FACTORS INFLUENCING THE STABILITY OF ASCORBIC ACID IN TOTAL PARENTERAL NUTRITION INFUSIONS

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Abstract
Ascorbic acid stability in TPN [total parenteral nutrition] infusions in 3-l plastic bags was examined. Vitamin C degraded slowly in mixtures which do not contain trace elements. In the presence of Cu, degradation proceeded rapidly until dissolved O2 was depleted. Reducing the Cu concentration had only a minor influence on degradation rate. This Cu-catalyzed reaction was prevented if Cys was present in the TPN regimen. The amount of ascorbic acid degraded depended on the dissolved O2 content of the infusion, the amount of residual air in the bag after filling and the permeability of the plastic to O2. In the absence of Cu, 20-30 mg ascorbic acid was broken down within 24 h at ambient temperatures, but if Cu was present, 150-200 mg was degraded within 2-4 h. The contribution of dehydroascorbic acid to the amount of vitamin C delivered to the patient was negligible. Evidently, either vitamin C and trace element injections containing Cu should not be added to the same bag, or an adequate coverage of ascorbic acid must be included to allow for losses by oxidation before and during administration.

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