Question

Why are cimetidine and ranitidine better antacids than sodium hydrogen carbonate or magnesium or aluminium hydroxide?

Answer 1

To answer this question, you must recall various types of antacids and their effects on the body. An antacid is a substance that neutralizes excess acid produced in the stomach and raises the pH of the stomach to a suitable level. Generally weak bases are used as antacids.

Complete step by step solution
Sodium bicarbonate, magnesium hydroxide, aluminium hydroxide and aluminium phosphate are some common examples of basic salts used as antacids. The use of these antacids controls only the symptoms of acidity but not the causes.
Since we know that too much excess of the acid in the stomach can be life threatening in severe cases and thus, the treatment must involve the removal of the affected part of the stomach that causes the problem. It is known that histamine in the body stimulates the secretion of hydrochloric acid and pepsin in the stomach. The drugs cimetidine and ranitidine are designed in such a way that they prevent the interaction between histamine and the receptors in the wall of the stomach. Thus, less hydrochloric acid is produced and acidity is controlled. As a result, these drugs are preferred as antacids over sodium bicarbonate, magnesium hydroxide and aluminium hydroxide.

Note
The overproduction of hydrochloric acid in the stomach leads to acidity which then causes pain and irritation. When overproduced in severe amounts, it leads to the formation of ulcers in the stomach. Thus, it is essential to neutralize the excess acid produced in the stomach and for this we use weak bases. These weak bases are known as antacids as they neutralize the excess acid.