Absorption, generally

The first synthetic polyglycoHc acid suture was introduced in 1970 with great success (21). This is because synthetic polymers are preferable to natural polymers since greater control over uniformity and mechanical properties are obtainable. The foreign body response to synthetic polymer absorption generally is quite predictable whereas catgut absorption is variable and usually produces a more intense inflammatory reaction (22). This greater tissue compatibihty is cmcial when the implant must serve as an inert, mechanical device prior to bioresorption. 

Absorbent Flow Failure - For lean oil absorption generally, no relief requirement results from lean oil failure. However, in a unit where large quantities of inlet vapor may be removed in the absorber, loss of absorbent could cause a pressure rise to relief pressure, since the downstream system may not be adequate to handle the increased flow. In such cases, the effect of this additional vapor flow into downstream equipment must be analyzed. 

The values of r and a in Table 4-2 show that photoelectric absorption generally makes the greater contribution to the mass absorption coefficient. Absorption leading to scattering, which will be discussed in the next section, gains in relative importance as atomic number Z and wavelength X decrease. 

Equation (3) is in the form of a differential equation describing a first-order kinetic process, and, as a result, drug absorption generally adheres to first-order kinetics. The rate of absorption should increase directly with an increase in drug concentration in the GI fluids. 

The fact that the GIT is so well perfused by the bloodstream permits efficient delivery of absorbed materials to the body. As a result of this rapid blood perfusion, the blood at the site of absorption represents a virtual sink for absorbed material. Under normal conditions, then, there is never a buildup in drug concentration in the blood at the site of absorption. Therefore, the concentration gradient will favor further unidirectional transfer of drug from the gut to the blood. Usually, then, blood flow is not an important consideration in drug absorption. Generally, the properties of the dosage form (especially dissolution rate) or the compound s inherent absorbability will be the limiting factors in absorption. 

Injection, inhalation, and dermal absorption generally result in the toxicant entering the bloodstream unaltered. Toxicants entering through ingestion are frequently modified or excreted in bile. 

Even though the ranges for individual types often overlap, it may be possible to make a definite decision from information derived from other regions of the IR spectrum. Thus esters also exhibit strong C-0 stretching absorption between 1200 and 1300 cm- while carboxylic acids exhibit 0-H stretching absorption generally near 3000 cm-. ... 

Generally the smaller the molecule the more easily it will be taken up. Molecular weights below 500 are favorable for absorption molecular weights in the 1000s do not favor absorption. Generally solids have to dissolve before they can be absorbed. It is possible for small amounts of particles in the nanometer size range to be taken up by pinocytosis. The absorption of very large particles, several hundreds of micrometers in diameter, that are administered dry (e.g., in the diet) or in a suspension may be reduced because of the time taken for the particle to dissolve. This would be particularly relevant for poorly water-soluble substances. 

SYMPTOMS - Dim vision, pinpoint pupils (may not occur from skin absorption), runny nose, tightness of chest, sweating, muscular twitching nausea, vomiting, weakness and coma. Vapor inhalation or absorption of vapor through the eyes causes quickest onset of symptoms. Skin absorption generally takes about 10 minutes. 

Intramuscular and subcutaneous injections are by far the most common means of parenteral drug administration. Because of the high tissue blood flow and the ability of the injected solution to diffuse laterally, drug absorption generally is more rapid after intramuscular than after subcutaneous injection. Drug absorption from intramuscular and subcutaneous sites depends on the quantity and composition of the connective tissue, the capillary density, and the rate of vascular perfusion of the area. These factors can be influenced by the coinjection of agents that alter local blood flow (e.g., vasoconstrictors or vasodilators) or by substances that decrease tissue resistance to lateral diffusion (e.g., hyaluronidase). 

This band is unusually low in frequency for a C—H stretching vibration although the band is rather weak, it occurs in a region of the spectrum where other absorptions generally are absent so it can be identified with no special difficulty. 

But there are a number of limitations to UV detection in the analysis of additives. Detection without derivatization relies on the presence of UV-absorbing functional groups. Although these groups are quite sensitive, UV absorption generally is not highly selective. Many compounds absorb in the UV range. So with many HPLC methods, the only information provided is retention time. 

The actual spectral absorption generally observed in vision research is not the actual function for several reasons, some of which will be discussed in the next Section. However, a major reason, is related to the design of the experiment. The visual spectra of the individual chromophores of vision are relatively narrow. If an experiment is designed where the absorption spectrum is sampled using a finite width spectral filter, the measured spectrum is defined by the convolution of the actual spectral transmission function and the filter sampling function. The resulting mathematics can assume three forms. 

Here, at is the Dirac a-matrix, A(r, t) is the vector potential of the field (divA = 0), and Ho is the Hamiltonian of an isolated atom whose energy in the initial state of the reaction is denoted by Ef. H0 i) = E i). Equation (5) defines the effective two-photon operator Q(2 ui,u> ) which has the dimension of L3 and is a straightforward relativistic generalization of its nonrelativistic counterpart that has been first introduced in [28] to describe the process of two-photon absorption. Generally, the matrix elements of u>,u> ) can be expressed explicitly as... 

The n — tt transitions of carbonyl groups have small molar absorptivities, generally about 10 to 200. These absorptions are around 1000 times weaker than 77 — tt ... 

C NMR absorptions occur over a range of 250 ppm, while H NMR absorptions generally occur over a range of only 10 ppm. The spread of peaks in 13C NMR is therefore much greater, so accidental overlap is less likely. In addition, normal 13C NMR spectra are uncomplicated by spin-spin splitting, and the total number of lines is smaller. 

It should be noted that dermal absorption generally continues after cessation of actual exposure. In vivo absorption should therefore preferably be assessed by repeated and continued sampling after cessation of the exposure until the test compound and/or its metabolites are no longer detectable in excreta in two serial samples (EC, 2002) or 10 urinary excretion half-lives have passed (Thongsinthusak et al., 1999). In vitro studies may also be continued until a... 

Absorption generally depends very much on the large difference in drug concentration between the gastrointestinal tract and the blood. A knowledge of the blood flow to the different parts of the gastrointestinal tract and of the pH of its contents is therefore important. These factors, together with the surface areas available for absorption and the... 

By choosing a reactant having a suitable solubility and concentration along with an adequate rate of reaction, either the mass-transfer coefficients or the interfacial area (or both) can be deduced from the overall rate of absorption. Generally a steady flow of each phase through the reactor is assumed. 

Drug absorption generally occurs either through passive transcellular or paracellu-lar diffusion, active carrier transport, or active efflux mechanisms. Several methods have been developed to aid in the understanding of the absorption of new lead compotmds. The most common ones use an immortalized cell line (e.g., Caco-2, Madin-Darby canine kidney, and the like) to mimic the intestinal epithelium. These in vitro models provide more predictive permeability information than the artificial membrane systems (i.e., PAMPA and permeability assays, described previously) based on the cells ability to promote (active transport) or resist (efflux) transport. Various in vitro methods are listed in the U.S. FDA guidelines. These are acceptable to evaluate the permeability of a drug substance, and includes a monolayer of suitable epithelial cells, and one such epithelial cell line that has been widely used as a model system of intestinal permeability is the Caco-2 cell line. 

Equation 18.4, then, it is apparent that the fliK of drug across the intestine is directly proportional to its aqueous solubility. For drugs that have high intestinal membrane permeability aqueous solubility may be the limiting factor to adequate drug absorption. Generally, only the un-ionized species is absorbed thus, for ionizable compounds, the concentration of the un-ionized form should be considered in Equation 18.4. 

Unless specified, absorption generally includes adsorption and hydrogen generally includes protium ( H or H and H2) and deuterium ( H or D and D2). 

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