The Solubility of Calcium and Phosphate in Two Specialty Amino Acid Solutions

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 fmal 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°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°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-PO 4 solubility limits and prevent precipitation of TPN solutions formulated with NephrAmine or Hepatamine. (Journal of Parenteral and Enteral Nutrition 20:63-66, 1996)