The stability of ascorbic acid in TPN mixtures stored in a multilayered bag.

Because of the susceptibility of some vitamins to oxidation, they are not normally added to TPN mixtures until shortly before addministration. Vitamin C (ascorbic acid) is oxidised rapidly, especially in the presence of trace elements. The aim of this study was to investigate the stability of ascorbic acid in complete TPN mixtures in Ultrastab multilayer bags, which are designed to reduce oxygen transmission and thus oxidation, in comparison with standard EVA bags. Ascorbic acid content was determined in two typical TPN mixtures providing 16 g nitrogen, 2000 kilocalories, electrolytes, trace elements and multivitamins, with and without fat emulsion, during storage at 5 degrees C for up to 3 months. In EVA bags ascorbic acid degraded by more than 75% during 24 h and was undetectable in 2-3 days. In contrast, there was a comparatively small initial loss of 15-30% ascorbic acid in mixtures stored in multilayer bags, with little further loss during 1-3 months. Bags containing fat emulsion retained higher concentrations of ascorbic acid after storage compared to those without fat emulsion, but all mixtures in multilayer bags maintained 60-80% ascorbic acid activity after 3 months. Since ascorbic acid is the most oxygen-sensitive vitamin, complete TPN mixtures with vitamins could be compounded in multilayer bags for an extended shelf life, rather than admixing just prior to administration.