Role of L-glutamine in critical illness: new insights

This review will attempt to summarize recent clinical and experimental data on glutamine's use in critical illness. It will try to present the concept of glutamine as a 'drug' or 'nutraceutical', given in addition to standard nutritional support.

Glutamine, traditionally considered to be a nonessential amino acid, is now considered as 'conditionally essential' following critical illness and injury. States of critical illness lead to significant decreases in plasma levels of glutamine and when this decrease is severe it has been correlated with increased mortality. Laboratory data have demonstrated numerous benefits of glutamine in experimental models of critical illness, including attenuated proinflammatory cytokine expression, improved gut barrier function, enhanced ability to mount a stress response, improved immune cell function, and decreased mortality. Over the last 10 years clinical trials of glutamine supplementation in critical illness have shown benefit with regard to mortality, length of stay, and infectious morbidity. However, data demonstrating a lack of benefit with glutamine supplementation in the critically ill have been presented as well. It appears that dose and route of administration clearly influence the benefit observed from glutamine administration, with high-dose, parenteral glutamine demonstrating an advantage over low-dose, enteral glutamine.

High-dose or parenteral (>0.20-0.30 g/kg/day or > or =30 g/day) glutamine appears to demonstrate the greatest potential for benefit in critically ill patients. No evidence of harm has been observed in studies conducted to date, thus further clinical trials utilizing glutamine as a pharmacologic supplement to standard nutrition are warranted.