Absorption acidic environment

Calcium carbonate should be taken with food to maximize absorption. Elderly patients or patients receiving proton pump inhibitors or H2-receptor antagonists may have added difficulty absorbing calcium supplements because of reduced stomach acidity. Better absorption may occur in this setting with calcium citrate because an acid environment is not needed for absorption it may be taken with or without food. 

In the stomach, carotenoids are exposed to acid environments. This can lead to carotenoid isomerization, which can change carotenoid antioxidant properties, solubility, and absorption. In humans, (3-carotene absorption is reduced when the pH of the gastric fluids is below 4.5 (Tang and others 1995). Vitamin E consumption seems to reduce carotenoid absorption in animals, presumably because vitamin E and carotenoids compete for absorption (Furr and Clark 1997). Dietary sterols, such as those in sterol-supplemented functional foods, are also known to decrease carotenoid absorption. 

PPIs are usually well tolerated. Potential adverse effects include headache, dizziness, somnolence, diarrhea, constipation, nausea, and vitamin B12 deficiency. All PPIs can decrease the absorption of drugs such as ketoco-nazole or itraconazole that require an acidic environment for absorption. Other drug interactions vary with each agent. 

Nasal Administration. A route that has gained increasing popularity of late for pharmaceutical administration in humans is the intranasal route. The reasons for this popularity are the ease of use (and, therefore, ready patient acceptance and high compliance rate), the high degree and rate of absorption of many substances (reportedly for most substances up to 1000 molecular weight McMartin et al., 1987), and the avoidance of the highly acid environment in the stomach and first-pass metabolism in the liver (particularly important for some of the newer peptide moieties) (Attman and Dittmer, 1971). The only special safety concerns are the potential for irritation of the mucous membrane and the rapid distribution of administered materials to the CNS. 

Absorption. Absorption of cyanide across the gastrointestinal mucosa depends on the pH of the gut and the pKa and lipid solubility of the particular cyanide compound. Hydrogen cyanide is a weak acid with a pKa of 9.2 at 25 °C. The acidic environment in the stomach favors the non-ionized form of hydrogen cyanide and facilitates absorption. Information regarding the rapid lethal effects following oral intake of cyanide in humans (Gosselin et al. 1976) indicates that cyanide is rapidly absorbed from the gastrointestinal tract. 

Absorption of phenol occurs fairly rapidly via the inhalation (Hughes and Hall 1995 Ohtsuji and Ikeda 1972 Piotrowski 1971), oral (Capel et al. 1972 Edwards et al. 1986 French et al. 1974 Hughes and Hall 1995 Kao et al. 1979 Kenyon et al. 1995), and dermal (Baranowska-Dutkiewicz 1981 Hughes and Hall 1995 Piotrowski 1971) routes. Because it is an irritant, tissue damage, inflammation, or other irritation effects may occur at the sites of absorption. Because of its high pKa, ionization will not occur within the acid environment of the gut. The action of gut microflora on phenol breakdown is not expected to be significant. 

Nicotine is distilled from bnming tobacco and carried proximally on tar droplets (also called particnlate matter), which are inhaled. Absorption of nicotine across biological membranes depends on pH. Nicotine is a weak base with a p fa of 8.0. In its ionized state, snch as in acidic environments, nicotine does not rapidly cross membranes. The pH of smoke from fine-cured tobaccos, found in most cigarettes. 

The main fluorescent pH indicator probes are based on fluorescein and therefore it is important to understand the pH-dependent ionic equilibria of it and its derivatives, hi aqueous solutions above pH 9 the phenolic and carboxylic acid functional groups in the molecule are almost totally ionised (Figure 3.14). Upon acidification of the dianion, firstly, protonation of the phenolic group occurs (pK 6.4) to yield the monoanion followed by the carboxylic acid (pA < 5), giving the neutral species of fluorescein. On further acidification the fluorescein cation pK 2.1) is generated. In strongly acidic environments fluorescein is non-fluorescent, only the mono-anion and di-anions are fluorescent, with quantum yields of 0.37 and 0.93, respectively. The pH-dependent absorption spectrum of fluorescein exhibits a blue-shift and... 

When ionic fluoride enters the acidic environment of the stomach lumen, it is largely converted to weak acid hydrogen fluoride (HF) with a pKg of 3.45 [17], The higher acidity of the stomach speeds up the process of absorption by passive diffusion from both the stomach and the small intestine, suggesting that fluoride is absorbed from the stomach as undissociated hydrogen fluoride rather than as fluoride ion [63,72]. Most of the fluoride that is not absorbed from the stomach will be rapidly absorbed from the small intestine. There is no convincing evidence that active transport processes are involved [17]. 

Gastric acidity will also affect the absorption of medication. An acidic environment increases the absorption of weak acids, whereas the absorption of weak bases is facilitated by a less acidic environment. Many psychotropic agents such as tricyclic antidepressants (TCAs] and benzodiazepines are weak bases. Older studies of gastric acid secretion found that women have approximately 33%-40% lower basal gastric acid secretion than do men [Yonkers and Hamilton 1995]. Gastric acid secretion may be further decreased in the luteal phase of the menstrual cycle (Booth et al. 1957]. 

Lower acidic environment increases absorption of weak bases (e.g., TCAs, BZDs, some antipsychotics). 

Indinavir requires an acidic environment for optimum solubility and therefore must be consumed on an empty stomach or with a small, low-fat, low-protein meal for maximal absorption (60-65%). The serum half-life is 1.5-2 hours, protein binding is approximately 60%, and the drug has a high level of cerebrospinal fluid penetration (up to 76% of serum levels). Excretion is primarily fecal. An increase in AUC by 60% and in half-life to 2.8 hours in the setting of hepatic insufficiency necessitates dose reduction. 

As important as this pH effect is, it can be subordinated by other factors. For example, as indicated earlier, the absorptive area that a drug is exposed to can be a predominating factor. In this context, even though the acidic environment of the stomach favors the absorption of weak acids (e.g., acetylsalicylic acid), aspirin is still absorbed to a greater extent, in totality, in the small intestine. A partial list of the pH of several body compartments is shown in Table 2.4. The fact that there are some variations suggests that the disposition of some drugs may be differentially affected. 

Coaxial (or assimilation) traps utilize an adsorbing material drawn out to a fine fiber to provide as much surface area as possible. The various different materials available provide varying capabilities. For example, copper provides the best absorption capabilities (particularly to hydrocarbon oils), but is not very durable and needs to be replaced often. Stainless steel (particularly good for acid environments) and bronze will survive better in tougher environments, and activated alumina is great when organics or pump oils need to be trapped. Like molecular sieves, these traps work at room temperature. Unlike molecular sieves, not all can be baked out for regeneration and typically must be replaced with the old one discarded in an environmentally safe manner because it is likely to contain a variety of harmful materials. 

Absorption Most of the penicillins are incompletely absorbed after oral administration and reach the intestine in sufficient amounts to affect the composition of the intestinal flora. However, amoxicillin is almost completely absorbed. Consequently, it is not appropriate therapy for the treatment of shigella- or salmonella-derived enteritis, since therapeutically effective levels do not reach the organisms in the intestinal crypts. Absorption of penicillin G and all the penicillinase-resistant penicillins is decreased by food in the stomach since gastric emptying time is reduced and the drugs are destroyed in the acidic environment. Therefore, they must be administered 30-60 minutes before meals or 2-3 hours postprandially. Other penicillins are less affected by food. 

The absorption of many orally administered drugs containing carboxylic acids depends on their p/Ca values. Aspirin, for example, is largely absorbed from the acidic environment of the stomach because it is present as the acid, which readily passes through the membranes into the blood. 

Q1 The stomach acts as a temporary reservoir for food and as a mixing chamber, allowing small amounts of gastric contents (chyme) to enter the duodenum at intervals. The acid environment and mechanical activity in the stomach starts the breakdown of food items and the acidity of the stomach eliminates many infectious organisms present in ingested material. Finally, an important function is the production and secretion of intrinsic factor, a compound that is necessary for effective absorption of vitamin Bi2 from the diet. 

DIPYRIDAMOLE ANTACIDS Possible l bioavailability of dipyridamole Dipyridamole tablets require an acidic environment for adequate dissolution t in pH of the stomach impairs dissolution and therefore may 1 absorption of the drug t the dose of dipyridamole or consider using an alternative antiplatelet drug... 

AZOLES ANTACIDS i plasma concentration of itraconazole and ketoconazole, with risk of therapeutic failure Itraconazole absorption in capsule form requires an acidic gastric environment and thus absorption would l Separate administration of agents that i gastric acidity by 1-2 hours. However, absorption of itraconazole liquid solution does not require an acidic environment and could be used instead it does not need to be given with food. Fluconazole absorption is not pH dependent, and this is a suitable alternative... 

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