Aluminum-based antacids

Hyperphosphatemia is generally benign and rarely needs aggressive therapy. Dietary restriction of phosphate and protein is effective for most minor elevations. Phosphate binders such as aluminum-based antacids, calcium carbonate, calcium acetate (PhosLo , Nabi), sevelamer (Renagel , Genzyme), and lanthanum carbonate (Fosrenol , Shire) may be necessary for some patients.43 If patients exhibit findings of hypocalcemia (tetany), IV calcium should be administered empirically. 

There are compounds for which standard in vivo tests do not provide additional useful information. This is particularly true for compounds for which data from studies on toxicokinetics or pharmacokinetics indicate that they are not systemically absorbed and therefore are not available for the target tissues. Examples of such compounds are some radioimaging agents, aluminum based antacids, and some dermally applied pharmaceuticals. In those cases other tests, systems should be considered to be more relevant. 

Dietary phtxsphate deficiency is relatively rare because the phosphate content in plant and animal foods is well above the requirement and b ause of the efficient absorption of phosphate (50-90%). Phosphate deficiency can occur in a number of situations. It can occur with the chronic intake of aluminum-based antacids, particularly with a low-phosphate diet. These antacids form a complex with dietary phosphate, preventing its absorption and resulting in the deficiency. Deficiency can occur with increased urinary excretion of phosphate that occurs w ith starvation and in diabetics experiencing ketoacidosis. Chronic alcoholics may be phosphate deficient because of decreased dietary intake, impaired absorption, and increased urinary excretion (Berner and Shike, Phosphate defi-... 

Drugs that may affect tipranavir include aluminum- and magnesium-based antacids, azole antifungals, clarithromycin, efavirenz, loperamide, NRTIs (ie, didanosine, zidovudine), rifamycins (rifampin), St. John s wort, tenofovir. 

The usual daily intake of phosphate is between 800 and 1200 mg/day. Absorption of phosphate may be impaired by some medications (e.g., aluminum- and magnesium-based antacids that bind phosphates) or by malabsorption syndrome. Malnourishment may result in low levels of phosphate owing to decreased food intake and decreased vitamin D intake. 

A recent consensus panel recommends calcium- or magnesium-containing antacids as first-line therapies for heartburn in pregnancy.21 This recommendation was based on the added benefit of calcium and magnesium supplementation. Avoid antacids containing aluminum hydroxide owing to associations with fetal neurotoxicity.22... 

Antacids attempt to chemically neutralize stomach acids. These drugs typically contain a base such as carbonate or hydroxide combined with aluminum, magnesium, or calcium.34 The base combines with excess hydrogen ions (H+) in the stomach to increase intra-gastric pH. The basic strategy of this chemical neutralization is illustrated in Figure 27-1. 

Because acid-pepsin disease rarely occurs in the absence of gastric acid and pepsin, antacids are highly effective in its overall management. Antacids consist of a mixture of magnesium, aluminum, and calcium compounds. Their efficacy is based on their inherent ability to react with and neutralize gastric acid. Sodium bicarbonate, which may leave the stomach rapidly, can cause alkalosis and sodium retention. Calcium salts may produce hypercalcemia, which can be detrimental in patients with impaired renal function. Aluminum salts may decrease the absorption of tetracyclines and anticholinergic drugs. 

EPA requires industry to report spills of more than 5,000 pounds of aluminum sulfate. Special regulations are set for aluminum phosphide because it is a pesticide. EPA has recommended a Secondary Maximum Contaminant Level (SMCL) of 0.05 to 0.2 milligrams per liter (mg/L) for aluminum in drinking water. The SMCL is not a based on levels that will affect humans or animals. It can be based on taste, smell, or color. OSHA says that the amount of aluminum dusts that workers breathe should be not more than 15 milligrams per cubic meter (mg/m3) of air. FDA has determined that aluminum cooking utensils, aluminum foil, antiperspirants, antacids, and other aluminum products are generally safe. To learn more, see Chapter 7. 

Although antacids contain other ingredients, all antacids contain a base that counteracts stomach acid. The base is either sodium hydrogen carbonate, NaHCOs, calcium carbonate, CaCOs, aluminum hydroxide, Al(OH)c , or magnesium hydroxide, Mg(OH)2. 

Aluminum toxicity has also been linked with oral exposure as a result of Al-containing pharmaceutical products such as Al-based phosphate binders or antacid intake. As over-the-counter antacids are an important source for human Al exposure from a quantitative point of view, patient information leaflets in Europe contain warnings of possible Al toxicity. ... 

Aluminum hydroxide, magnesium hydroxide, and calcium carbonate are all used as antacids. Write the balanced equations that show how these bases react with HCl. How many moles of stomach acid (HCl) will 1.0 g of each of these anatacids neutralize ... 

Because strong bases are completely ionized, the molarity of hydroxide ion in sodium and potassium hydroxide solutions, the monohydroxy bases, is the same as the molarity of the base itself. The OH molarity in 0.10 M NaOH is 0.10 M. In the case of Ca(OH)2, a dihydroxy base, the OH molarity is exactly two times the molarity of Ca(OH)2. Not all hydroxide compounds function well as bases because of their low solubility in water. Aluminum hydroxide, Al(OH)3, and magnesium hydroxide, Mg(OH)2 can both neutralize acids (they are used in several antacids) but neither is very soluble and cannot used to prepare solutions. 

As you can see, acid-base reactions, like precipitation reactions, are metathesis (double-displacement) reactions. The molecular equation for the reaction of aluminum hydroxide, the active ingredient in some antacid tablets, with HCl, the major component of stomach acid, shows this clearly ... 

For drugs administered oraUy, impaired gastrointestinal (GI) absorption is an important consideration. For example, aluminum ions in certain antacids or ferrous ions in oral iron supplements form insoluble chelates of tetracycline antibiotics, thereby preventing their absorption. The antifungal ketoconazole is a weak base that is only soluble at acid pH. Drugs that inhibit gastric acidity, such as the proton pump inhibitors and histamine Hj receptor antagonists, impair the dissolution and absorption of ketoconazole. 

Aluminum hydroxide is an effective antacid because it is, chemically, a base. As such, it reacts with stomach acid (hydrochloric acid HC1), to reduce the symptoms of heartburn, upset stomach, acid indigestion, and gastritis, an inflammation of the stomach lining. The compound can also be used to treat peptic ulcers on a long-term basis. A peptic ulcer is an open sore in the lining of the stomach or the first part of the small intestine. 

The alkaline earth hydroxides are not very soluble and are used only when the solubility factor is not important. In fact, the low solubility of these bases can sometimes be an advantage. For example, many antacids are suspensions of metal hydroxides, such as aluminum hydroxide and magnesium hydroxide. The low solubility of these compounds prevents a large hydroxide ion concentration that would harm the tissues of the mouth, esophagus, and stomach. Yet these suspensions furnish plenty of hydroxide ion to react with the stomach acid, since the salts dissolve as this reaction proceeds. 

Antacids are bases used to neutralize the acid that causes heartburn. The most common antacid ingredients are magnesium and aluminum hydroxides, and bicarbonate or carbonate salts (Table 9.4). Baking soda (sodium bicarbonate) was used to relieve indigestion before many of the other commercial products became available. The bicarbonate ion, a basic anion of a weak acid, reacts with the hydronium ion from hydrochloric acid to form carbonic acid, which decomposes to give carbon dioxide and water. Note this is the same mechanism by which the blood buffering system neutralizes acid. 

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