The solubility of calcium and phosphate in two specialty amino acid solutions

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.

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.

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.

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.