Stabilizing agents ascorbic acid

The decomposition of ascorbic acid is catalyzed by trace metal ions in solution, hence the addition of sequestering agents such as EDTA and its salts has been shown to enhance the stability of ascorbic acid (291,292,293),... 

N-Nitrosamine inhibitors Ascorbic acid and its derivatives, andDC-tocopherol have been widely studied as inhibitors of the N-nitrosation reactions in bacon (33,48-51). The effect of sodium ascorbate on NPYR formation is variable, complete inhibition is not achieved, and although results indicate lower levels of NPYR in ascorbate-containing bacon, there are examples of increases (52). Recently, it has been concluded (29) that the essential but probably not the only requirement for a potential anti-N-nitrosamine agent in bacon are its (a) ability to trap NO radicals, (b) lipophilicity, (c) non-steam volatility and (d) heat stability up to 174 C (maximum frying temperature). These appear important requirements since the precursors of NPYR have been associated with bacon adipose tissue (15). Consequently, ascorbyl paImitate has been found to be more effective than sodium ascorbate in reducing N-nitrosamine formation (33), while long chain acetals of ascorbic acid, when used at the 500 and lOOO mg/kg levels have been reported to be capable of reducing the formation of N-nitrosamines in the cooked-out fat by 92 and 97%, respectively (49). 

In connection with the antioxidant properties of L-ascorbic acid and its stability, many kinetic and mechanistic studies have been performed. For instance, it has been shown a role as a radical scavenger in the autooxidation of methyl linoleate, and its synergistic effect when used with vitamin E.362 The photooxidation,363 superoxide-mediated oxidations,364 reactions with radicals,365 and the influence of other agents, including ultrasound and y-rays,366 have been reported. 

At 30°C in the absence of Arg, the ferrous-oxi complex transforms very slowly to the ferric state. In the presence of substrate and H4B, a new species with the 12-nm shifted Sorey band is detected. A decay of this species is accompanied by the formation ofN -hydroxy-L-arginine. Because the presence of HUB is necessary for these reactions, the main function of this compound is to be a reducing agent. This suggestion is supported by experiments on the stabilizing effect of ascorbic acid on the chemical stabilization of tetrahydropterin in the endothelial nitric oxide synthesis (Heller et al., 2001). At the same time, a significant increase in the half lifetime of H4B in solution is demonstrated. As is shown (Wei et al., 2001), a ferrous-dioxy intermediate in iNOS forms for 53 s 1 and then is transformed to the [S-Fe(IV)=0] state. The rate of the [S-Fe(IV)=0] decay is equal to the rate ofH4B radical formation and the rate of Arg hydroxylation. In contrast,... 

Ranganathan [4] enhanced the stability of MRI contrast imaging agents by incorporating ascorbic acid, (VI), to diminish oxidation of substituents from free radical reactions induced by radionuclide decay. 

Buffers can also be provided in parenteral formulations to ensure the required pH needed for solubility and/or stability considerations. Other excipients included in parenteral products are preservatives (e.g., benzyl alcohol, p-hydroxybenzoate esters, and phenol), antioxidants (e.g., ascorbic acid, sodium bisulfite, sodium metabisulfite, cysteine, and butyl hydroxy anisole), surfactants (e.g., polyoxyethylene sorbitan monooleate), and emulsifying agents (e.g., polysorbates). An inert gas (such as nitrogen) can also be used to enhance drug stability. Stability and solubility can also be enhanced by the addition of complexation and chelating agents such as the ethylenediaminetetraacetic acid salts. For a more detailed list of approved excipients in parenteral products, the reader should consult the monographs within the USP. 

Ascorbic acid Antioxidant, buffering agent, stabilizer iv, im, sc, ia... 

Ascorbic acid is used as an antioxidant in aqueous pharmaceutical formulations at a concentration of 0.01-0.1% w/v. Ascorbic acid has been used to adjust the pH of solutions for injection, and as an adjunct for oral liquids. It is also widely used in foods as an antioxidant. Ascorbic acid has also proven useful as a stabilizing agent in mixed micelles containing... 

In powder form, ascorbic acid is relatively stable in air. In tbe absence of oxygen and other oxidizing agents it is also heat stable. Ascorbic acid is unstable in solution, especially alkaline solution, readily undergoing oxidation on exposure to the air. The oxidation process is accelerated by light and heat and is catalyzed by traces of copper and iron. Ascorbic acid solutions exhibit maximum stability at about pH 5.4. Solutions may be sterilized by filtration. 

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