[Administration of glutamine and its dipeptides in parenteral nutrition. Which patients are candidates?]

Despite the fact that glutamine is not considered to be an essential amino acid, it is the amino acid found in the greatest concentration both in plasma (26%) as in skeletal muscle (75%). These levels may decrease in post-operative, trauma, or critical patients. Glutamine performs many functions in which its demand may be increased, such as: it is a precursor of the synthesis of nucleotides; it is an activator of the protein synthesis and at the same time it inhibits the degradation; it is an activator of glycogen synthesis; it is a metabolic substrate for rapidly replicating cells; it is an energy source for the enterocyte which is so important for maintaining the integrity and the function of the intestinal barrier, and the consumption thereof may be increased under conditions of stress. The administration of glutamine intravenously leads to two physical-chemical problems; the first is its low solubility in water; at 20 degrees C this is only 36 g/l, and the second problem is its low chemical stability in an aqueous solution at 22-24 degrees C, this being 11 days. This problem has led the industry to research two dipeptides of glutamine; L-alanyl-glutamine, and L-glycyl L-glutamine, both of which are much more soluble and much more stable. At present there is still a controversy regarding the dosage of glutamine and its dipeptides, with the dose being 0.19-0.29 g/kg/day of L-glutamine or its dipeptide forms, in surgical post-operative periods or to prevent bacterial translocation, and in patients who are candidates for bone marrow transplants, the administered dose has been 0.37-0.57 g/kg/day. The purpose of this study is to review the existing bibliography regarding the efficacy of L-glutamine or its dipeptides in four possible indications for its application in the daily clinical practice, such as: a) In post-operative surgical patients of major or medium surgery, glutamine or its dipeptides reduces the losses of muscular glutamine and its catabolism, showing a less negative nitrogen balance. b) Whether it avoids bacterial translocation. c) Whether it favors the response of the immunological system. d) Whether in patients who are candidates for bone marrow transplants this decreases the side effects due to chemotherapy and radiotherapy such as mucositis, or whether it decreases the number of days of neutrophil recovery. At present, on the European market there are two commercially available brands of glutamine dipeptides: Dipeptiven, by Fresenius Laboratories, Germany. A 100 ml vial which corresponds to 20 g of L-alanyl L-glutamine (8.2 g of alanine + 13.46 g of L-glutamine). This is added to the standard amino acid solution. Glamin, Pharmacia and Upjohn Laboratory, Sweden. This is an amino acid solution with 13.4% essential and non-essential amino acids which are equivalent to 22.4 g of nitrogen/l, and which contain 30.27 g L-glycyl-L-glutamine (10.27 g of glycine + 20 g of L-glutamine).