Prefilter and postfilter cysteine/cystine and copper concentrations in pediatric parenteral nutrition solutions

Pediatric amino acid products contain lower concentrations of methionine and require the addition of L-cysteine HCl just before infusion. Reports of a potential interaction between cysteine and copper, a routine addition to parenteral nutrition solutions, have appeared in the literature. This study serially evaluated cysteine/cystine and copper concentrations pre- and postfilter (0.22 microns) in two parenteral nutrition formulations prescribed for normal fluid (NF) or fluid-restricted (FR) pediatric patients. Solutions were infused via a peristaltic pump in vitro for 24 hours. Pre- and postfilter samples were obtained immediately after the infusion began (time 0) and at 1, 2, 3, 4, 8, 12, 16, 20, and 24 hours during the infusion. At 24 hours pre- and postfilter, cysteine/cystine were quantitated at 87.3% and 85% of the initial concentrations, respectively, for the NF solution and 92% and 91.5% for the FR solution. Pre- and postfilter copper was quantitated at 87.5% and 92.5% of the initial concentrations, respectively, for the NF solution and 88.2% and 95.2% for the FR solution. The 24 hour area under the curve for cysteine/cystine was 88.4% for the NF solution and 96.4% for the FR solution. For copper, the area under the curve for the NF solution was 99% and 96.7% for the FR solution. There was no visual evidence of incompatibility or precipitation. We conclude that copper-containing parenteral nutrition solutions with L-cysteine HCl added immediately before infusion are relatively stable after compounding and infusion over 24 hours.