Factors affecting the stability of L-glutamine in solution

The degradation rate of L-glutamine in water, various buffers, and intravenous solutions was assessed over a period of 2 weeks. Measurements were made at various temperatures (22-24 degrees C, and 4 degrees C and -80 degrees C) and pH, and also in the presence and absence of light and oxygen (intravenous solutions only). At 22-24 degrees C, the degradation rate of glutamine was variable depending on the type of solution used (0.23% in water pH 6.5; 0.22% in dextrose/water [15% w/v]; 0.8% in mixed total parenteral nutrition (TPN) solution), and on the pH, molarity and type of buffer used. The degradation rate was essentially unaffected by light and O(2). The degradation rate of L-glutamine in the intravenous solutions was less than 0.15%/day at 4 degrees C, minimal at -20 degrees C (<0.03%/day), and undetectable at -80 degrees C. Glutamine degradation resulted in the equimolar formation of ammonia and no associated formation of glutamate. It is concluded that (a) glutamine degradation in solution is variable due to the effect of physico-chemical factors, and (b) glutamine degradation in TPN solutions is sufficiently slow, especially during storage at 4 degrees C or below, to consider its inclusion in such solutions, for clinical use.