Antacid Preparations – This book covers the entire syllabus of “Pharmacology” prescribed by BNMC- for diploma in nursing science & midwifery students. We tried to accommodate the latest information and topics. This book is an examination setup according to the teachers’ lectures and examination questions.
At the end of the book, previous questions are given. We hope in touch with the book students’ knowledge will be upgraded and flourish. The unique way of presentation may make your reading of the book a pleasurable experience.
Antacid Preparations
Antacids are basic substances that reduce gastric acidity by neutralizing HCl.
Antacids are drugs used to produce relief of peptic ulcer pain associated with hyperchlorhydria. They act by neutralizing gastric acid and thus raising the gastric pH, which has the effect of inhibiting peptic activity, which particularly ceases at PH 5.
Chemically: antacid consists of weak basic part and the metallic cataions.
| Weak basic part | In the form of: OH, oxide,HCO3 | Responsible for the neutralization of acid (HCI |
| Metallic cataions | Al, Mg, Na, Ca, K | Responsible for the Pharmacodynamics properties and adverse effects. |
Classification of Antacids:
| Synthetic Antacid | Properties |
| ➤ NaHCO3 ➤NaCO3 ➤KHCO ➤ Na-citrate ➤ Na-acetate | ➤ Absorbed in the system. ➤ Quick onset of action. ➤ Soluble. ➤ Produce acid-based’s ➤ abnormality (metabolic) |
| Buffer group ➤ Mg trisilicate ➤ Al (OH)3 gel ➤ AIPO4 Non-buffer group ➤ CaCO3 Ca(OH)3 ➤ MsCO3, Mg(OH | ➤ Not absorbed in system. Insoluble. ➤No acid base abnormality ➤Diarrhoea ➤ Constipation is the common side effect. |
Criteria of an ideal Antacid:
An ideal antacid should have the following criteria:
1. It should be neutral in aquous suspension, but be capable of neutralising acid.
2. It should produce its effect rapidly & maintain its action for several hours.
3. It should not cause irritation of stomach and intestine.
4. It should not cause Gastrointestinal disturbances, such as Diarrhoea. Constipation.
5. It should not produce acid rebound.
6. It should not disturb the acid-base balance, cause alkalosis or alkalise the urine.
7. It should not affect absorption of food, nutrients and vitamins.
8. Should produce optimum PH in the stomach.
9. Should not completely inactivate peptic digestion.
10. It should be palatable, cheap and available
Pharmacological action of antacid:
1. Acid neutralization: antacids act with HCI and neutralizes it (chemical antagonism)
2. Absorb pepsin (anti-peptic; pepsin causes ulceration: when antacid neutralises acid there is raise of ptr (3.5). At this PH pepsin becomes inactive. Thus protect the gastric mucosa.
3. Antacids coagulate mucoprotein at the base of the ulcer (Aluminum containing antacids).
4. Prevent acid reflux to the lower part of oesophagus.
5. Antacids can be effective in promoting healing of the duodenal ulcer.
Indication of Antacid:
1. Peptic ulcer: Gastric and duodenal ulcer.
2. Zollinger-Ellison-Syndrome.
3. Reflux oesophagitis, hyperchlorhydria.
4. Prophylaxis of stress ulcer.
5. Upper GIT bleeding.
6. Acute pancreatitis, nephrolithiasis (PO+ calculi)
7. As anti-diarrhoeal agent, e.g. Al(OH)3
8. As laxative, e.g. Mg(OH)2.
9. Systemic acidosis and mineral acid poisoning.
10. With other drugs (aspirin, steroid, indomethacin
Contraindication of antacid:
Pyloric stenosis and systemic alkalosis
Adverse effects of antacids:
| Systemic antacid Na antacid (>30% absorbed) | Metabolic alkalosis due to the absorption of basic part. Acid-base abnormality due to absorption of cationic moiety. Na containing antacids are dangerous in patient with cardiac and renal diseases. |
| Non-systemic antacids Al antacid (5-6% absorbed) | Constipation: aluminum relaxes the smooth muscle of the gut, so reduces gastric motility, d Encephalopathy, osteodystrophy (due to systemic absolption of Al) |
| Mg antacid (5-6% absorbed) | Diarrhoea |
| Ca antacid (6-16% absorbed) | Diarrhoea, Hypercalcemia Milk alkali syndrome. Cardiac arrhythmia |
Choice of antacids preparations
The most preferable antacids is the combination preparation of Al(OH)3 + Mg(OH)2 + Simerhicone.
Because:
A. It is a very rapidly acting antacid component, which can achieve neutralisation within a few minutes.
B. A more sustained effect.
C. Minimizes the undesirable effect by using a lower dose of each component.
D. One component antagonises side effects of another (e.g. laxation versus constipation). Thus antacid containing Al & Mg compounds do not change bowel function drastically.
E. Al(OH)3 and Mg(OH)2 taken concurrently, have relatively little effect on gastric emptying.
| Interaction | Possible Cause |
| Iron, Digoxin + antacids Reduce Bioavailability of the iron and Disoxin | Antacids prevent absorption of iron. Digoxin from intestine |
| Tetracycline + Antacids Reduce Bioavailability of the tetracycline | Decreases the gastrointestinal absorption of tetracycline by antacids. |
| Warfarin + Antacids Reduce Bioavailability of the warfarin | Antacid blocks the absorption of warfarin from the intestine |
Systemic Antacids
Systemic Antacids
Systemic antacids are so called as they are soluble and completely absorbed in the systemic circulation and produce systemic alkalosis.
Advantage of systemic antacids
1. It relief pain quickly by direct neutralisation of HCl.
2. It also acts as a carminatire.
3. It produces neither constipation nor diarrhoea.
Disadvantage of systemic antacids
1. Short duration of action.
2. Causes systemic alkalosis or rebound acidity.
3. Bleaching and gastric distension occur due to CO2 release,
4. May cause oedema and heart failure in patient with cardiac or renal disease,
5. May retard peptic digestion by raising gastric PH. May cause perforation in patient with gastric ulcer.
6. Causes milk-alkali syndrome.
7. Not given in patient with Na ion restricted diet.
8. Weight gain.
Effects of Systemic Antacid (e.g. NaHCO3):
A. Systemic alkalosis: NaHCO3 + Gastric HCI NaCl + H2O + CO2 When a systemic antacid is administered, it neutralises gastric HCI. So, equivalent amount of intestinal HCO3 remains neutralised and absorbed. The net effect of this HCOI absorption shifts the acid base balance of body fluids towards alkaline site and produces systemic alkalosis which is characterised by loss of appetite, weakness, mental confusion etc
B. To correct the systemic alkalosis, kidney excretes excess HCO3 and cations. So. the urine becomes alkaline. The repeatecl alkalisation of urine during chronic administration of systemic antacid, predispose to phosphatic nephrolithiasis and renal insufficiency.
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