L-Lysine Should Not Be Avoided in Preterm Newborns
There is no evidence-based contraindication to administering L-lysine to preterm newborns—in fact, lysine is an essential amino acid that must be provided to support protein synthesis and growth. The premise of this question appears to be based on a misconception, as current guidelines and research support adequate lysine provision in neonatal parenteral nutrition.
Lysine Requirements in Preterm Infants
Lysine is the first limiting essential amino acid in neonatal nutrition and cannot be synthesized by the body, making it indispensable in both enteral and parenteral feeding regimens. 1
- The parenteral lysine requirement for neonates is 105 mg/kg/day as determined by the gold standard indicator amino acid oxidation method 1
- For enterally fed term infants in the first month of life, the mean lysine requirement is 130 mg/kg/day (with confidence intervals ranging from 76.3 to 183.7 mg/kg/day) 2
- Preterm infants receiving partial enteral feeding (40% enteral, 60% parenteral) demonstrate fractional first-pass lysine uptake of 32%, which decreases to 18% with full enteral feeding 3
Why Lysine Must Be Provided
Amino acid solutions used in parenteral nutrition for preterm infants must contain lysine as part of the complete essential amino acid profile to prevent negative nitrogen balance and support protein accretion. 1, 4
- Early amino acid administration (starting from the first day of life) results in increased protein synthesis and positive nitrogen balance in preterm infants 1
- Preterm infants should receive 2.5-3.5 g/kg/day of parenteral amino acids from postnatal day 2 onwards, which inherently includes lysine as part of the complete amino acid mixture 4
- Parenterally administered lysine is less effective than dietary lysine in promoting protein deposition, but both routes are necessary depending on feeding tolerance 3
Common Misconceptions and Clarifications
The question may stem from confusion with other amino acids that have specific restrictions or supplementation guidelines in preterm infants:
- Glutamine should NOT be supplemented additionally in infants up to two years of age (Level of Evidence 1++, Recommendation Grade A) 1, 4
- Cysteine requires specific supplementation (50-75 mg/kg/day) in preterm neonates due to limited endogenous synthesis 1, 4
- Tyrosine has a minimum requirement of at least 18 mg/kg/day in preterm infants 1, 4
Clinical Implications
When prescribing parenteral nutrition for preterm infants, ensure that the amino acid solution contains a balanced profile of all essential amino acids, including lysine, at the recommended total amino acid dose of 2.5-3.5 g/kg/day. 4
- A minimum of 30-40 kcal per 1 g amino acids should be provided to guarantee amino acid utilization 1, 4
- Lysine supplementation in children and adolescents has been shown to enhance nitrogen retention, improve anthropometric measurements, and positively influence developmental outcomes 5
- The only precaution with lysine is avoiding excessive intake, which can lead to amino acid imbalances, but this applies to all amino acids, not specifically lysine 5
Important Caveat
The only lysine-containing compound that requires specific consideration in preterm infants is ibuprofen lysine (used for patent ductus arteriosus closure), which is unrelated to nutritional lysine requirements. 6 This medication is safe and effective when used at approved doses and should not be confused with nutritional lysine supplementation.