Chemical stability of fluocinolone acetonide ointment and fluocinonide cream diluted in emollient bases.

The chemical stability of fluocinolone acetonide ointment and fluocinonide cream was studied when diluted in emollient bases. Fluocinolone acetonide ointment was diluted 1 in 4 with Unguentum Merck and Lipobase. Fluocinonide cream was also studied in these bases, with the addition of Metosyn Diluent, at dilutions of 1 in 4 and 1 in 10. Regression analysis gave the time for 5% degradation of fluocinolone acetonide at a dilution of 1 in 4 in Unguentum Merck and in Lipobase as 12 weeks in both cases. The lower 95% confidence bound of each regression line was used to set shelf lives, for additional safety, and gave values of 1 month for the Unguentum Merck dilution and 2 months for the Lipobase dilution. Fluocinonide dilutions were more stable than the corresponding fluocinolone acetonide dilutions, with no degradation detectable during the study. The base made no observable difference to stability. Shelf lives, based on the lower 95% confidence bound of the regression data, of more than 6 months would be feasible for all of the fluocinonide 1 in 4 dilutions studied and for the 1 in 10 dilution in Unguentum Merck. However, for fluocinonide 1 in 10 in Metosyn Diluent, a shelf life of only 6 weeks could be assured, due to there being more variation in the analytical results. There were insufficient data to determine a storage life based on the lower 95% confidence bound of the regression for fluocinonide 1 in 10 in Lipobase. More data would be required to determine if there was significant interbatch variation in the stability of the dilutions.