Re: How do Antacid Tablets neutralise acid in the stomach

Our stomachs produce gastric acid to aid in digestion. This acid is mainly composed of hydrochloric acid that is secreted by cells of the stomach lining called parietal cells. Excessive secretion of this acid is common and can lead to many stomach problems such as gastritis, gastric ulcers and peptic acid disease. These disorders are treated by antacids which reduce the amount of acid in the stomach by various means.

Most antacids contain weak bases and they neutralize the stomach acids by reacting with them chemically. These antacids are best taken for occasional stomach problems and they act very rapidly to provide relief. Some of the most common bases that are used as antacids are:

• Mg(OH)₂, magnesium hydroxide, or "milk of magnesia"
• Al(OH)₃, aluminum hydroxide
• NaHCO₃, sodium bicarbonate
• CaCO₃, calcium carbonate

weak base + hydrochloric acid --> salt + water

A specific example of this chemical reaction is:

Mg(OH)₂ + 2 HCl --> MgCl₂ + 2 H₂O

There are other forms of antacid that work by less direct means. There are two types of pharmaceutical drugs that act indirectly to reduce the amount of stomach acid. They are called histamine H2 antagonists (such as Pepcid, Zantac, and Tagamet) and proton pump inhibitors (such as Prilosec and Prevacid). Both of these types drugs act to suppress the formation of stomach acids. Essentially, they turn off the biochemical machinery that produces the stomach acid. These drugs are slower acting than the bases mentioned above, but they provide relief for a much longer time. They are usually taken by people with chronic stomach problems.

Reference: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 8th edition, Pergamon Press, 1990 (pp. 897-909).