Degradation of triamcinolone acetonide (TCA) in an ointment was investigated.\nTCA appeared to be concentrated in propylene glycol (PG) which in turn is dispersed\nin a lanolin-petrolatum mixture. Two predominant degradation products were identified: a\n21-aldehyde and a 17-carboxylic acid. The 21-aldehyde is formed after TCA is oxidized by\nO2, a reaction that is catalyzed by trace metals. Logically, the content of trace metals has a\nprofound effect on the degradation rate. It was shown that trace metals are extracted from\nlanolin and petrolatum by PG, increasing the concentration in PG. In accordance with these\nfindings, TCA degrades faster in PG that is present in the ointment formulation than in\nregular PG. The 21-aldehyde was confirmed to be a primary degradation product, while the\n17-carboxylic acid was identified as a secondary degradation product. Based on the\nmechanism of degradation, the ointment can be stabilized by the addition of sodium\nmetabisulfite which was shown to reside also in the PG phase within the ointment.
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