion studies For in vitro diffusion studies, samples of adult human skin (mean age 36 ± 8 years) from breast reduction operations were processed in order to obtain stratum corneum/epidermis (SCE) membranes [3]. In order to prepare the membranes, subcutaneous fat was carefully trimmed and the skin Proc. 5th World Meeting on Pharmaceutics, Biopharmaceutics and Pharmaceutical Technology, Geneva, 27–30 March 2006