Stability of amino acids and the availability of acid in total parenteral nutrition solutions containing hydrochloric acid

Abstract

The stability of amino acids and the availability of acid from total parenteral nutrition (TPN) solutions containing hydrochloric acid were studied. Hydrochloric acid in the concentrations of 40 (TPN 1), 60 (TPN 2), and 100 (TPN 3) meq/liter was added to TPN solutions (4.25% amino acids, 25% dextrose monohydrate) containing various electrolytes (TPN control). Amino acid concentrations were determined from one sample of each solution using a Technicon Automatic Amino Acid Analyzer. Samples were analyzed 24 hours after mixing and compared with the TPN control at 24 hours. Tryptophan was assayed using a specific colorimetric assay at 0, 6, 24, and 48 hours. The concentrations of proline (76.2 of control) and histidine (85.7% of control) wee decreased in TPN 3. This phenomenon appeared to be dependent upon the concentration of hydrochloric acid in the TPN solution. There was no appreciable loss of any of the other amino acids in the test solution as compared with the control. Tryptophan levels fell in both the TPN control and the test solutions independent of the hydrochloric acid concentration. The pH of the solutions decreased with increasing concentrations of hydrochloric acid from 5.87 in the TPN control to 3.18 in TPN 3. The titratable acidity increased with increasing concentrations of hydrochloric acid (28.21 meq/liter in the TPN control to 115.54 meq/liter in TPN 3). Concentrations of some amino acids decreased in the presence of hydrochloric acid. Because of the short-time period in which these solutions will usually be infused (4-24 hours), this probably has a negligible effect on patients' nutritional therapy. The availability of acid from these solutions makes this combination useful in treating severe metabolic alkalosis.