Assessing retinol stability in a hydroquinone 4%/retinol 0.3% cream in the presence of antioxidants and sunscreen under simulated-use conditions: a pilot study

Background: Retinol (ie,vitamin A) is commonly used in dermatology as an adjunct to treat rhytids, acne,and dyschromia. However, vitamin A and many of its derivatives have poor photostability and are unstable in the presence of oxygen. Objective: We aimed to assess the stability of retinol under simulated patient application conditions in a commercially available hydroquinone 4% cream containing retinol 0.3%, avobenzone (ultraviolet-A sunscreen), octinoxate (ultraviolet-B sunscreen), vitamins C and E (aantioxidants), and moisturizers. Methods: One gram of the preparation was applied as a thin film to the inside base of 4 groups of four 100-mL wide-mmouthed beakers, incubated in a 37 ± 2°C water bath. Each experimental group consisted of 4 beakers for assays at 0.5,1,2,and 4 hours. The samples were exposed to varying combinations of full spectrum light and headspace gas (air or inert nitrogen gas [N2 ]). Retinol content was assayed via high-pressure liquid chromatography using a 1:9 water:methanol solvent system. The control group (group 5) was not exposed to full-spectrum light or headspace gas but served for comparative purposes. Results: On exposure to light and room air, retinol stability was 94.4% at 0.5 hour,94.8% at 1 hour, 92.4% at 2 hours, and 91.5% at 4 hours. The retinol contained in the preparation was stable for ≥4 hours. Samples exposed to light and N 2 gas demonstrated 96.5% and 91.3% stability at 0.5 hour and 4 hours exposure times, respectively. Samples that were not exposed to light had a stability of 99.2% (group 3, exposed to air) and 96.9% (group 4, exposed to N₂) of the initial retinol present after 4 hours. Conclusion: The retinol in the hydroquinone 4%/ retinol 0.3% cream with antioxidants and sunscreens underwent <10% degradation under simulated-use conditions, including exposure to UV light, oxygen, and body temperature.