The antacids generally available over the counter are mainly magnesium hydroxide, magnesium trisilicate and aluminium hydroxide.

Magnesium Hydroxide: In the stomach it reacts with the acid hydrochloric acid to form magnesium chloride. There is a risk of alkalosis when taking alkaline substances in high doses but in the case of magnesium, there is no risk because magnesium ions are not easily absorbed by the gut.

Magnesium Trisilicate: This is a powder that does not dissolve in water. It reacts in the stomach with the acid to form magnesium chloride and colloidal silica. This prolongs the antacid effect and in addition it absorbs pepsin, the agent thought to be responsible for injury to the esophagus in the presence of high acid.

Aluminium Hydroxide: Reacts to hydrochloric acid in the stomach to form aluminium chloride. It can raise the pH to about 4 and also absorb pepsin. The effect is gradual and it is effective for several hours.

Sodium Bicarbonate: This is a rapidly acting antacid. It can raise the pH to 7.4. The chemical reaction between sodium bicarbonate and hydrochloric acid releases carbon dioxide. The gas builds up in the stomach and can cause belching. Carbon dioxide in the stomach is a trigger for gastrin secretion. Gastrin secretion leads to acid production and can cause a secondary wave of acid production.

High intake of sodium bicarbonate can result in alkalosis. This antacid should not be regarded as a long term acid reflux treatment because of this risk of alkalosis. It should be avoided in any one on a restricted sodium diet.

Dr. Phil Hariram,

Acid Reflux Guide.