Photostability and Interaction of Ascorbic Acid in Cream Formulations |
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Authors: | Iqbal Ahmad Muhammad Ali Sheraz Sofia Ahmed Riaz Hussain Shaikh Faiyaz H M Vaid Saif ur Rehman Khattak Shakeel A Ansari |
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Institution: | (1) Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan;(2) Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Karachi, Karachi, 75270, Pakistan;(3) Faculty of Pharmacy, Hamdard University, Shahrae Madinat Al-Hikmah, Muhammad Bin Qasim Avenue, Karachi, 74600, Pakistan;(4) Tabros Pharma, F. B. Industrial Area, Karachi, 74600, Pakistan; |
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Abstract: | The kinetics of photolysis of ascorbic acid in cream formulations on UV irradiation has been studied using a specific spectrophotometric
method with a reproducibility of ±5%. The apparent first-order rate constants (k
obs) for the photolysis of ascorbic acid in creams have been determined. The photoproducts formed in the cream formulations include
dehydroascorbic acid and 2,3-diketogulonic acid. The photolysis of ascorbic acid appears to be affected by the concentration
of active ingredient, pH, and viscosity of the medium and formulation characteristics. The study indicates that the ionized
state and redox potentials of ascorbic acid are important factors in the photostability of the vitamin in cream formulations.
The viscosity of the humectant present in the creams appears to influence the photostability of ascorbic acid. The results
show that the physical stability of the creams is an important factor in the stabilization of the vitamin. In the cream formulations
stored in the dark, ascorbic acid undergoes aerobic oxidation and the degradation is affected by similar factors as indicated
in the photolysis reactions. The rate of oxidative degradation in the dark is about seventy times slower than that observed
in the presence of light. |
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