Surfactants absorption promoters

Neutralizing removes the large amount of hexavalent chromium from the surface of the part. Hexavalent chromium shortens the life of the catalyst, and trace amounts completely inhibit electroless nickel deposition. The neutralizer is usually a mildly acidic or basic reducing agent, but other types of neutralizers are available, especially for substrates that are difficult to plate. The neutralizer may also contain surfactants (qv) or other compounds that increase catalyst absorption absorption promoters are often needed for non-ABS plastics. 

The use of surfactants as intestinal absorption promoters is the most investigated approach. Furthermore, this chapter will review the enhancing effect of surfactants with various structures on the permeability of GI membrane to macromolecules. 

In the late 1960s, Engel and coworkers [56-58] proposed sulfated and sulfonated surfactants as absorption promoters for two biological macromolecules, heparin and insulin. In these studies, sodium lauryl sulfate (SLS) promoted the absorption of heparin but not of insulin intraduodenally administered in rats and dogs. 

Any enhancing effect of surfactants on drug absorption appears to be related to increased drug solubilization, modification of mucosal permeability, or reduction of resistance of the unstirred water layer at the GI membrane surface. In general, unionic surfactants have little effect on membrane structure but cationic surfactants have been associated with reversible cell loss and loss of goblet cells. These effects must limit consideration of surfactants as absorption promoters, particularly for long term treatment. 

A systematic study in rats, in which the absorption-enhancing effects of a number of surfactants were compared, was reported by Hirai et al (1981a,b). The promoting effect of several nonionic surfactants was paralleled by their ability to lyse red blood cells and to release protein from the nasal mucosa of rats. Bile salts, however, were found to be less lytic and damaging to the rat nasal mucosa than nonionic ether-type surfactants. Generally, a positive correlation was observed between the damaging effect on the biomembrane and the absorption-promoting effect of the surfactants. 

Sodium salicylate has been found to enhance rectal absorption of drugs [309] but contrary to the action of some surfactants the absorption promotion was not found to be the result of a permanent change in the rectal mucosa. 

There is no simple explanation of the absorption-promoting effect of the surfactant. Penetration of the surfactant into the liquid membrane seems to be... 

Humectants and low vapor pressure cosolvents are added to inhibit drying of ink in the no22les. Surfactants or cosolvents that lower surface tension are added to promote absorption of ink vehicle by the paper and to prevent bleed. For improvements in durabiUty, additional materials such as film-forming polymers have been added. Ink developments are providing ink-jet prints with improved lightfastness, waterfastness, and durabiUty. As a result, such prints are beginning to rival the quaUty of electrophotographic prints. 

These esters of p-hydroxybenzoic acid have been used primarily to prevent growth of molds but in higher concentrations possess some weak antibacterial activity. Their effective use is limited by low aqueous solubility and by reports of stinging and burning sensations related to their use in the eye. They bind to a number of nonionic surfactants and polymers, thereby reducing their bioactivity. They are used in combination, with the methyl ester at 0.03-0.1% and the propyl ester at 0.01-0.02%. Parabens have also been shown to promote corneal absorption [140]. 

The difficulty with HLB as an index of physicochemical properties is that it is not a unique value, as the data of Zaslavsky et al. (1) on the haemolytic activity of three alkyl mercaptan polyoxyethylene derivatives clearly show in Table 1. Nevertheless data on promotion of the absorption of drugs by series of nonionic surfactants, when plotted as a function of HLB do show patterns of behaviour which can assist in pin-pointing the necessary lipophilicity required for optimal biological activity. It is evident however, that structural specificity plays a part in interactions of nonionic surfactants with biomembranes as shown in Table 1. It is reasonable to assume that membranes with different lipophilicities will"require" surfactants of different HLB to achieve penetration and fluidization one of the difficulties in discerning this optimal value of HLB resides in the problems of analysis of data in the literature. For example, Hirai et al. (8 ) examined the effect of a large series of alkyl polyoxyethylene ethers (C4,C0, Cj2 and C 2 series) on the absorption of insulin through the nasal mucosa of rats. Some results are shown in Table II. 

Surfactants have been the most investigated chemicals to promote drug absorption from all body tracts. In this section, we will focus on work carried out from the early stages on the enhancing effects of surfactants on drug GI absorption as well as on their interactions with the GI membrane and their toxicity. Systems with multifactorial effects such as emulsions and microemulsions are not the focus of this review. 

In 1978, two papers, one from Israel and one from Japan, published in the same issue of the Journal of Pharmacy and Pharmacology reported successful rectal insulin absorption by use of polyoxyethylene (POE) ether nonionic surfactants [59,60], These reports led to further investigations on the use of surfactants for enhancing the absorption of macromolecules. Later in this chapter we will discuss the work done on the enteral delivery of large molecules with nonionic and anionic promoters, which have been the most investigated ones to date. 

For the last three decades, intensive research on the GI delivery of macromolecules has been conducted. Various approaches have been tested to promote the absorption of high MW drugs. One of the earliest strategies, which is still under investigation, is the use of surfactants. Surfactants have been demonstrated in numerous studies to efficiently enhance the enteral bioavailability of polypeptides, polysaccharides, and nucleotides. However, a major limiting factor in the application of these promoters is the potential toxicity of the surfactants... 

Sekine, M., et al. 1985. Improvement of bioavailability of poorly absorbed drugs. V. Effect of surfactants on the promoting effect of medium chain glyceride for the rectal absorption of (3-lactam antibiotics in rats and dogs. J Pharmacobiodyn 8 653. 

Azone (laurocapram) is used extensively as a transdermal permeation enhancer, and has also found use in buccal drug delivery. It is a lipophilic surfactant in nature (Figure 10.4). Permeation of salicylic acid was enhanced by the pre-application of an Azone emulsion in vivo in a keratinized hamster cheek pouch model [35]. Octreotide and some hydrophobic compounds absorption have also been improved by the use of Azone [36], Azone was shown to interact with the lipid domains and alter the molecular moment on the surface of the bilayers [37], In skin it has been proposed that Azone was able to form ion pairs with anionic drugs to promote their permeation [38],... 

Examines surfactant use to accelerate macromolecule input, targeted gastrointestinal delivery, and chemical means of enhancement, as well as promoted buccal and sublingual absorption... 

Interestingly, a prolonged hypoglycemic effect was also observed with insulin entrapped in poly(alkylcya-noacrylate) nanospheres when these were dispersed in an oily phase containing surfactant. " This suggests that some components of nanocapsules could act as promoters of absorption. 

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