Topical formulations with superoxide dismutase: influence of formulation composition on physical stability and enzymatic activity.

Three different topical formulations were supplemented with superoxide dismutase (SOD) and evaluated concerning physical and chemical stabilities in order to determine the most stable formulation that would maintain SOD activity. Physical stability was evaluated by storing the formulation at room temperature, and at 37 and 45 degrees C for 28 days. Samples were collected at 7-day intervals for assessment of rheological behavior. Chemical stability was evaluated by the measurement of enzymatic activity in formulations stored at room temperature and at 45 degrees C for 75 days. The formulations showed a pseudoplastic behavior, with a flow index of less than 1. There was no significant difference in the initial values of flow index, hysteresis loop or minimum apparent viscosity. The simple emulsion and the one stabilized with hydroxyethylcellulose showed decreased viscosity by the 21st day and with higher temperature, but no significant changes concerning the presence of SOD. Although there were no significant changes concerning storage time or temperature, the formulation stabilized with hydroxyethylcellulose showed a marked loss of SOD activity. The addition of SOD to the formulations studied did not affect their physical stability. Simple emulsions or emulsions stabilized with carboxypolymethylene seem to be better bases for enzyme addition than emulsion stabilized with hydroxyethylcellulose.