Antacids are alkaline substances (weak bases) that neutralize gastric acid (hydrochloric acid)
They react with hydrochloric acid in the stomach to produce neutral or less acidic or poorly absorbed salts and raise the PH of stomach secretion, and above PH of 4, pepsin is inactive. Antacids are divided into systemic and nonsystemic
Systemic, e.g. sodium bicarbonate are absorbed into body fluids and may alter acid – base balance. It can be used in the treatment of metabolic acidosis.
Non systemic, do not alter acid – base balance significantly. They are used as gastric antacids; and include aluminium, magnesium and calcium compounds e.g. (Al(OH)3, MgS2O3 , Mg(OH)2, CaCO3)
- Gastric antacids differ in their potency, in onset of action, duration of action and adverse effects produced.
- Magnesium compounds have a relatively high neutralizing capacity, rapid onset of action, cause diarrhoea and hypermagnesemia.
- Aluminium compounds generally have a low neutralizing capacity, slow onset of action but long duration of action and may cause constipation.
Calcium compounds are effective and have a rapid onset of action but may cause hypersecretion of acid (acid – rebound) and milk-alkali syndrome (hence rarely used in peptic ulcer disease). All gastric antacids act chemically although some like magnesium trisiolicate can also act physically.
The most commonly used antacids, are mixtures of aluminium hydroxide and magnesium hydroxide (e.g. Gelusil, Maalox etc).
Antacids act primarily in the stomach and are used to prevent and treat peptic ulcer. They are also used in the treatment of Reflux esophagitis and Gastritis
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