Photostability and interaction of ascorbic acid in cream formulations

Area of Science:

• Pharmaceutical Sciences
• Physical Chemistry
• Cosmetic Science

Background:

• Ascorbic acid (vitamin C) is a vital antioxidant used in topical formulations.
• Its stability in cream bases is crucial for efficacy but challenging due to degradation pathways.

Purpose of the Study:

• To investigate the kinetics and factors influencing ascorbic acid photolysis in cream formulations.
• To compare photolytic degradation with oxidative degradation in the dark.

Main Methods:

• Spectrophotometric analysis was employed to study ascorbic acid photolysis kinetics.
• Apparent first-order rate constants (k(obs)) were determined under UV irradiation.
• Factors such as active ingredient concentration, pH, viscosity, and formulation characteristics were evaluated.

Main Results:

• Photolysis rate constants were determined, with dehydroascorbic acid and 2,3-diketogulonic acid identified as photoproducts.
• Ascorbic acid photolysis was influenced by ionized state, redox potentials, pH, and cream viscosity.
• Physical stability of the cream formulation was found to be critical for vitamin stabilization.
• Oxidative degradation in the dark occurred via similar factors but was approximately 70 times slower than photolysis.

Conclusions:

• Ascorbic acid's photostability in creams is significantly affected by formulation properties and its physicochemical state.
• Cream viscosity and physical stability play key roles in minimizing both photolytic and oxidative degradation.
• Understanding these factors is essential for developing stable and effective topical vitamin C formulations.