In Vitro Solubility of Calcium Glycerophosphate Versus Conventional Mineral Salts in Pediatric Parenteral Nutrition Solutions

Low-birth-weight infants requiring total parenteral nutrition receive inadequate intakes of calcium (Ca) and phosphorus (P) due to poor solubility of available mineral salts. To optimize Ca/P delivery, we tested the effects on in vitro solubility of mineral salt:calcium glycerophosphate (CaGP) versus calcium gluconate and K2HPO4 (CG + P); Ca:P ratios of 1:1 (at 12.5 and 25 mmol/L of Ca and P) and 2:1 (25:12.5 mmol/L); amino acid (AA) formulation: Aminosyn (A), Aminosyn-PF (A-PF), TrophAmine (T) or Vaminolac (V); and AA concentration (25 versus 8.3 g/L). Parenteral nutrition solutions contained 10% dextrose and vitamins and minerals typical of a neonatal prescription. Solutions were sampled at preparation, after 24 h in the neonatal unit (25 degrees C), and from before and after a 0.22-micron filter in extension tubing through which solutions were pumped at 5 ml/h within an incubator at 37 degrees C. Samples were analyzed for Ca and pH, and precipitation by spectrophotometry at 600 nm and light microscopy at x 100 magnification. The Ca concentration was unaffected by filtration. While spectrophotometry detected only gross precipitation, with light microscopy crystal formation was evident with 25 mmol/L of Ca and P as CG + P in A and T at 25 g of AA/L and in A, V, T, and A-PF at 8.3 g of AA/L. Precipitation did not occur with CaGP or CG + P at 12.5 mmol/L of Ca and P. Under in vitro conditions mimicking the neonatal unit, CaGP versus CG + P resulted in greater mineral solubility even at low AA concentrations.