Calcium and Phosphate Solubility Curve Equation for Determining Precipitation Limits in Compounding Parenteral Nutrition.

Clinicians have published research and reports on calcium and phosphate solubility within parenteral nutrition (PN) for over 40 years. Foundational empirical laboratory investigation in the 1980s motivated by the prevalence of neonatal rickets and osteomalacia in the Neonatal Intensive Care Unit (NICU) population led to precipitation curves that have guided PN prescribing and compounding. Over subsequent decades, numerous publications have expanded the knowledge of factors influencing calcium and phosphate solubility in formulating optimal and safe PN admixtures. Failure to adhere to known principles has led to serious injury and death. Known solubility curves are derived from empiric analysis of a finite number of conditions and concentrations, whereas custom PN orders vary widely and rarely match the admixture composition in the data set used to derive the published precipitation curves. Various commercial platforms have been developed to aid the pharmacist in assessing the potential for precipitation when evaluating a PN order. Some applications plot the calcium and phosphate concentrations of the prescribed PN against known published graphs most similar to the order, allowing the pharmacist to judge the risk of precipitation. Other approaches use intellectually protected trade secret algorithms to determine calcium and phosphate solubility across a continuum of conditions. This publication reports equations that have been used successfully for over 2 decades in our regional network of NICUs and shared with others to determine safe prescribing limits for calcium and phosphate concentrations using an electronic PN prescribing program.