The influence of amino acid source on the stability of ascorbic acid in TPN mixtures

This study was undertaken to investigate the stability of ascorbic acid and its primary degradation product, dehydroascorbic acid, in total parenteral nutrition (TPN) mixtures. The influence of the type of bag and the commercial source of amino acid on ascorbate degradation was examined, using a stability-indicating high-pressure liquid chromatography (HPLC) method. Ascorbic acid was most stable in multilayered bags, compared with ethylvinyl acetate (EVA) bags. Results indicated that, in multilayered bags, the initial rapid ascorbic acid degradation was greatest in TPN mixtures containing amino acid infusions without reducing activity. In contrast, degradation in TPN mixtures containing amino acids with reducing compounds (Vamin 14 and Freamine III 8.5%) was less than 10% of the added amount. Dehydroascorbic acid degraded approximately in parallel with ascorbic acid, and it contributed to the total available ascorbate activity. The addition of air to TPN mixtures in multilayered bags caused accelerated degradation of both ascorbic acid and dehydroascorbic acid. It is concluded that TPN mixtures compounded in multilayered bags can be safely assigned extended shelf lives, especially if compounded using an amino acid with reducing activity. This is principally due to the protective effect of the bag wall in preventing oxygen transmission, the cause of ascorbic acid oxidation, because oxygen transmission through the bag wall is minimized during storage. TPN mixtures stored in EVA bags should be administered within 2-4 d of compounding, depending on the amino acid infusion used.