Primary Children's Medical Center, University of Utah School of Medicine, Salt Lake City 84113, USA.
BACKGROUND: The purpose of this study was to determine precipitation limits and construct curves for calcium and phosphorus in parenteral nutrition solutions compounded with specialty amino acid solutions. METHODS: The effect of temperature, concentration of amino acids, and pH on the solubility of calcium and phosphate was studied for two specialized amino acid solutions: NephrAmine and HepatAmine. Ten amino acid solutions were manufactured with NephrAmine and 12 with HepatAmine at amino acid concentrations of 0.8%, 1.5%, and 2%. The final dextrose concentration was 10%. Some of the solutions were tested with the additive cysteine hydrochloride, 40 mg cysteine/g of protein, and some were buffered with sodium bicarbonate or hydrochloric acid to model the pH of a combined fat emulsion and total parenteral nutrient (TPN) solution. Calcium gluconate and potassium phosphate were added to test samples of each TPN solution. A range of calcium concentrations of 2.5 to 40 mEq/L and phosphate concentrations of 2.5 to 40 mmol/L were tested. After storage at room temperature (25 degrees C) for 18 hours, solutions were inspected for precipitation. At the end of the 18-hour period, the solutions were held in a water bath at 37 degrees C for 30 minutes and inspected for precipitation and microcrystallization. RESULTS: Solubility curves were plotted to represent Ca-PO4 solubility limits before visual or microscopic precipitation. These curves depend on the variables of time, temperature, concentration, and pH. CONCLUSIONS: These data and graphs will help the clinical pharmacist estimate Ca-PO4 solubility limits and prevent precipitation of TPN solutions formulated with NephrAmine or Hepatamine.