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

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. NAT retention was measured in 13 adults receiving continuous parenteral nutrition with Aminosyn II 15% (Abbott Laboratories, Abbott Park, IL). 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 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.