Safety of glutamine-enriched parenteral nutrient solutions in humans

To determine the safety of glutamine-enriched parenteral nutrition, seven normal volunteers were admitted to the Clinical Research Center for three 5-d study periods. The subjects received infusions of parenteral nutrients containing increasing doses of glutamine (0, 0.285, and 0.570 g·kg body wt^-1·d^-1) substituted for alanine and glycine. Each study period was preceded by ≥ 2 wk of normal food intake. The diets were isocaloric (1.2× estimated basal metabolic rate) and isonitrogenous (1.5 g protein·kg^-1·d^-1) with nonprotein calories given as dextrose (38%) and fat emulsion (62%). The diets were all well tolerated and there were no untoward effects. Plasma glutamine concentrations increased significantly with glutamine administration but plateaued at concentrations ∼ 25% above control values. Ammonia and glutamate, potentially toxic metabolites of glutamine, did not change significantly with glutamine enrichment. Nitrogen balance and hormonal concentrations were unchanged during the three dietary periods. Results of mental-status examinations and continuous performance testing were normal and unchanged throughout the three periods. Glutamine-enriched parenteral nutrient solutions are well tolerated with no associated signs of toxicity in normal humans.