Roughly 95 million Americans suffer from heartburn, which can result from stress, eating too much or too fast, or eating spicy or fatty foods. Symptoms include a burning sensation, gas, nausea, and pain. Many people treat this condition by using antacids, an over-the-counter (OTC) drug taken orally that comes in liquid or tablet form. Typical well-known brands include Tums, Rolaids, and Alka-Seltzer. Mylanta is one brand that comes in liquid form. Brands like Alka-Seltzer are taken in suspension form. Tablets consist of fine antacid powder combined with flavorings and binders. Simethicone is often added to antacids as an anti-gas agent.
The antacid market covers a wide range of products. In the United States alone there are over 120 different formulations, composed of single ingredients or mixtures. In 1997, traditional antacids (acid neutralizers) generated sales of $770 million in the United States, out of the antacid-antigas market totaling $1.32 billion. The rest of the market goes to acid blockers, which prevent the action of histamine on the acid-secreting cells of the stomach, reducing acid secretion. Commercial OTC brands include Tagamet and Zantac, which use cimetidine and ranitidine, respectively, as the blocking agents.
Antacids based on calcium carbonate have been used for over 2,000 years. This material occurs naturally in coral and limestone and is still used in products such as Tums. However, it wasn't until the nineteenth century that scientists gained a better understanding of the digestive processes of the stomach. A bizarre incident led to the discovery that the stomach produces hydrochloric acid. In 1822, a man accidentally shot himself in the stomach while cleaning his shotgun. The wound never properly healed, leaving a hole in the stomach covered by a flap of skin. As a result, the contents of the stomach could be observed, including the excretion of gastric juices. These were removed and analyzed and were found to contain hydrochloric acid (HCl).
Over the last century, antacids were developed based on the hydroxides and carbonates of the group II and III metals, as well as the bicarbonates of the alkali metals. All currently marketed antacids contain at least one of the following metals: aluminum, calcium, magnesium, sodium, potassium, or bismuth. Antacids help neutralize excess acid produced in the stomach, i.e. the hydrogenionconcentration is reduced. The effectiveness of antacids is determined by its rate of reaction and residence time, which in turn are affected by various factors. Since metal-containing antacids can interfere with the absorption of many prescribed medications, especially antibiotics, non-metal antacids also have been developed.
Antacids alone or in combination with simethicone may also be used to treat the symptoms of stomach or duodenal ulcers. With larger doses than those used for the antacid effect, magnesium hydroxide (magnesia) and magnesium oxide antacids produce a laxative effect. Some antacids, like aluminum carbonate and aluminum hydroxide may be prescribed with a low-phosphate diet to treat hyperphosphatemia (too much phosphate in the blood). Aluminum carbonate and aluminum hydroxide may also be used with a low-phosphate diet to prevent the formation of some kinds of kidney stones.
The action of antacids is based on neutralization, the chemical process in which an acid and a base react to form a salt and water. For example, when an acid reacts with a hydroxide, a salt and water are produced as in the following equation: HCl (aq) + NaOH (aq) NaCl (aq) + H20. (Hydrochloric acid reacts with sodium hydroxide to produce salt and water.)
In the case of sodium bicarbonate, or baking soda (NaHCO3), a rapid reaction occurs with gastic acid to produce an increase in gastic pH.Sodium chloride, carbon dioxide gas, and water are formed during this reaction. One gram of sodium bicarbonate will neutralize 11.9 mEq of acid. However, too large a dose can lead to the production of alkaline urine, resulting in kidney problems. Since neutralization is due to the bicarbonate, other soluble bicarbonates (potassium bicarbonate) can be used as bicarbonates.
Calcium carbonate (CaCO3) and other calcium compounds are used either alone or with magnesium compounds. With calcium carbonate, neutralization of acid involves the formation of calcium chloride, carbon dioxide, and water. One gram of this antacid will neutralize 20 mEq of acid. Negative side effects include constipation and acid rebound.
Magnesium compounds include magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), and magnesium carbonate (MgCO3-Mg(OH) 2- 3H2O. In the presence of water, magnesium oxide is converted to the hydroxide. The latter reacts with gastric acid to produce magnesium chloride and water. The commercial antacid made with this ingredient is commonly known as milk of magnesia, which contains 7-8.5% of the compound. One gram of magnesium hydroxide neutralizes 32.6 mEq of gastric acid and one ml of milk of magnesia will neutralize approximately 2.7 mEq of acid.
Magnesium compounds have the advantage of producing little absorption, having a prolonged action, and generating no carbon dioxide (except for magnesium carbonate). However, the magnesium chloride that is produced acts as a laxative; therefore, most commercial formulations also contain calcium carbonate or aluminum hydroxide to prevent this problem.
Aluminum compounds include aluminum hydroxide (Al(OH) 3), aluminum carbonate (Al2O3- CO2), and aluminum glycinate, which contains aluminum oxide (Al2O3) and an acid called glycine. The commercial version of aluminum hydroxide usually consists of an aqueous suspension containing a small amount of aluminum oxide. During neutralization, aluminum hydroxide forms aluminum chloride and water; each milliliter of the suspension neutralizes from 0.4-1.8 mEq acid in 30 minutes. However, if the pH goes above 5, the neutralization reaction is likely to be incomplete. Though aluminum hydroxide has a long shelf life it can cause constipation so is often used in combination with magnesium antacids. Aluminum carbonate has similar antacid properties to aluminum hydroxide.
The demand for antacids is expected to grow as the number of people suffering from heartburn increases due to an aging population, more stressful lifestyles, and eating out more often. Acid blockers may continue to increase in popularity at the expense of acid neutralizers. Drug manufacturers of both types will continue to improve their antacid products regarding taste, cost, and effectiveness to make it even easier for the consumer to treat themselves.
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