Antacids. Pharmacology by Baqir Naqvi.pptx

Antacids. Pharmacology by Baqir Naqvi.pptx

1. ANTACIDS (Pharmacology & Therapeutics-1) Lecture By Dr. M. Baqir Raza Naqvi (BSc, Pharm-D, M. Phil-Pharmacology) Nazar College of Pharmacy DAKSON Institute of Health Sciences, Islamabad 1

2. Antacids These are the dugs which are given orally to neutralize the gastric HCl & raise the PH of stomach. OR These are the drugs which are used to reduce the hyperacidity of the stomach. Antacids are weak bases that react with gastric acid to form water and a salt to diminish gastric acidity . Indications Peptic ulcer, gastritis and heart burn etc. They come as a liquid or chewable tablets and capsules and can be bought from pharmacies and shops without a prescription (OTC drugs). 2

3. General mechanism of action of Antacids The gastric juice contains HCl and pepsin . Pepsin is a proteolytic enzyme ( breaks down proteins into smaller peptides) which causes perforation of stomach wall in hyperacidity (1-2 PH). The antacids raises the PH of acid from 1-2 to 3-4 or even 7 . At this PH the activity of pepsin is reduced . There is no perforation of stomach wall & therefore antacids are used to relieve the gastric pain . 3

4. Properties of ideal antacids 4

5. Acid rebound phenomenon 5

6. Classification of antacids 6

7. Non systemic antacids “ These are the antacids which are not absorbed through GIT and do not enter the systemic circulation . ” These are as follows; 1. Physically Acting: They absorb acid and form a protective coating on the surface of mucosa. These includes; a). Milk b). Mucine c). Resin 2. Physico-chemically acting: They form protective coating as well as neutralize HCl by chemical reactions . These includes; a). Aluminum hydroxide b). Aluminum phosphate c). Mg tri silicate 7

8. 3. Chemically acting “These antacids neutralize the acid by chemical reactions .” These includes ;;; Calcium carbonate --------------- (Ca COꝫ) Magnesium hydroxide ---------------- Mg (OH)₂ Magnesium oxide ---------- (MgO) M agnesium carbonate --------- (Mg COꝫ) 8 Non systemic antacids (Cont.)

9. Comparison b/w systemic & non-systemic Antacids Systemic Antacids Non Systemic Antacids They are inexpensive They are also inexpensive Easily Available Also Easily Available They are short acting They are long acting Soluble in gastric juice , so absorbed insoluble in gastric juice so not absorbed They produce alkalosis in blood Do not produce alkalosis in blood because not absorbed. Acid rebound phenomenon is produced because CO ₂ releases in stomach & increase the secretions of acid in stomach. They do not produce Acid rebound phenomenon because they do not release CO ₂ in stomach. 9

10. Pharmacology of systemic antacids 1. Sodium bicarbonate It is a colorless & odorless powder with alkaline taste. It is soluble in water & gastric juice. Mode of action It acts chemically & neutralize the gastric acid . When it is taken orally it enters the stomach & rapidly neutralize the HCl but its duration of action is short. 10

11. Mode of action (Cont.) The excess NaHCO3 is rapidly absorbed and causes systemic alkalosis . NaHCO ₃ + HCl NaCl + H2O + CO2 CO2 evolved during the reaction causes distension of the stomach . Gastrin is released from the parietal cells of gastric gland and causes production of HCl. That’s why systemic antacids causes acid rebound phenomenon . 11

12. Acid rebound phenomenon 12

13. Clinical uses Adverse effects It’s a household remedy & provide rapid relief of heart burn. It is used to alkalinize the urine & thus effective in barbiturates & salicylates poisoning. It’s used in gout disease to prevent precipitation of uric acid. It is used locally on the skin as antipruritic in the form of moist paste or solution. It is an ingredient of many solutions e.g. mouth washes. 13 Prolonged use may lead to systemic alkalosis It may disturb acid base balance. It causes acid rebound phenomenon . Combined use with Ca+ containing antacids & milk may leads to milk alkali syndrome ( Hypercalcemia ), which causes irreversible renal damage. DOSE: 300 mg- 4 g.

14. 2. Sodium Citrate It has same pharmacology as sodium bicarbonate (Already discussed above) 14

15. 1. Aluminum hydroxide It is a white, tasteless, odorless, amorphous powder insoluble in water & gastric juice. Mode of Action It has dual nature of action, i.e. it acts physico-chemically. It neutralize the gastric acid by chemical reaction . It also act as adsorbent . it adsorb toxins and HCl. This adsorbed HCl is released into small intestine where it is neutralized . 15 Pharmacology of Non-systemic A ntacids

16. Mode of Action (Cont.) Al(OH) ₃ increase the PH of stomach up to 3 - 4 , at which the activity of pepsin is reduced . So there is no perforation of stomach wall Al(OH)₃ + 3HCl AlCl₃ + 3H₂O AlCl₃ formed during this reaction passes into the intestine where it reacts with phosphate present in the intestinal juice & form Al(PO₄) which is excreted through feces. So it leads to deficiency of phosphate . 16

17. Clinical Uses Used to reduce hyperacidity of stomach. Used to reduce acid dyspepsia . Used to reduce pain of gastric ulcer Used in heart burn. Used in hyper- phosphatemia . 17 Adverse effects Aluminum also acts as jelly which causes constipation . It causes Phosphate deficiency . Aluminum containing antacids causes constipation, because Aluminum does not absorb water or inhibits the absorption of water which leads to constipation . DOSE: Al(OH) ₃ tab. 0.5-1 g as chewable tablets. 5-15 ml as a mixture.

18. 2. Magnesium tri silicate It is a fine, white, odorless and tasteless powder insoluble in water and gastric juice. Mechanism of action It has dual mode of actions i.e. it acts physico-chemically. It consist of two parts Magnesium part and silicate part. Magnesium part neutralize the acid by chemical reaction. 18

19. Mechanism of Action; (Cont.) Mg₂(SiO)₃ + 2HCl 2MgCl₂ + 3SiO₂ + H₂O The formation of silicon dioxide (SiO₂) forms a coating on the surface of mucosal membrane of stomach & prevents the irritation of mucosal membrane from digestion of HCl. Silicate also act as adsorbent & adsorb toxins, gases and HCl in the stomach and release it into small intestines where it is again neutralized . MgCl₂ produced during chemical reaction reacts with HCO₃ of intestinal juice and forms Mg CO₃ which is excreted through feces. MgCl₂ + HCO₃ Mg CO₃ 19

20. 20 Clinical Uses Used to reduce hyperacidity of stomach. Used to reduce acid dyspepsia . Used to reduce pain of gastric ulcer. Used in heart burn. Adverse effects It may cause diarrhea . It causes hypermagnesemia and systemic toxicity . Chronic ingestion of silicon may cause kidney stone . In renal impairment, the conc. of Mg in blood causes CNS depression . Drug interactions It reduces the absorption of oral iron.

21. Contra-indications Magnesium tri silicate should not be given to appendicitis patients because it causes the rupture of appendicitis due to diarrhea. It is contraindicated in lactating mothers . It is contraindicated in 1 st trimester of pregnancy . 21

22. Other Magnesium containing Antacids All these have similar properties, therapeutic uses and adverse affects as magnesium tri silicate . The only difference is in their chemical reactions. 22 MgO + 2HCl → MgCl₂ + H₂O Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O MgCl₂ produced during chemical reaction reacts with HCO₃ of intestinal juice and forms Mg CO₃ which is excreted through feces.

23. In case of Magnesium carbonate, MgCO ₃ neutralize the HCl by chemical reaction but CO₂ is evokes. This CO₂ may lead to acid rebound phenomenon. 23 MgCO₃ + 2HCl → MgCl₂ + H₂O + CO₂

24. Thank you ! 24