N-acetyl-L-tyrosine as a tyrosine source in adult parenteral nutrition

Abstract

BACKGROUND: N-acetyl-L-tyrosine (NAT) is commonly used in place of tyrosine in parenteral nutrition, but human studies carried out to date indicate considerable amounts of it are excreted unchanged in the urine. NAT retention has not been well studied in parenterally fed adults. METHODS: NAT retention was measured in 13 adults receiving continuous parenteral nutrition with Aminosyn II 15% (Abbott Laboratories, Abbott Park, IL). RESULTS: Approximately 35% of administered NAT was excreted unchanged in the urine, with no important effect of infusion rate, N balance, or level of renal function on this value. Sufficient NAT was retained that the prescription of 1 g total amino acids/kg x day(-1) using this product exceeded the combined recommended dietary allowance for aromatic amino acids CONCLUSION: As used in the clinical setting, the phenylalanine and NAT composition of Aminosyn II is sufficient to meet the combined aromatic amino acid needs of adults with normal phenylalanine hydroxylase activity.

Some parenteral amino acid products use N-acetyl-l-tyrosine (NAT) instead of tyrosine. Patients receiving Aminosyn II excreted approximately 35% of infused NAT unchanged in their urine. Despite this loss, sufficient phenylalanine was provided and NAT retained to meet the total aromatic amino acid requirement of persons with normal phenylalanine hydroxylase activity.