What dose and form of cysteine is used for parenteral nutrition in preterm infants to address solubility concerns?

• A. Cysteine HCl at 40 mg per gram of amino acids
• B. Cysteine base at 60 mg per gram of amino acids
• C. L-Cystine at 20 mg per gram of amino acids
• D. Cysteine sulfate at 10 mg per gram of amino acids

Answer: (A)

In neonatal parenteral nutrition, cysteine is added mainly to improve the solubility of calcium and phosphate in the solution by acidifying it. The form used is cysteine hydrochloride because the hydrochloride salt lowers the solution’s pH effectively, helping minerals stay dissolved at the concentrations used for preterm infants. The recommended dosing is about 40 mg of cysteine per gram of amino acids, which provides enough cysteine for metabolic needs while maintaining solubility and stability of the PN admixture. Using other forms—cysteine base, L-cystine, or cysteine sulfate—does not offer the same reliable solubility benefit or stability in the PN solution, so they are not used for this purpose.