ANTACIDS


Background:

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The gastro-intestinal tract must generate and maintain certain pH environments as a means of controlling the activity of digestive enzymes. Gastric juices that contain hydrochloric acid are secreted from the gastric glands, which are located on the lining of the human stomach. Gastric juices tend to have a very acidic pH ranging from 1.0 to 3.0. The purpose of the very acidic solution is to suppress growth of harmful bacteria and to help create the optimum environment for digestive enzymes. Overproduction of gastric juices can be caused by over-eating, stress, alcohol, smoking, and some anti-inflammatory drugs, which in turn can cause the following issues: indigestion (feeling of discomfort caused by the excess acidity) , heartburn (acid rising from the stomach into the esophagus), and ulcers (caused by the corrosion of the protective mucus layer that lines the stomach which in turn results in loss of tissue and inflammation).

What Are Antacids and How Do They Work?


An antacid is a remedy for excess stomach acidity. They are weak bases, usually, metal oxides, hydroxides, carbonates or bicarbonates that work to neutralize excess acid in the stomach to regulate and adjust the stomach pH. They buffer the stomach's gastric juices because they are basic. Antacids work by neutralizing the hydrochloric acid (in the gastric juices) to produce a salt and water, and by doing so they alleviate the symptoms that come with indigestion and also allow for reparation to the stomach lining. While most produce just a salt and water, some antacids contain metal carbonates and hydrogencarbonates which reach with the acid to produce a salt, water, and carbon dioxide. Antacids also work by inhibiting the activity of pepsin (digestive enzyme that breaks down protein into polypeptides) in the stomach.

Action of Antacids:

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1) Magnesium Oxide:
  • MgO (s) + 2HCl (aq) >> MgCl2 (aq) + H2O (l)
2) Magnesium Hydroxide:
  • Mg(OH)2 (aq) + 2HCl (aq) >> MgCl2 (aq) + H2O (l)
3) Aluminum Hydroxide:
  • Al(OH)3 (aq) + 3HCl (aq) >> AlCl3 (aq) + 3H2O (l)
4) Calcium Carbonate:
  • CaCO3 (s) + 2HCl (aq) >> CaCl2 (aq) + H2O (l) + CO2 (g)
5) Sodium Hydrogen Carbonate:
  • NaHCO3 (aq) + HCl (aq) >> NaCl (aq) H2O (l) + CO2 (g)
6) Magnesium Trisilicate:
  • Mg2Si3O8 (s) + 4HCl (aq) >> 3SiO2 (s) + 2H2O (l) + 2MgCl2 (aq)

Note: Magnesium salts tend to act faster, while aluminum compounds tend to act slower because they dissolve more slowly, but as a result aluminum compounds tend to provide longer-lasting relief.

Over-The-Counter Examples of Antacids:

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Tums
CaCO3, MgCO3, MgSi3O8
Rotaids
AlNa(OH)2CO3
Maalox
Mg(OH)2, Al(OH)3
Alka Seltzer
NaHCO3
Milk of Magnesia
Mg(OH)2
Amphogel
Al(OH)3
Di-Gel
CaCO3

Antacids and Other Chemicals:


Antacids are often combined with other chemicals to facilitate acid neutralization. They are sometimes combined with chemicals called alginates because together they produce a neutralizing layer that helps prevent acid in the stomach from rising into the esophagus, thus preventing heartburn. Alginates work by floating to the top of the stomach, which in turn helps act as a barrier for rising acid. Chemicals known as anti-foaming agents (i.e. dimethicone) are added to reduce the surface tension of gas bubbles creating a defoaming action in the stomach, which in turn helps prevent bloating of the stomach and flatulence.

Side Effects of Antacids:


Neutralizing the body's pH with antacids can prove beneficial for a short period of time, but antacids should not be taken for a long period of time. The reason for this is that antacids can lead to mal-absorption of nutrients that are vital for a healthy body. Low stomach acid inhibits the body's ability to absorb calcium (a vital component for bone health), which can lead to diseases such as osteoporosis, also mal-absorption of vitamin B12 has been linked to impaired nerve and brain function. Low stomaFch acid can also lead to mal-absorption of other vital nutrients, such as; vitamin A, vitamin B, vitamin B1, vitamin B6, folic acid, iron, magnesium, selenium, and zinc. Long term use of antacids can lead to the body producing more gastrin (a hormone that signals for the increase of acid production), which has been linked to the growth of esophageal, pancreatic, and gastric cancer cells. Antacids can also weaken the anti-microbial action of stomach acid, which functions to kill harmful bacteria and fungi in the stomach, thus leaving the body susceptible to bacterial and fungal infections.
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Aluminum Based:

Bone pain
Constipation
Discomfort
Appetite Loss
Mood Changes
Muscle Weakness
Swelling of Extremities
Weight Loss
Note: Aluminum ions can prevent uptake of phosphate ions because of the precipitation of aluminum phosphate.

Calcium Based:

Constipation
Difficulty Urinating
Frequent Urge to Urinate
Headache
Appetite Loss
Mood Changes
Muscle Pain
Nausea/Vomiting
Anxiety
Slow Breathing
Unpleasant Taste
Fatigue
Note: Excessive calcium levels caused by long term use of calcium based antacids has been linked to alkalosis, hypercalcemia, kidney stones, milk-alkali syndrome, and renal failure.

Magnesium Based:

Difficulty Urinating
Dizziness
Discomfort
Irregular Heartbeat
Appetite Loss
Mood Changes
Muscle Weakness
Fatigue
Weight Loss

Note: Magnesium hydroxide has laxative properties.

Sodium Based:

Urge to Urinate
Headache
Appetite Loss
Muscle Pain
Nausea/Vomiting
Anxiety
Slow Breathing
Swelling of Extremities
Unpleasant Taste
Fatigue
Chalky Taste
Constipation
Diarrhea
Persistent Thirst
Stool Discoloration
Stomach Cramps
Note: Sodium ions may lead to hypertension.

Antacids can have increased side effects if used in combination with other drugs because one drug can alter or amplify the effects of the other.

References:


http://www.humantouchofchemistry.com/node/226
http://www.rxlist.com/script/main/art.asp?articlekey=95545&page=3
http://refluxdefense.com/heartburn_GERD_articles/side-effects-antacids-and-acid-blockers.html
Chemistry, 3rd Edition by John Green and Sadru Damji
IB Chemistry Study Guide by Geoffrey Neuss
Pearson Baccalaureate Higher Level Chemistry

Images:

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