Gastrointestinal Agents

1. Gastrointestinal Agents Acidifying agents  Antacids  Protectives  Adsorbents  Cathartics or Laxatives

2. Inorganic Gastrointestinal Agents Inorganic agents used to treat gastrointestinal disorders include: • Products for altering gastric pH -Acidifying Agents: Used to treat achlorhydria (absence of HCl in the gastric secretion) e.g.- Diluted HCl -Antacids: Used to treat hyperchlorhydria and peptic ulcer. 2) Protectives for intestinal inflammation 3) Adsorbents for intestinal toxins 4) Cathartics or laxatives for constipation

3. Antacids

4. Gastric Gas in the stomach Discomfort feeling in the stomach Heat Burn Indigestion

5. Introduction to antacids • Definition of antacids: (Gk. Anti-against;acids) Antacids are basic substances which on ingestion react with gastric acid and lower the acidity of gastric content, chiefly used in the treatment of hyperchlorhydria and peptic ulcer. In recent years, Antacids are compared quantitatively in terms of their Acid-Neutralizing capacity, defined as the quantity of 1 N HCl (expressed in milliequivalents) that can be brought to pH 3.5 in 15 minutes.

6. Introduction to antacids  Composition of antacids: The hydroxide is the base most commonly employed in antacids,but carbonate,bicarbonate and trisilicate ions are also used. The therapeutic efficacy and adverse effects depend on the metallic ion with which the base is combined and this is usually aluminium, magnesium or sodium.  Mode/mechanism of action of antacids: Antacids act as weak alkaline bases. They neutralize the excess gastric hydrochloride and relieve pain of peptic ulcer by raising the pH of gastric contents to about 4 (pain occurs when pH falls below 3.5).

7. Chemistry of antacids action:  The chemistry of antacid action is simple-the reduction of hydronium ion concentration by reaction with a base stronger than water. H3O+ + BI - = HBI + H2O  The extent to which the reaction proceeds is a function of the relative strengths of water as a base and the antacid as a base but the effect is an increase in pH.  Different antacids react with HCl to form chlorides, water and carbon dioxide, neutralizing HCl by the following chemical reactions. Al(OH)3 + 3HCl = AlCl3 + 3H2O (slow) Mg(OH)2 + 2HCl = MgCl2 + 2H2O (slow/moderate) CaCO3 + 2HCl = CaCl2 + H2O + CO2 (fast) NaHCO3 + HCl = NaCl + H2O + CO2 (fast)

8. Criteria of Ideal Antacids  The antacid should not be absorbable or cause systemic alkalosis.  It should not be laxative or cause constipation  It should buffer in the pH 4-6 range  It should be rapidly effective and maintain its effect over a long period of time.  It should probably inhibit pepsin but should not completely inactivate peptic digestion.  It should not produce rebound acidity or excessive eructation (belching).  It should not cause large evolution of gas by reacting with gastric HCl.  It should not affect the absorption of food, nutrient and vitamin.  It should be non-irritant to stomach, intestine and should not cause diarrhea.  It should be non-toxic, and palatable.  It should be cheap and available.

9. Criteria for antacid products In order for a product to be labeled an antacid according to FDA Antacid Panel it must consist of one or more approved (active) ingredients. Each active ingredient must contribute at least 25% of the total acid-neutralizing capacity of the product.  The finished product must contain at least 5mEq/dose unit of acid-neutralizing capacity and raise the pH of gastric secretions to 3.5 or greater within 15 minutes.  No more than four active antacid ingredients can be combined in any one product.

10. Classification of Antacids Antacids are commonly classified in two groups: Systemic Antacids & Nonsystemic antacids Systemic Antacids: Antacids(water soluble) which are absorbed in the systemic circulation (usually from the gut) and may cause metabolic alkalosis are called systemic antacids. Common systemic antacids are: Sodium Bicarbonate, Sodium citrate, Sodium acetate, and Potassium citrate.

11. Classification of Antacids Nonsystemic Antacids: Antacids which are not absorbed from the gut and does not interrupt acid base balance (metabolic alkalosis) are called nonsystemic antacids. Non systemic antacids are divided into-Buffer antacid & Non-buffer antacid. Buffer antacid:They limit the rise in pH of the gastric contents to below neutrality. e.g. Aluminum Hydroxide Gel [Al(OH)3], Magnesium hydroxide [Mg(OH)2], Magnesium Trisilicate [2MgO.3SiO2.xH2O] Non-buffer antacid:They potentially permit the elevation in pH even above neutrality. e.g. Calcium carbonate [CaCO3], Calcium phosphate [Ca3(PO4)2], Magnesium oxide [MgO], Magnesium Carbonate [MgCO3]

12. Antacid Therapy Aim of antacid therapy: The chief objective for administering an antacid is to reduce or neutralize excess gastric hydrochloride and the ultimate goal of therapy is to bring the gastric contents to pH between 3.5 to 5. Factors in selecting an antacid for therapy: The patients condition, Systemic Vs Nonsystemic action, Neutralizing capacity of antacid, Dose of antacid, Dose-Interval and Cost etc. Indications: Antacids are prescribed by the physicians for the symptomatic relief of peptic ulcer, gastritis, peptic esophagitis, heart burn, acid indigestion, sour stomach and dyspepsia. Side effects of antacids: Rebound acidity, systemic alkalosis, sodium overload (problem for sodium restricted patients), laxative effect (Mg containing antacids), constipating effects (Aluminum containing antacids),

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