ADEQUACY OF SULFUR AMINO-ACID INTAKE IN INFANTS RECEIVING PARENTERAL-NUTRITION

Taurine and cysteine are considered essential nutrients for the infant receiving parenteral nutrition (PN). To define the adequacy of sulfur amino acid content in a pediatric amino acid formulation, evaluation of urinary excretion, fractional excretion, and balance studies for taurine, total (free + bound) cyst(e)ine (cysteine + cystine), and methionine were completed under steady-state conditions of energy and protein intake in 18 preterm infants receiving PN. These infants had a mean gestational age of 34.5 +/- 2.4 weeks, postnatal age of 19 +/- 18 days, weighed 2.1 +/- 0.5 kg, and received 100 +/- 22 kcal/kg/day and 2.8 +/- 0.1 g/kg/day of amino acids. Plasma concentrations for the sulfur-containing amino acids were within the reference range; however, the excretion and fractional excretion of taurine (3.7 +/- 7.8 mg/kg/day, 17 +/- 15%) and cyst(e)ine (12.0 +/- 7.1 mg/kg/day, 33 +/- 19%) were at the upper limits of normal reported experience. Methionine excretion (0.9 +/- 1.0 mg/kg/day) and fractional excretion (16 +/- 22%) were within normal reported experience. For taurine, fractional excretion inversely correlated with weight at the time of study (r = -0.59, P < 0.001), while for total cyst(e)ine and methionine, no correlation could be found for gestational age, postconceptional age, or weight, Taurine excretion may be a result of varying renal maturity in the study infants, and dosing may need to be adjusted based on renal maturity. Excessive dosing may explain cysteine excretion, while methionine excretion and fractional excretion suggest appropriate dosing.