What is the function of Antacids ? These are drugs which are usually alkaline substances Used for neutralizing excess acid in the stomach Helps patients suffering from Hyperacidity

Classification of Antacids Systemic antacids : These are soluble, readily absorbable readily absorbable and capable of producing systemic electrolytic alterations and alkalosis. eg. NaHCO3 Non-Systemic antacids : These are not absorbed to a significant extent and thus do not exert an appreciable systemic effect. eg. Al(OH)3, CaCO3 etc.

Different Classes of Non-systemic antacids Aluminium containing antacids: Aluminium hydroxide, Aluminium phosphate, Dihydroxyaluminium sodium carbonate, Basic Aluminium carbonate (gel) etc. Calcium containing antacids: Calcium carbonate, tribasic calcium phosphate. Magnesium containing antacids: Magnesium carbonate, Magnesium carbonate, Magnesium hydroxide, Magnesium oxide, Magnesium phosphate, Magnesium trisilicate.

Requirements for an ideal antacid It should be insoluble in water and has fine particle form. It should not be absorbable or cause systemic alkalosis. It should be able to exert its effect gradually and over a long period of time. It should not be a laxative or cause constipation. It should not cause any side effects. It should be stable and readily available. The reaction between antacid and gastric hydrochloric acid should not produce large volume of gases.

Preparations containing combinations of antacids Many preparations which are having combination of antacids are being marketed and such combination is to counteract the constipative action of the aluminium and calcium containing antacids with laxative effect of magnesium containing antacids. Combinations of antacids may have one rapidly acting antacid which is combined with an antacid with longer duration of action. Antacids may be combined with simethicone type of compounds which are having antiflatulant action.

Combination preparations Aluminium hydroxide-Magnesium carbonate co-dried gel : Co-precipitate of Al(OH)3 and MgCO3 and contain critical proportion of water for antacid activity. Algicon tablets: Prepared by Al(OH)3-MgCO3 co-dried gel, Magnesium alginate, Magnesium carbonate, Potassium bicarbonate. Simeco gels: Contain Al(OH)3-MgCO3 co-dried gel, Mg(OH)2 and activated dimethjicone. Aluminium hydroxide gel-Magnesium trisilicate combinations-Laxative, constipative and protective effect. Magaldrate: Combination of Al(OH)3 and Mg(OH)2. CaCO3 with Al(OH)3 gel yield rapidly acting product with prolonged action. Algenic acid and Sodium bicarbonate containing antacid mixtures.

Sodium Bicarbonate It is commonly known as Baking soda having the chemical formula NaHCO3. Preparation: In small scale preparation it is prepared by passing CO2 gas through a solution of Sodium hydroxide. The solution is concentrated to get the product. 2NaOH + CO2  Na2CO3 + H2O Na2CO3 + H2O + CO2  2NaHCO3

Industrial scale preparation of Sodium bicarbonate Brine solution is saturated with ammonia to remove traces of impurities like Mg and Fe. Solution is filtered and passed through the carbonating tower. Come in contact with a current of CO2 and the tower is cooled to enhance precipitation. The precipitate is filtered out and dried.

Properties of Sodium bicarbonate It occurs in white crystalline or amorphous powder having a saline test. Freely soluble in water but practically insoluble in alcohol. On heating (at 100 C) it gets converted into Sesquicarbonate (Na2CO3, NaHCO3, 2H2O). Gives an effervescence with acids. Its solution is alkaline in water.

Assay 1 gm weighed accurately Dissolved in 20ml of water. Titrated with o.5 N H2SO4 (using methyl orange as indicator). Each ml of 0.5 N H2SO4 ≡ gm 0f NaHCO3

Usage and Storage In medicine it is mainly used for its neutralizing properties. Used as an antacid and to combat with systemic acidosis. Aqueous solutions are used as local applicants for burns, insect bites etc. Sodium bicarbonate always should be stored in a tight closed container.

Aluminum Hydroxide gel It is an aqueous white viscous suspension of hydrated aluminum oxide having varying amounts of basic aluminum carbonate. The preparation contains not less than 3.5 per cent and not more than 4.4 per cent w/w of aluminum oxide (Al2O3).

Preparation Prepared by adding a hot solution of potash alum with constant stirring to a hot solution of sodium carbonate. 3Na2CO3 + 2KAl(SO4)2 + 3H2O  3Na2SO4 + K2SO4 + 2Al(OH) + 3CO2 After complete removal of CO2 the precipitated aluminum hydroxide is filtered. To make it free from the sulphate ion it is thoroughly washed with hot water.

Properties Aluminum hydroxide gel is a white viscous suspension. It gives astringent aluminum chloride when it reacts with gastric hydrochloric acid. This results into constipation. Al(OH)3 + 3HCl  AlCl3 + 3H2O

Milk of Magnesia It is a suspension having not less than 7 per cent w/w and not more than 8.5 per cent w/w of magnesium hyddroxide [Mg(OH)2] in purified water. Milk of magnesia is usually dispersed in blue colored bottles to enhance whiteness. It is white, uniform suspension and used as an antacid and laxative. Used as the alkaline mouthwash and because of alkalinity it can cause liberation of alkaloids from their solution.

Preparation of magnesium hydroxide gel Light magnesium oxide is mixed with solution of sodium hydroxide to get a smooth cream. Now it is diluted with water and the suspension is poured in thin stream into a solution of magnesium sulphate. The precipitate is allowed to settle and upper liquid is removed by decantation. The residue is washed with water until it becomes free from sulphate ion. Residue is mixed with water to get the required volume.

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