Unit III Antacid (Gastrointestinal Agent) Pharmaceutical Inorganic chemistry

  

 

• Antacid are the agent that are used to counteract excess acidity .These are the drugs treat with gastric HCl and lower the acidity.

Classification of Antacid:

• Systemic antacids(absorbable): sodium bicarbonate
• Non-systemic antacids(non-absorbable): this is furthers classified into tour types

            a)Aluminum containing antacids- Aluminum Hydroxide

            b)Calcium containing antacids-Calcium carbonate

            c) Magnesium containing antacids- magnesium carbonate

             d)combination antacids preparation -Aluminum hydroxide gel

  Ideal properties of Antacid:

•  1Antacids should have rapid onset of action and  should exert their effect for a long period of time
• They should inhibit pepsin 
• Antacid should not got absorbed and cause systemic  alkalosis
• They should have a buffering capacity in pH range of 4-6
• They should be finely divided and insoluble in water
• They should not cause any side effect .
• They should not interfere with the absorption of food.
•  They should not cause rebound hyperacidity
• They should be palatable and impressive
• They should be stable and readily available

Combinations of Antacid

Systematic antacids are not used regularly as they cause alkalosis and congestive heat failure because of sodium ion in excess Non-systematic antacids are more content and effective as compared to systematic antacids they are insoluble and poorly absorbed systematically but they have some time unfavorable side effect.

         so, each solo compound among antacids have same or other side effect when used for larger duration. To decrease the adverse effect associated with antacids, the combination of antacid.

Example

• Magnesium and Aluminum containing preparation
• calcium and magnesium containing preparation, where are having laxative effects and other have constipation
• antacid combine with simethicone or alginate type compounds, which have v  or protective action 

 Sodium bicarbonate

 Molecular formula  :         NaHCO3

 Molar mass              :         84.01 g/mol

 Synonym                  :         Baking soda; Bread soda, Cooking soda, Bicarbonate of soda

 Preparation

• NaHCO3 may be obtained by the reaction of carbon dioxide with an aqueous solution of sodium hydroxide. The initial reaction produces sodium carbonate. Further addition of carbon dioxide produces sodium bicarbonate

CO2 + 2 NaOH → Na2CO3 + H2O

Na2CO3 + CO2 + H2O → 2 NaHCO3

• On an industrial scale it is obtained by Solvay process:

CO2 + H2O → H2CO3

NH3 + H2CO3 → NH4HCO3

NaCl + NH4HCO3 → NaHCO3 + NH4Cl

 Assay

• Weigh accurately 1gm of Sodium bicarbonate and dissolve in 20 ml of water, titrate the solution with 0.5N sulphuric acid using methyl orange as indicator.
• Each ml of 0.5N sulphuric acid ≡ 0.0425gm of NaHCO3

 Uses:

• It is used as Systemic antacid and in electrolyte replacement.
•  It is used as systemic alkalinizing agent used in the treatment of metabolic acidosis (increase in acidity).
•  Bicarbonate of soda can also be useful in removing splinters from the skin.
•  Sodium bicarbonate can be added to local anesthetics, to speed up the onset of their effects and make their injection less painful.
•  Sodium bicarbonate may be used as a buffering agent, combined with table salt, when creating a solution for nasal irrigation.
•  0.1% to 1% Sodium bicarbonate solution used as eye lotion.
•  Used removed ear wax and lubricating fluid for contact lenses.
•  5% to 10% Sodium bicarbonate solution used as local applicants for burn, insect bites etc.
•  Used in preparation of effervescent formulation.

 Storage: Store in air tight container.

Aluminum hydroxide gel

 Molecular formula    :    Al(OH)3

  Molar mass    :     78.00 g/mol

 Synonym    :    Hydrated alumina, Ortho Aluminic acid, Aluminic acid

Preparation

- It is prepared by hot solution of potash alum slowly with constant stirring to a hot solution of sodium carbonate.

 Uses

•  Aluminum salts remain in the stomach for long periods and slowly react with stomach acid to form aluminum chloride. Aluminum hydroxide may inhibit the action of pepsin and stimulate stomach mucus secretion.
• Aluminium hydroxide used as gastric antacid.
•  Aluminium hydroxide used in treatment of Gastro esophageal reflux disorder.
•  ULCER PROTECTIVES: Basic aluminium hydroxide of sulfated sucrose is known as Sucralfate, which is used as protective Sucralfate is minimally absorbed after oral administration; action is entirely local. It promotes healing of both duodenal and gastric ulcers. (Sucralfate must be taken before meals)
•  In treatment of Zollinger-Ellison Syndrome

Magnesium hydroxide

 Molecular formula    :    Mg(OH)2

  Molar mass    :     58.31 g/mol

• Mg2+ Salts or Oxide or Hydroxide acts as both antacids and laxative agents.

 Preparation

•  Combining a solution of many magnesium salts with basic water induces precipitation of solid Mg(OH)2:

Mg2+ + 2 OH− → Mg(OH)2

• On a commercial scale, Mg(OH)2 is produced by treating seawater with lime [Ca(OH)2].

Mg2+ + Ca(OH)2 → Mg(OH)2 + Ca2+

• Laboratory Preparation: MgCO3 + 2 NaOH → Mg(OH)2 + Na2CO3

 Uses

•  Used as weak antacid and laxative.
•  Most commonly used antacids combine aluminum hydroxide and magnesium hydroxide. The combination decreases the adverse effects of diarrhea (with magnesium products) and constipation (with aluminum products). Calcium carbonate is effective in relieving heartburn, but it is infrequently used to treat peptic ulcers or GERD.