They are weak bases that neutralize gastric acidity increasing pH of the stomach to 5 or above leading to decrease total acid delivery to the duodenum and inhibit pepsin activity, so decreasing pain associated with ulcer and may promote healing
Classification
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Antacids are classified into systemic (absorbable) e.g. Sodium Bicarbonate (NaHCO3) and Calcium Carbonate and
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non-systemic (Non-absorbable), e.g. Aluminum Hydroxide and Magnesium Salts.
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Combination: Gaviscon
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All of them are safe except the systemic absorbable derivatives Sodium/Calcium
Uses of Antacids
Symptomatic treatment of gastric, duodenal ulcer and oesophagitis
Adverse Effects of Antacids
1-Change in bowel habits e.g., AL & Ca based antacids cause constipation, while Mg-based causes diarrhea. Either combining or alternating compounds with these effects can treat this problem.
2-Cation absorption (Na, Ca, Mg, Al)
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Increase Ca++ leads to systemic hypercalcaemia with formation of calculi and milk alkali syndrome especially in renal impairment. - may be contraindicated with patients who drink milk, unless theres no complaints, no hypercalcemia
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Increased Mg++ causes muscle weakness and fatigue
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Increased Na+ absorption leading to systemic alkalosis.
3-AL binds phosphate and prevents its absorption leading to hypophosphatemia with muscle weakness and resorption of bone.
4-Rebound hypersecretion of Z HCl with Ca++ and NaHCO3 containing antacids.
Drug Interactions
Ca, AL and Mg, decrease absorption of tetracycline, Al (OH)3 decrease absorption of digoxin, isoniazid (INH), warfarin, anticholinergic drugs and iron.
The increase in gastric pH decrease the absorption of acidic drugs. Systemic antacids increase excretion of drugs e.g quinidine.