Amino acid stability and microbial growth in total parenteral nutrient solutions

The stability of amino acids in total parenteral nutrient (TPN) solutions stored for 30 days and the potential for stored TPN solutions to support growth of microbial contaminants were studied. Solutions of 3.5% crystalline amino acids and 25% dextrose with electrolytes were prepared either by using a commercially available amino acid solution with electrolytes or by adding electrolytes individually to a base TPN solution. Solutions were stored in polyvinyl chloride bags at refrigerated (4 degrees C) or room (25 degrees C) temperature for 30 days. Some bags were inoculated with Candida albicans or Pseudomonas maltophilia before storage to serve as positive controls for evaluation of microbial contamination. At appropriate intervals, bags of each type of solution under each storage condition were analyzed for amino acid content. Microbial growth was evaluated by filtering the contents of each bag and incubating the filter in brain-heart infusion broth. No microbial growth was detected in any of the study solutions, but all solutions inoculated with C. albicans and 2 of 16 solutions inoculated with Ps. maltophilia had evidence of growth. No significant decreases in the concentrations of any of the amino acids were noted for solutions stored at refrigerated temperature, but significant decreases in the concentrations of arginine and methionine were noted for solutions stored at room temperature. Total parenteral nutrient solutions can be stored for up to 30 days if they are kept at refrigerated temperatures and protected from light; however, quality assurance measures for these solutions should include end-product microbiologic testing.