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 (antioxidants), 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-mouthed beakers, incubated in a 37+/-2 degrees 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 >or=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 N(2)) 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.