JHSM UNUD Journals, p-ISSN: e-ISSN: 28 Abstract Alpha-mangostin is a xanthonoid compound contained in mangosteen rind (Garcinia mangostana L.) and has an antibacterial effect against Staphylococcus aureus, the bacterium that causes acne. In this study, mangosteen rind extract is formulated in a gel dosage form. This study aimed to determine the optimum formula, the physical and chemical properties as well as the optimum formula release profile of the gel dosage form of mangosteen rind extract. The mangosteen rind extract gel formula consists of viscolam, propylene glycol, glycerin, microcare®, ethyl acetate extract of mangosteen rind, and distilled water. The formula was optimized by varying the concentrations of viscolam (2% and 5%), propylene glycol (5% and 20%) and glycerin (2% and 15%) using a factorial experimental design program called Design Expert 7.0.0. The 8 formulas were developed into gel dosage form and the physical and chemical properties were then evaluated. The evaluation tests include viscosity, dispersive power, and pH tests. The evaluation results were processed using the Design Expert 7.0.0 program to determine the optimum formula. The results of the analysis showed the optimum formula of gel dosage form of mangosteen rind extract with viscolam percentage of 4.97%, propylene glycol of 9.91%, glycerin of 12.23%, microcare® of 0.3%, TEA (q.s), ethyl acetate extract of mangosteen rind of 1%, and distilled water of 45%. The evaluation results of the physical and chemical properties of the gel optimum formula revealed the viscosity of 2,345 cps, dispersive power of 6.59 cm, and pH of 6.74. Alpha-mangostin release test on the optimum formula revealed a flux value of 41.327 μg/cm 2 /t 1 / 2 . From these results, it is concluded that the optimum formula has met the physical and chemical characteristics of a good gel. Keywords: alpha-mangostin, factorial experimental design, flux, gel I. INTRODUCTION Mangosteen (Garcinia mangostana L.) is one of the plants having antibacterial activity against acne-causing bacteria such as Staphylococcus aureus [1] as it contains α- mangostin compounds in its rind [2]. The use of antibacterial activity on the dosage form used for the skin is more effective when made into a topical dosage form compared to the oral one because it can provide a local effect on the skin [3]. One of the dosage forms that can be used topically is a gel form. Gel dosage form has many advantages compared with other topical dosage forms as it contains water which makes it feel cold, cool, moist, easy to use, easily absorbed by the skin, thus providing a faster effect [4]. In addition, the high water content in the gel can reduce the risk of further inflammation due to the buildup of fat in the pores, where skin lipids can be fractionated by lipase produced by bacteria into free fatty acids. These fatty acids can cause tissue inflammation that is also one of the factors causing acne [5]. One type of gelling agents that can produce a good gel base is Sodium Polyacryloydimethyl Taurate or better known as viscolam. Based on the research conducted by Budiputra (2013), the use of viscolam at a concentration of 5% resulted in a gel with stable viscosity and pH compared to HPMC, CMC Na, carboxymethyl chitosan and carbomer 940 [6]. In addition, the resulting gel has clear, soft, and a flowable characteristic which makes it easily poured. Viscolam as a gelling agent can be used in the concentration range from 0.3% to 5% [7]. Glycerin at a concentration of 5-15% serves as a cosolvent. The addition of glycerin at a certain concentration can increase the solubility of α-mangostin in the water as a gel solvent and helps obtain gel with stable physical properties. The addition of cosolvent onto gel formula can also affect the physical properties of the dosage form. Based on the study by Sukmawati (2013), it is known that the increase of the glycerin concentration can raise the viscosity of the gel significantly [8]. Another major component in the preparation of the gel dosage form is humectants. The effect of the addition of Ketut Widyani Astuti 1 , Ni Putu Ayu Dewi Wijayanti 1 , I Gusti Ngurah Jemmy Anton Prasetia 1 , Dewa Ayu Ferianta Sari 1 1 Department of Pharmacy, Faculty of Mathematics and Natural Sciences, Udayana University ketutwidyani@gmail.com DEVELOPMENT OF GEL DOSAGE FORM OF ETHYL ACETATE EXTRACT OF MANGOSTEEN RIND (Garcinia mangostana L.)