Objectives: A positive effect of glutamine (GLN) in critically ill patients was described in various studies. However the effect of glutamic acid (GLU), which can be a precursor of GLU, is not known. The aim of the present study was to compare the effect of parenteral nutrition enriched with GLU or GLN on plasma concentrations and clearance of both amino acids. Methods: Sixteen patients requiring total parenteral nutrition were studied in a prospective, randomized, crossover study. They received randomly parenteral nutrition enriched with GLU (19.6 g per day) or GLN (13.5 g of GLN and 4.1 g of GLU per day) for one week at random. The plasma aminogram was analyzed 2 hours and 7 days after the onset of the respective regimen. Metabolic clearance of amino acids was expressed as the rate of amino acid infusion divided by plasma level. Results: Basic biochemical parameters and nitrogen balance were not different in the respective infusion regimes. The increase of GLU administration from 4.1 g per day to 19.6 g per day led to significant rise in GLU clearance (219.2 ± 93.8 ml ⋅

        Key words: glutamic acid, glutamine, amino acid clearance, nitrogen balance, parenteral nutrition.