COSMETIC FORMULATIONS WITH ARGIRELINE® 159 damental consideration for user acceptability), heat stability, and rheological character­ istics over time and at different temperatures. MATERIAL AND METHODS MATERIALS The products used as components in our formulations were: • Argireline® (acetyl hexapeptide-8), Batch Fl460/04, supplied by Lipotec (Barcelona, Spain). • Neo PCL o/w Autoemulsionable® (cera alba, stearyl heptanoate, cetearyl octanoate, cetyl palmitate, stearyl alcohol, steareth-7, steareth-10, stearyl caprylate, isopropyl myristate, myristyl alcohol, dimethicone, paraffinum liquidum), Batch 0512651, supplied by Roig Farma-Fagron (Terrasa, Spain). • Tefose 2561 (PEG-6 stearate, Ceteth-20, glyceryl stearate, Steareth-20), Batch 0503697, supplied by Roig Farma-Fagron (Terrasa, Spain). • Cyclomethicone pentamer (cyclopentasiloxane), purity 99.26%, Batch 0509565, sup­ plied by Roig Farma-Fagron (Terrasa, Spain). • Sorbitol 70%, Ph. Eur., purity 70.1 %, Batch 0405020, supplied by Roig Farma­ Fagron (Terrasa, Spain). • Glycerol, Ph. Eur., purity 99.8%, Batch 05F0204, supplied by Roig Farma-Fagron (Terrasa, Spain). • Hispagel 200®, Batch 0409242, supplied by Roig Farma-Fagron (Terrasa, Spain). • Propylene glycol, Ph. Eur., water content 0.1 %, Batch 04K23FP, supplied by Roig Farma-Fagron (Terrasa, Spain). • Phenonip® (phenoxyethanol, methylparaben, butylparaben, ethylparaben, propyl­ paraben), Batch 0510592, supplied by Roig Farma-Fagron (Terrasa, Spain). • Kathon CG® (methylchloroisothiazolinone 1.5%, methylisothiazolinone 0.37%), pu­ rity 75.2%, Batch 0504885, pH 2.6. • Deionized distilled water, supplied by Interapothek (Murcia, Spain). METHODS Preparation of formulations. We prepared an oil/water emulsion for normal-to-dry skin and a cream for oily skin. Argireline® is sold under the brand name Lipotec® as a transparent aqueous solution that contains 0.5 g/1 acetyl hexapeptide-8, 0.5% Phenonip®, and 99.45% water. It was refrigerated upon arrival at the laboratory and kept at 4°C, and added cold to all formulations at a concentration of 5 % Argireline® solution. The compositions of the cream and gel formulations are listed in Table I. The cream was prepared by weighing the ingredients of the oil and water phases, heating the oil phase until all components had melted, heating the water phase to the same temperature under gentle shaking to ensure homogeneity, and obtaining the emulsion by adding the water phase to the oil phase. The system was stabilized by gentle shaking while the formulation cooled to room temperature. The gel was prepared by weighing all ingredients, slowly adding water, and shaking gently (to avoid the formation of bubbles) until a gel had formed. The formulations were

160 Formula Gel Cream JOURNAL OF COSMETIC SCIENCE Table I Formulas for the Gel and Cream Formulations with Argireline® Composition Hispagel 200 25% Propylene glycol 3% + Argireline® 5% Phenonip 0.3% Water to a volume of 100 ml Oil phase Neo PCL 0/W 23% Tefose 1.5% Cyclomethicone pentamere 2% Water phase Sorbitol 4% Glycerine 4% Kathan 0.1% Water to a volume of 100 ml + Argireline® 5% stored at 4°C and room temperature (25°C). To prepare cream and gel we used a propeller Heidolph RZR 1. Organoleptic characteristics. Organoleptic characteristics were classified with descriptive terms (12) as thick, hard, creamy, smooth, soft, dry, thin, spreadable, cool, or warm. The cream and gel were scored for color, odor, texture, consistency, and appearance (exudates) 24 h after preparation and after storage at both temperatures for 30, 60 and 90 days, six months, and 12 months. pH. Chemical stability was evaluated as pH during storage for three months to predict the behavior of the formulations in contact with human skin. To measure pH we used a Crison 501 digital pH/mV-meter with the electrode for viscous samples. Rheological characteristics. The rheological properties of the formulations were studied as viscosity, a parameter closely related with stability (13). Assays were run at increasing shear rates in a Brookfield DV II+ viscosimeter (Brookfield Engineering Laboratories, Stoughton, MA) connected to a PC with the appropriate software. Rheological data were recorded periodically during a maximum period of 30 days. Stability. The activity of Argireline® peptide was studied as the effect of temperature on the stability of the active principle. Samples of the commercially available Argireline® solution were stored at 25°C, 40°C, and 60°C in an incubator for 24 h, and activity was then determined with high-performance liquid chromatography. In vitro release Assays with no membrane. To avoid manipulations and vehicles that might interfere with the cutaneous release of Argireline®, we studied release from the gel and cream formulations in vitro. In this study we tested diffusion in a system with no membrane, in which the excipient and the receptor phase were in direct contact (14, 15 ). Both formulations were also studied in an in vitro release system that simulated the physi­ ological conditions of drug desorption (16). To simulate these conditions, the formu­ lations were placed in a 32°C bath at 60 rpm in the release media phosphate-buffered solution (PBS) at pH 5.6. Release was measured by spectrophotometry over time and at