Antacids(Anti of acid) are substances, which on ingestion react with gastric acid and lower the acidity of gastric contents. They are mainly of weak bases.
They produce considerable immediate symptomatic relief in patients with duodenal Ulcer, gastritis, and Reflux esophagitis of various pains associated with hyper acidity.It is :
1. Antagonist against an acid-by neutralizing the gastric- acid as an antacid.
2. Antagonist against some gastro intestinal disorders like-Gastritis, Peptic Ulcer, Duodenal Ulcer etc. Antacid acts as an antagonist by giving relief from these disorders.
3. Antagonist against some physiological activities, i.e. Antacids show some side effects like Hypercalcemia, Constipation,Hyperphosphatemia, Milk alkali Syndrome, Renal insufficiency, Systemic alkalosis, etc. which are produced due to the ingestion of antacids. So, here antacid itself an antagonist against normal physiological activities.
Types of Antacids: They are mainly classified according to their rapid on set of action and with their absorption capacity. They are of two types such as-
A) Systemic antacids
B) Non systemic antacids
Systemic antacids:
They are soluble, readily absorbed and capable of changing the pH of extracellular fluid. Above all, the main criteria of these type of antacids is they produce Systemic alkalosis.Example: Sodium bi-carbonate. (NaHCO3)
Sodium bi-carbonate(NaHCO3) : which is known as backing soda most available product that is used as an antacid having a rapid on set of action by neutralizing the gastric acid. It causes a sharp increase of gastric pH up to or above pH-7
NaHCO3 + HCI -> NaCI + H2O + CO2
Adverse Reactions:
1. The release of CO2 with resultant belching of flatulence causes gastric distention, posing a risk to people who have gastric ulcers approaching the
perforation stage.
2. Systemic alkalosis may also occur.
Non systemic antacids: They form insoluble compounds. They have poor absorption capacity. They don’t produce any systemic effects. Examples:
1. Magnesium hydroxide [Mg(OH]2
2. Aluminium hydroxide [A1(OH)3
3. Calcium Carbonate [CaCO3]
4. Combined Antacids.
Calcium Carbonate : CaCO3
The calcium containing preparations: Specially of CaCO3 are considered by some to be the antacids of choice. They have rapid action (1 gm, neutralizes 21 meq, of acid) of largely nonsystemic.
CaCO3 + 2HCI -> CaCI2 + H2O + CO2
Adverse effects:
1. It has a tendency to produce constipation which may be reduced in combination with magnesium antacid.
2. The most serious side effect is Milk alkali syndrome. This can occur during prolonged administration of large doses of CaCO3 together
with large amounts of milk.
3. The other effects are Renal insufficiency, Hypercalcemia, Hyperphospatemia and Azotemia.
4. Aluminum containing antacids:
They are widely used. They are nonsystemic and also called "Buffer antacids" as they don’t raise the gastric pH above 4.5.
They are found in two dosages from as,
1. Aluminum hydroxide Gel
2. Dried Aluminum hydroxide Gel.
First one is in suspension form and 2nd one is in tablet form. Both of them are popular antacids but the gel has more rapid onset of action than the dried gel.
Adverse effects :
1. Because of forming the water soluble astringent salt, A1C1,, they may produce constipation and occasionally nausea and vomiting.
2. It may create Hypophosphatemia by reducing the phosphate in the intestinal tract. To overcome the constipation it sometimes used in combination with Magnesium antacids.
Magnesium containing Antacids:
There are a large number of officials magnesium containing antacids. They are :
1. Magnesium Carbonate
2. Magnesium Hydroxide
3. Magnesium Oxide
4. Magnesium Trisilicate
With the possible exception of Magnesium Trisilicate they all function in the same manner. Among them magnesium Hydroxide available as Milk of Magnesia in the market is one of the best well-known magnesium containing antacid. It is also used as laxative.
Adverse effects :
1. It has a mild cathartic effect
2. Although a small amount of magnesium antacids are absorbed into the blood, it produces toxicity only in the presence of impaired renal function. The toxicity is characterized by central nervous system depression.
3.Combination antacid preparations:
Because no single antacid meets all the criteria for an ideal antacid, several products are on the market containing mixtures of antacids. Most of the combination products are an attempt to use one component to antagonize one or more side effects of another component, e. g. to balance the constipate effect of Calcium and Aluminum, the laxative effect of Magnesium is mixed. Some of the products are also a mixture of an antacid with rapid on set of action & one with a supposedly longer duration of action.
The combined antacids are now the most acceptable antacid containing preparations, than that of individual ones. Some of the combined antacid preparations are described below :
Aluminum Hydroxide gel-Magnesium Hydroxide preparations:
This is available in suspension & tablet dosages forms. Example:
1. Alumina & Magnesium Oral suspension. U.S.P. XVIII contains 4% aluminum Oxide & 2% Magnesium Hydroxide.
2. Aluminum Hydroxide Gel Magnesium Trisillicate combinations.
3. Magaldrate N.F. XIII contains the equivalent of 28-39% Magnesium oxide (MgO) of 17-25% of Aluminum oxide (AL2O3)
4. Calcium Carbonate Aluminum Hydroxide Gel- combinations.
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