Antacids Information PDF

Antacids Weak bases that NEUTRALIZE gastric acid They DO NOT INHIBIT gastric acid secretion This reaction then is an Acid/Base reaction - Antacids act by neutralizing gastric acid and thus raising the gastric pH - Raising gastric pH 1 point neutralizes 90% of the gastric acid - Inhibiting pept...

Antacids Weak bases that NEUTRALIZE gastric acid They DO NOT INHIBIT gastric acid secretion This reaction then is an Acid/Base reaction - Antacids act by neutralizing gastric acid and thus raising the gastric pH - Raising gastric pH 1 point neutralizes 90% of the gastric acid - Inhibiting peptic activity, which practically ceases at pH 5 - they can produce healing of duodenal ulcers Active ingredient: Basic metal salt Cations used are highlighted in Red Anions: OH-, O2-, CO32-, HCO3-, HPO3-, Trisilicate (Mg), amino acetate (Al)  Common Antacid Compounds Antacids are weak bases that are used to neutralize excess stomach acid Most antacids are weak inorganic bases Common examples include: CaCO3 NaHCO3 Mg trisilicate Mg(OH)2 (Milk of Magnesia) Al(OH)3 5  Common Antacids Calcium Carbonate Magnesium Salts Aluminium Salts Bisodol Milk of Magnesia Maalox Calcichew Maalox Gaviscon Actonel Most potent antacid ingredient; Less potent that Calcium Mild and slow acting acts rapidly with more prolonged Slow acting antacid, last longer action than sodium bicarbonate Can use hydroxide, Most stable form of phosphate & trisilicate aluminium salts under normal conditions  Relevant Quality Standards Antacids are subject to various pharmacopeial tests/ regulatory requirements FDA: must >25% of total Minimum dose of drug when added to 10 mL of 0.5 N HCl and 40 mL of water must raise pH to 3-5 at end of 10 min at 300 rpm The solution of drug must be pH>3.5 Acid Neutralising Capacity This is a way of expressing the acid neutralising power of an antacid and it is pharmacopeial test. It is established using a back-titration in which excess acid is added and the residue is estimated by titration with sodium hydroxide Rate is important along with ANC Reactions - Ca CaCO3 + 2 HCl → CaCl2 + H2O + CO2 CaCl2 + CO32- → CaCO3 + Cl- (higher pH in intestine) Some unchanged calcium is absorbed by the gut, which can raise the pH of the blood causing alkalosis – can affect proteins Calcium is then removed through the renal system Magnesium Mg(OH)2 + 2HCl → MgCl2 + 2H2O Magnesium oxides, hydroxides and carbonates are poorly soluble, only chloride are soluble. Aluminium Al(OH)3 + 3HCl → AlCl3 + 3H2O Al(H2O)63+ Solubility of Al increases as pH decrease, above pH>5 neutralizing effect will stop Al3+ + PO43- → AlPO4 (insoluble) Inadequate amount of phosphate ions will cause Al3+ to be absorbed It will rebind back at soft tissue or bones where phosphates are found Alginates Glucuronic-mannuronic acid polymer Forms hydrogels Raft acts as barrier Reduces reflux in oesophagus Main ingredient in Gaviscon Alginates and Antifoaming Agents Antacids are often combined with alginates and anti- foaming agents. Aliginates float on the stomach contents to form a neutralizing layer preventing reflux of stomach acids up into the esophagus. Hence they help to prevent acid reflux or heart burn. Anti-foaming agents such as simethicone (dimethicone) prevent the formation of gases and reduce flatulence.  Clinical Uses ✓ Treatment of GORD (infrequent heartburn) ✓ Treatment of duodenal ulcers, although anti-H2 and proton pomp inhibitors are more effective ✓ No prevention of NSAID-associated ulcers  Treatment of GORD Patients with infrequent heartburn (fewer than 3 times per week) or isolated episodes Antacids provide rapid acid neutralization - they afford faster symptom relief Their effect is short-lived (1-2 h) Antacid – General Side Effects Antacids are relatively harmless but they can have minor contraindications Impair normal bowel function Some preparations contain salt – clinical implications Problems associated with reduced gastric acidity  Caution!!! Some preparations contain high concentrations of salt Avoid in patients with hypertension or cardiac failure. Problems with Reduced Gastric Acidity Impaired ability to absorb some nutrients - iron Low gastric pH – defensive mechanism  Drug Interactions Antacids should preferably not be taken at the same time as other drugs since they may impair absorption of numerous compounds ✓  Calcium Carbonate - Potent usable antacid. It can completely neutralize gastric acid. - About one-third of the administered calcium is absorbed - Calcium deficiency/Avoid in patients with hypercalcaemia (malignancy) - Calcium-containing kidney stones are slight risks. - Can raise the pH of the blood causing alkalosis - Calcium may cause constipation  Magnesium Hydroxide - Insoluble powder that forms magnesium chloride in the stomach - Its antacid effect is potent - It is mainly not absorbed - Mg2+ retained in GIT lumen is osmotically active component and can induce diarrhoea - Renal impairment - Encephalophaty  Magnesium Trisilicate - Compound of magnesium oxide and silica - Insoluble powder that reacts slowly with the gastric juice forming magnesium chloride and colloidal silica - It is not as potent as Mg hydroxide - Mg2+ retained in GIT lumen is osmotically active component and can induce diarrhoea - Silica-based renal stones reported on long-term treatment  Aluminium Hydroxide - It forms aluminium chloride in the stomach - Raises the pH of the gastric juice up to 4 - It acts gradually and its effect continues for several hours - Some aluminium chloride may be absorbed; could affect CNS if renal function is impaired - Constipation - Al hydroxide combines with phosphates in the GIT Phosphate Metabolism  Aluminium Hydroxide – Management of chronic renal failure - Renal impairment - Encephalopathy  Sodium Bicarbonate - Water soluble - Acts rapidly & raises the pH up to 7.4 - Carbon dioxide is liberated and this causes belching  Sodium Bicarbonate - large doses or frequent administration can cause alkalosis - Na+ can be also absorbed & induce hypertension CAUTION: ✓Hypertension ✓Cardiac Failure ✓Chronic Kidney Disease  Choice of Antacid Underlying conditions Patient preference Pregnancy and Breastfeeding Generally safe – consideration if the mother has high blood pressure or chronic renal impairment Aluminium-containing antacids are safe to be used in pregnant women. The information regarding the use of these antacids in breastfeeding has not been studied Calcium-containing antacids, excessive use is to be avoided in pregnant women as calcium crosses the placenta. The amount of calcium reaching the fetus is dependent on the physiological changes in the mother. Maternal calcium intake also affects the amount of calcium excreted in breast milk; the currently prevailing opinion is that the use of calcium- containing antacids is safe during breastfeeding