Antacids (Pharmaceutical Inorganic Chemistry)

B.Pharm and D.Pharm PCI Syllabus, Acidity, complications of acidity, symptoms of acidity, causes of acidity, antacids, systemic antacids, non-systemic antacids, types of non-systemic antacids,calcium-containing antacids,magnesium-containing antacids, aluminum-containing antacids, combination antacids, ideal characteristics of an antacid, why combination antacids are preferred, simethicone, popular brands of antacids, sodium bicarbonate, assay of sodium bicarbonate, medicinal uses of sodium bicarbonate, aluminum hydroxide, medicinal uses of aluminum hydroxide, magnesium hydroxide mixture, milk of magnesia, medicinal uses of magnesium hydroxide.


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1. ANTACIDS Authored By: Dr. Alex Martin Ph.D , M.Pharm , FAGE

2. GASTRIC ACIDITY High amounts of HCl in stomach is referred to as Gastric Acidity SYMPTOMS Abdominal pain Burping Bloating Bad Breath Heartburn Gastric Reflux Acidic state in mouth Nausea Vomiting Decreased appetite Unexplained Weight Loss Diarrhea COMPLICATIONS Gastric Ulcer Stomach Cancer

3. COMPLICATONS Stomach Ulcer Stomach Cancer Bleeding GERD CAUSES OF HIGH ACIDITY IN STOMACH H. p yroli infection Zollinger-Elison Syndrome Gastric outlet obstruction: outlet from stomach to duodenum is blocked Abrupt abatement of H-2 Blockers Chronic Kidney Failure / Dialysis

4. ANTACIDS 1. O.T.C. Drugs that Neutralizes acidity in Stomach. 2. Therefore, it relives symptoms of acidity 3. Comfortably swallowed anytime 4. For minor symptoms MECHANISM OF ACTION OF ANTACIDS 1. Is converted into its soluble salts after being acted upon by stomach HCl . 3. Raises the pH above 4. 2. Acts as weak base, it neutralizes the gastric HCl . 4. Relives acidity and associated symptoms. 5. Suggested in Hyperchlorhydria NUETRALIZING CAPACITY OF AN ANTACID The efficiency of an antacid is determined by its neutralizing capacity. Antacids should have minimum neutralizing capacity of 5 mEq of HCl per unit dose.

5. Fine particle size. Insoluble in water. Should not cause systemic alkalosis. Should not act as laxative Should not cause constipation Should not cause any side effects Stable and readily available Should not evolve large quantities of gas on reaction with stomach HCl . Should produce a pH of 4 to 6 Gradual onset and prolonged action Should inhibit pepsin IDEAL CHARACTERISTICS OF AN ANTACID

6. TYPES OF ANTACIDS SYSTEMIC ANTACIDS Soluble in water Readily absorbed through GIT to blood to produce Systemic Alkalosis and Electrolytic alterations. Suggested in conditions of acidemia (i.e. pH of blood is below 7.35). CKD, diabetic ketoacidosis , loss of bicarbonate ions through diarrhea and vomiting. NON-SYSTEMIC ANTACIDS They produce local action by neutralizing stomach HCl . They are not absorbed into bloodstream through stomach and thus produce local action. Antacids should be taken after meals to achieve prolonged action. Eg : Sodium Bicarbonate TYPES I. Calcium Antacids II. Magnesium Antacids III. Aluminum Antacids

7. TYPES OF NON-SYSTEMIC ANTACIDS I. Calcium containing Antacids II. Magnesium containing antacids III. Aluminum Containing antacids IV. Combination Antacids i ) Calcium carbonate ii) Tribasic Calcium phosphate i ) Magnesium Carbonate ii) Magnesium hydroxide iii) Magnesium phosphate iv) Magnesium oxide v) Magnesium citrate vi) Magnesium trisilicate i ) Aluminium hydroxide ii) Aluminium phosphate iii) Aluminium carbonate gel iv) Aluminum Phosphate v) Dihydroxyaluminium sodium carbonate vi) Dihydroxyaluminium aminoacetate i ) Aluminium hydroxide gel + Magnesium hydroxide ii) Aluminuim hydroxide gel + Magnesium trisilicate iii) Simethicone containing antacids iv) Calcium Carbonate containing antacids v) Magaldrate : Monoalium hydrate + hydrated magnesium aluminate

8. COMBINATION ANTACIDS ARE PREFFERED OVER OTHER ANTACIDS Calcium and Aluminium containing antacids produce a constipating effect. They inhibit smooth muscle contraction of GIT (peristalsis) and thus delays evacuation of stools from bowels. Magnesium containing antacids produce a laxative effect. Mg is an osmotic laxative. It increases the bulk of stool by drawing in water and thus stimulate peristalsis. THEREFORE , COMBINATION ANTACIDS ARE USED. 1. Calcium + Magnesium salts 2. Aluminium + Magnesium salts Simethicone is also used as an additive in many antacids.

9. Simethicone acts as a Defoaming agent. They increase the surface tension of bubbles causing smaller bubbles to either break or to form larger bubbles which easily evacuates itselves by burping or flatus. FAMOUS BRANDS AND THEIR INGREDIENTS 1. GELUSIL Ingredients : Al(OH) 2 + Mg(OH) 2 + Simethicone 2. DIGENE Ingredients : Al(OH) 2 + Mg(OH) 2 + Simethicone + Sodium carboxy methylcellulose SODIUM BICARBONATE Physical Properties Colorless Odorless Powder form/Crystalline Slightly saline/alkaline in taste Soluble in water M.p : 50°C B.P.: 851° C

10. MEDICINAL USES OF SODIUM BICARBONATE As Systemic antacid. NAHCO 3 neutralizes the acid in the blood to maintain a normal pH. 1. SYSTEMIC ANTACID As systemic acidifier, it is given in the form of intravenous injection Indicated in:- Loss of Bicarbonate ion due to diarrhea/vomiting Chronic Kidney Disease/ Dialysis Diabetic ketoacidosis 2. NON-SYSTEMIC ANTACID NaHCO 3 tablets are used to treat stomach acidity, acid indigestion and heartburn. It provides quickest relief from stomach acidity. However, it is rapidly absorbed into the bloodstream where it produces alkalosis. As action is not prolonged, it is generally not used for this purpose

11. 3. GASTRIC LAVAGE AND LAXATIVE NaHCO 3 + POLYETHYLENE GLYCOL is dissolved in water and is given as an gastrointestinal lavage and laxative prior to GIT surgery / Gastroscopy . 4. HYPERKALEMIA In case of metabolic acidosis, NaHCO 3 causes alkalosis and therefore force K+ ions back into muscular cells through H+/K+ exchange mechanism. 5. AS AN ANTIDOTE NaHCO 3 absorption of Aspirin and Tricyclic antidepressprevents ants into bloodstream, in case of a overdosage by producing a basic environment. The above cited drugs require an acidic environment to be absorbed. 6. AS ADDITIVE IN LOCAL ANAESTHETICS AND COMPONENT IN MOFFET’S SOLUTION As an additive in solutions of local anaesthetics , to relive pain from injection and in speeding up the onset of action. In Moffet’s Solution(used prior to nasal surgeries)

12. 7. AS COMPONENT IN EFFERVESCENT TABLETS Along with tartaric acid, NaHCO 3 is used as a excipient in effervescent tablets. When such a tablet is dissolved in water, the bicarbonate leaves the medication as C0 2 ASSAY OF SODIUM BICARBONATE PRINCIPLE: ACID-BASE TITRATION (ACIDIMETRY) 1.5 g NaHCO 3 + 50 ml CO 2 free water + Indicator (Methyl orange) 1 M HCl solution REACTION: NaHCO 3 + HCl NaCl + CO 2 + H 2

13. Excess drop of HCl Ionized Methyl orange (YELLOW COLOUR) Non-ionized methyl orange (ORANGE COLOUR) COLOUR CHANGE Methyl Orange in Basic solution (YELLOW) Methyl Orange in Mildly Acidic Solution (ORANGE) Ionized Methyl orange Non-ionized methyl orange

14. Repeat Titration to get concordant value. Note down the titre value/ Amount of HCl consumed Equivalent Weight Factor: 1ml of 1M HCl Ξ 0.08401g of NaHCO 3 Calculate the percentage purity of NAHCO 3 by following equation: % purity = Titre Value x Normality of HCl x Eq. Wt. Factor x 100 Sample Weight ALUMINIUM HYDROXIDE Colourless Odourless Insoluble in water Soluble in acidic/ alkaline solutions M.P. = 300°C Amorphous powder

15. MEDICINAL VALUE OF ALUMINIUM HYDROXIDE 1. AS AN ANTACID Al(OH) 3 gel neutralizes the acid in the stomach. Thereby, it relieves acidity, heartburn and abdominal discomfort. Being insoluble, it never raises the pH of stomach above 7. therefore, it does not trigger excess of acid production However, because it inhibits smooth muscle cell contraction of GIT/ Peristalsis, it can result in constipation. COMPOSITION OF AL(OH) 3 GEL Amorphous Al(OH) 3 + Small amounts of Al(C0 3 ) 3 Flavoring agents: Sorbitol , Saccharin, Sucrose, Peppermint oil etc. Suitable antimicrobial agents

16. 3. AS VACCINE ADJUANT Al(OH) 3 is used as an adjuant in some vaccines such as the Anthrax Vaccine. It stabilizes the protein/inactivated bacteria and viruses by absorbing it. This absorption of these elements prevent its precipitation or its sticking to the walls of the containers. 2. HYPERPHOSPHOTEMIA In this condition, excess of phosphates builds up in the blood due to insufficient excretion of phosphates from kidneys. Al(OH) 3 is used as phosphate binder in hyperphosphotemia . Al salts bind to phosphates in intestine and reduce the amount of phosphates that can be absorbed. MAGNESIUM HYDROXIDE Color: Silvery white Slightly soluble in water Density: 2.345 g/cm 3 Forms MgO when heated to 360°C Odorless

17. MAGNESIUM HYDROXIDE MIXTURE 1. Extemporaneous preparation/ Readily available Light Magnesium Oxide Water MEDICINAL USES OF Mg(OH) 2 2. Also known as Milk of Magnesia 1. As an antacid, for the relief of acidity, heartburn and dyspepsia 2. As a laxative, for relief from occasional constipation Magnesium absorbs water in the intestinal lumen. This increases the size of stool due to which peristalsis is forceful. Low water solubility of Magnesium permits it to remain in the stomach for longer duration and exhibit its acid neutralizing property effectively. 3. Owing to its ability to adsorb water, it is used as an antiperspirant in talcum powders 4. Used topically in the treatment of canker sores/ Aphthous stomatitis

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