Study of Vitamin B6 in Total Parental Nutrition

Abstract

Two novel reverse phase high performance liquid chromatography methods for the analysis of pyridoxine have been developed, capable of detecting pyridoxine below concentrations of 500 microgram/L. One assay involves a mobile phase of pH 2.5with the detection of pyridoxine by UV at 291nm. It  is used for measuring pyridoxine in Total Parenteral Nutrition (TPN) mixtures containing Vamin 9 and Vamin 9 glucose. The second assay has a mobile phase of pH 6.75 with UV detection at 324 nm, and is used for measuring pyridoxine concentration in all TPN solutions except those containing Vamin 9 or Vamin 9 glucose. Both assays show a linear response to concentration with correlation coefficients of 0.99 for both assays, and coefficients of variation of 2.6% for the first assay and 2,4% for the second assay. The stability of pyridoxine was followed in various constituent TPN solutions and in complete TPN regimen solutions, Pyridoxine was shown to be stable in all constituent solutions, in the absence of water soluble vitamins, in the light and dark, except in Intralipid solutions, In solutions containing water soluble vitamins(Solivito), pyridoxine was stable in the dark but rapidly degraded in the light in dextrose 10% and saline 0.9% infusion solutions. The addition of trace element solution (Addamel) statistically significantly stabilised pyridoxine to the effect of light (P < 0,001 by student’s t-test). In amino acid solutions, pyridoxine degraded in the light in solutions of low amino acid content (Vamin 9 Glucose, Aminoplex 12 ) but was statistically significantly more stable in solutions of high amino acid content(Aminoplex 24, Vamin 18) (P<0.001) by student’s t-test. In Intralipid solutions ,pyridoxine showed a slow degradation in both the light and the dark, This was statistically significantly increased on dilution (P < 0,001 by student's t-test) and in diffused sunlight (P < 0.001 by students t-test). In complete TPN regimen solutions, pyridoxine was statistically significantly more stable in the light than in diffused sunlight (P < 0.001 by student’s t-test), Pyridoxine was stable for seven days when the TPN solution was protected from light by an opaque outer cover, and when stored in a refrigerator. The stability of pyridoxine was followed in solutions containing riboflavin and found to degrade. The rate of degradation was dependent on riboflavin concentration.  The majority of patients referred for TPN were found to have serumpyridoxal-5-phosphate (PLP) concentrations below the stated reference range (20-80nmol/L) before starting TPN. After one week of receiving 2mg pyridoxine daily via continuous TPN infusion, the majority of patients had serum PLP concentrations in the lower half of the normal range. It is, therefore, suggested that patients receive a dose of 4mg daily or higher or a ‘stat? dose of 10-20mg pyridoxine hydrochloride at the start of TPN, or both.