Calcium and phosphate compatibility in low-osmolarity parenteral nutrition admixtures intended for peripheral vein administration.

BACKGROUND Precipitation of calcium (Ca) and phosphate (P) salts can lead to potentially lethal outcomes, especially in low-osmolarity parenteral nutrition (LO-PN) formulations. Three concentrations of amino acids (AA) and 2 concentrations of calcium gluconate and sodium phosphate injections on the compatibility of Ca and P in LO-PN admixtures were studied. METHODS Final AA concentrations of 1%, 2%, or 3% (n = 3) and 5% glucose (G) were prepared with either 2.5 or 5 mmol/L (5 or 10 mEq) of Ca (n = 2) and 15 or 30 mmol/L of P (n = 2) for a total of 12 base (3 x 2 x 2) formulations. Triplicate bags of each were analyzed for subvisible micro-precipitates using the light obscuration (or extinction) method for particle counts per milliliter (PC) in the size range of 1.8-50 mum at 7 time intervals over 48 hours stored at 30 degrees C +/- 0.2 degrees C. Visual evaluation was performed using a high-intensity lamp against a black background for detection of macro-precipitates. The pH of all 36 admixtures was measured at 0 and 48 hours. Any precipitated material was isolated and characterized by polarized light microscopy and infrared spectroscopy. RESULTS Of the 12 base LO-PN formulations tested, those containing 1% and 2% AA with 5 mmol/L of Ca and 30 mmol/L of P showed significant increases in PC, and some resulted in visible dibasic calcium phosphate precipitation. Analyses of variance based on concentrations of AA, Ca, P, and time were highly significant independent variables for increases in the PC of potentially embolic particles, that is, sizes >5 mum (P < .0001). The lowest concentrations of Ca and P, 2.5 and 15 mmol/L, respectively, had significantly lower PC (P < .05) for all sizes compared with the other Ca and P combinations. CONCLUSIONS LO-PN admixtures (AA </= 3%; G = 5%) should not contain more than 2.5 mmol/L of Ca from calcium gluconate injection and no more than 15 mmol/L of P from potassium or sodium phosphates injection.