What is true about Glutamine in total parenteral nutrition (TPN)?

Glutamine in Total Parenteral Nutrition: Key Facts and Clinical Importance

Glutamine is a substrate for gluconeogenesis and is not an essential amino acid under normal conditions, but it should be supplemented in total parenteral nutrition (TPN) for critically ill patients to improve clinical outcomes. 1

Characteristics of Glutamine

Glutamine has several important physiological roles:

• It is the most abundant free amino acid in the body 1
• Under normal conditions, it is not an essential amino acid as it has an endogenous production rate of 50-80g/24h in adults 1
• It serves as a substrate for gluconeogenesis (conversion to glucose) 1
• It functions as a carrier for nitrogen and carbon between organs 1
• It increases intestinal cellularity by maintaining intestinal structure and function 2
• It acts as a precursor for nucleotides and provides cellular protection through glutathione and heat shock proteins 1
• It regulates ammonia and acid-base balance 1

Glutamine in Total Parenteral Nutrition

Clinical Importance

• Glutamine is typically supplied in total parenteral nutrition for critically ill patients 1
• During critical illness, increased demand for glutamine utilization (for immune activity and repair) is not adequately met by endogenous production, causing plasma levels to fall 1
• Low plasma glutamine levels are associated with worse outcomes 1
• Glutamine supplementation in TPN has shown significant benefits:
  • Reduced mortality risk (RR 0.67, CI 0.48-0.92) 1
  • Reduced infections 1
  • Improved glycemic control 1
  • Maintained intestinal function and prevented intestinal atrophy 2

Practical Administration

• L-glutamine is poorly soluble and degrades during heat sterilization, so it was historically omitted from TPN 1
• Modern TPN uses glutamine-containing dipeptides (alanyl-glutamine or glycyl-glutamine) which are more stable and soluble 1
• Recommended dosage: 0.2-0.4 g/kg/day of L-glutamine (equivalent to 0.3-0.6 g/kg/day of alanyl-glutamine dipeptide) 1
• Doses in the range of 10-30g glutamine/24h have been safely tolerated 1

Clinical Considerations and Caveats

• Glutamine supplementation should be considered specifically in patients who cannot be fed adequately enterally and require exclusive parenteral nutrition 1
• Recent evidence has questioned the universal application of glutamine supplementation for all critically ill patients 1
• High-dose administration of glutamine in critically ill patients with organ dysfunction has been associated with increased mortality 1
• The benefits of glutamine supplementation may be more pronounced with parenteral administration compared to enteral administration 1

Conclusion

Among the options presented, the correct statement about glutamine is that:

• It is supplied in total parenteral nutrition (TRUE)
• It increases intestinal cellularity (TRUE)
• It is not an essential amino acid under normal conditions (TRUE)
• It is a substrate for gluconeogenesis (TRUE)

All of these statements are correct based on the evidence provided, making glutamine a multifunctional amino acid with important clinical applications in nutritional support for critically ill patients.