Formulation and penetration enhancement activity of sticks containing caffeine

Caffeine is a methylxanthine alkaloid that has been widely used in cosmetic products as anti-cellulite. Caffeine has a hydrophilic character. Thus it has difficulty in penetrating the lipid layer of the skin. This study aimed to formulate sticks containing emulsion and microemulsion caffeine (control stick), caffeine emulsions (emulsion stick), and caffeine microemulsion (microemulsion stick) and compare the penetration between them. Caffeine was made in the form of water in oil emulsions and microemulsion then form into sticks-shaped with the lipophilic component. All sticks were physically and chemically evaluated. The penetration of caffeine through Sprague-Dawley rat skin using Franz Diffusion Cell were tested for 12 hours. The penetration result of caffeine from control stick, emulsion stick, and microemulsion stick were 306.42 ± 34.92 μg/cm², 927.75 ± 57.38 μg/cm², and 2408.68 ± 81.65 μg/cm² respectively, with percentage 5.90 ± 0.67%, 12.76 ± 0.78%, and 35.23 ± 1.19%. Physical and chemical stability tests were performed for eight weeks at room temperature (29 ± 2°C), cold temperature (4 ± 2°C), and hot temperature (40 ± 2°C). Microemulsion stick delivered the highest cumulative amount of caffeine in penetration test for 12 hours, followed by emulsion stick and control stick. Also, all sticks showed physical and chemical relatively stable.