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Harokopio University of Athens
University of Southern California
Nutritional support is the delivery of formulated enteral or parenteral nutrients to appropriate patients for the purpose of maintaining or restoring normal levels of nutritional status. Preterm and sick term infants frequently require total parenteral nutrition (TPN).
The most sterile and efficient method of parenteral nutrition is the all-in-one (AIO) method, where all of the essential nutrients in their respective concentration are combined into one solution and administered together. The AIO parenteral admixtures have been proven to be advantageous both clinically and economically.(1) The number of nurse handlings and manipulations of the central venous catheter and the risk of thrombophlebitis and errors are reduced, and all nutrients are supplied continuously over the day.(2) These preparations are more sterile due to reduced exposure to foreign molecules and particles that would occur if separate solutions were mixed. The main difficulties in forming an AIO parenteral nutrition admixture are the problem of increased particle size, due to the formation of lipid globules and insoluble salt precipitates, and the presence of toxic degraded forms of vitamins and amino-acids, which accumulate in the solution.(3) Many studies have been conducted that showed the stability of AIO parenteral admixtures in the treatment of adults. However, in neonates, due to differences in the final composition of the admixtures, smaller blood vesicles and incapability to withstand the same amounts of toxic substances in the bloodstream as a child or an adult, there is still no agreement on the definition of stability and on which type of admixture should be given.
Degradation of vitamin C
Vitamins are unstable compounds that can possibly produce toxic degradation products, resulting in the loss of clinical efficacy.(4) Ascorbic acid (vitamin C) is the least stable vitamin in TPN mixtures and it is incompatible with many drugs. In addition, it degrades and darkens on exposure to light, and it is rapidly oxidised by air and in alkaline media. The most important mechanism of degradation is that of oxidation to inactive products. The amount of ascorbic acid degraded depends on the dissolved oxygen content in the TPN mixture, the amount of residual air in the bag after filling, the permeability of the plastic to oxygen and the storage time.(5)
Trace elements, in particular copper, but also iron and zinc, catalyse the oxidation reaction. In the presence of copper, the degradation of ascorbic acid occurs until dissolved oxygen is depleted, and 150–200mg will be lost within two to four hours. In the absence of copper, only 20–30mg of ascorbic acid are degraded within 24 hours. Cysteine, however, chelates heavy metals such as copper and thus reduces the rate of ascorbic degradation. Hence, the use of amino acid solutions containing cysteine helps to minimise ascorbic acid loss.(6) Loss of vitamin C also increases with pH and, hence, when mixed with amino acid solutions of high pH.(7)
Materials and methods
Stability studies were carried out on two compounded AIO admixtures for neonates. Admixtures were prepared in ethyl-vinyl acetate (EVA) plastic bags using automatic system filling at the IASO Maternity Hospital in Athens. Four protocols were created according to the gestational age of the infant (below 26 weeks, 26–28 weeks, 29–32 weeks and 33–40 weeks) through collected literature and clinical experience of the authors. The nutritional requirements of a neonate gestational age below 26 weeks and above 33 weeks are different. These two extremes, which were chosen for testing, correspond to two different formulations (see Table 1) and represent a broad range of weights found in infants.
Two separate AIO admixtures were prepared, and samples of each were studied at two different temperatures, 4˚C (storage) and 25˚C (compounding), and were then analysed at starting time, 24 hours, 48 hours and seven days after compounding. The loss of vitamin C was determined using high-performance liquid chromatography (HPLC). HPLC analysis was carried out on an Agilent Technologies (formerly Hewlett-Packard) series HP 1050 system equipped with an autosampler, and a HP1046A fluorescence detector connected to a HP integrator and a HP Chemstation. A Nucleosil 120-5 C18 column (Macherey-Nagel) was used. After liquid–liquid extraction for the preparation of the sample for analysis, reversed-phase HPLC, resulting in detection of tocopherols, was performed as previously described by Lazzarino et al.(8)
Results and discussion
The ascorbic acid loss in AIO parenteral admixtures A and B after being stored at 4(˚)C and at room temperature for several time periods is presented in Table 2. In both admixtures the highest possible loss determined was about 30%, compared with the initial vitamin amounts calculated by HPLC. This loss was observed after storage of admixtures for seven days.
In this study, two different compounded formulae have been compared for their stability of vitamin C by HPLC in the course of time at different storage temperatures. Although no significant loss of vitamin C was observed with different temperatures, a significant loss was seen over time. As it is currently advisable to avoid coadministering vitamins and divalent ions, not many investigations have taken place to prove the stability of vitamin C in TPN mixtures. Thus, TPN mixtures containing vitamin C should be administrated until up to 24 hours after preparation, where the loss is not significant.
The inclusion of large excesses of ascorbic acid in TPN mixtures to compensate for degradation losses may result in significant amounts of oxalic acid (a decomposition product of ascorbic acid) being formed, which is a cause for concern as it can react with calcium ions, forming calcium oxalate, which then precipitates out of solution and is toxic.(9) The formation of a precipitate will depend on the amount of ascorbic acid and on its rate of degradation, on calcium concentration and on the pH and amino-acid profile of the solution.(10) Further research must be carried out to assure the suitability of administrating the AIO admixtures to neonates.