Enhancing agent stability

Biotransformation and Biliary Excretion. The liver is a major site of drug metabolism, but it is also an important excretory organ. Some of the 

Chemical transformations in the liver are greatly facilitated by the action of enzymes within the smooth endoplasmic reticulum of hepatocytes (often called the microsomal fraction). Phase I reactions (oxidation, reduction, and hydrolysis reactions) convert molecules into more polar forms that usually differ in biological activity from the parent form. Oxidation reactions occur primarily under the direction of a family of enzymes called P450- Non-specific esterases in the liver, plasma, and other sites catalyze the hydrolysis of esters, whereas amides are hydrolyzed in the liver. Protein drugs are often degraded by proteases and peptidases, which are abundant in many tissues, including the intestinal tract and plasma. Phase II reactions are conjugation reactions. 

The susceptibility of agents to the action of enzymes is a major determinant of stability in tissues. Since enzyme activity is highly selective, subtle changes in the chemical structure can often lead to profound reductions in enzyme-mediated degradation. This approach is illustrated with examples involving analogs to acetylcholine and oligonucleotides. 

Glucuronidation of Ether or Ester (here shown via UDP-Glucuronic acid) 

Adapted from [9], particularly Chapter 1. These reactions can also occur in the kidney, intestinal tract, and plasma. Typical mechanisms are illustrated for some of the reactions. Reactive intermediates are enclosed in brackets. 

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One of the big drawbacks associated with the use of many conducting polymers as electrochromic materials is their low cycle life stability. To overcome this, and other electrochromic properties, many composite materials have been studied. These composites include mixtures with other optically complementary, conducting polymers and inorganic electrochromes, such as tungsten trioxide and Prussian Blue, and colour enhancing agents or redox indicators, exemplified by the inherently electrochromic indigo carmine (1.96). °... 

Function Flavor enhancer humectant nutritive sweetener texturizing agent stabilizer. 

One of the critical factors in excipient selection and concentration is the effect on preferential hydration of the biopharmaceutical product [53, 54], Preferential hydration refers to the hydration layers on the outer surface of the protein and can be utilized to thermodynamically explain both stability enhancement and denatur-ation. Typical excipients used in protein formulations include albumin, amino acids, carbohydrates, chelating and reducing agents, cyclodextrins, polyhydric alcohols, polyethylene glycol, salts, and surfactants. Several of these excipients increase the preferential hydration of the protein and thus enhance its stability. Cosolvents need to be added in a concentration that will ensure their exclusion from the protein surface and enhance stability [54], A more comprehensive review of excipients utilized for biopharmaceutical drug products is available elsewhere [48],... 

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. 

When working with this type of resist to make VLSI devices there are several problems that come up, particularly the need for improved thermal stability from the resist images emd a method to control light that is reflected or scattered in a nonimagewise manner. The function of a development enhancement agent is to increase the dissolution rate of the photoresist so that polymers with better physical properties but slow dissolution rates may be used. The dyes... 

Anionic leveling agents. Promote migration and leveling of direct, disperse, and reactive dyes on cotton and polyester/ cotton blends. Provide enhanced dispersion stability with fine particle size. Effective lubricants which minimize rope marks. 

Lai GS, Pez GP, Pesaresi RJ, Prozonic EM, Cheng H. Bis(2-met-hoxyethyl)aminosulfur trifluoride a new broad-spectrum de-oxofluorinating agent with enhanced thermal stability. J. Org. Chem. 1999 64 7048-7054. 

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. 

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