Antacids are basic substances which neutralize gastric acid and raise pH of gastric contents.
They are available and are taken by mouth to quickly relieve occasional heartburn, the major symptom of gastroesophageal reflux disease and indigestion. Treatment with antacids alone is symptomatic and only justified for minor symptoms.
Antacids are distinct from acid-reducing drugs like H2-receptor antagonists or proton pump inhibitors and they do not kill the bacteria Helicobacter pylori, which causes most ulcers.
Non-particulate antacid (sodium citrate, magnesium trisilicate) increase gastric pH with little or no effect on gastric volume.
Sodium citrate should be given within 1 hour of surgery to be the most effective.
Types of antacids :-
1. Systemic Antacids
- Sodium bicarbonate = It is water soluble, acts instantaneously, but the duration of action is short. It is a potent neutralizer (1 g- 12 mEq HCL), pH may rise above 7. However, it has several de-merits:
- Absorbed systemically: large doses will induce alkalosis.
- Produces CO2, in stomach → distention, discomfort, belching, risk of ulcer perforation.
- Acid rebound occurs, but is usually short lasting.
- Increases Na+ load: may worsen edema and CHF.
Use of sod. bicarbonate is restricted to casual treatment of heartburn. It provides quick symptomatic relief. Other uses are to alkalinize urine and to treat acidosis.
Sodium citrate properties similar to sod. bicarbonate:
1 g neutralizes 10 mEq HCI; CO2 is not evolved.
2. Non Systemic Antacids
These are insoluble and poorly absorbed basic compounds.
They react in stomach to form the corresponding chloride salt. The chloride salt again reacts with the intestinal bicarbonate so that HCO, is not spared for absorption-in acid-base distur bance occurs.
However, small amounts that are absorbed have the same alkalinizing effect as NaHCO3.
- Magnesium trisilicate
It has low solubility and reactivity. 1g can react with 10 mEq acid, but in clinical use only about 1 mEq is neutralized.
About 5% of administered Mg absorbed systemcally- may cause problem if renal function is inadequate.
All Mg salts have a laxative action by generating osmotically active MgCl, in the stomach and through Mg ion induced cholecystokinin release. Soluble Mg salts are used as osmotic purgatives.
- Aluminium hydroxide
It is a weak and slowly reacting antacid. On keeping it slowly polymerizes to variable extents into still less reactive forms.
Thus, the ANC of a preparation gradually declines on storage. Also, the product from different manufacturers may have differing ANCs;
Usually it varies from 1-2.5 mEq/g. Thus, 5 ml of its suspension may neutralize just 1 mEq HCI. As such, little worthwhile acid neutralization is obtained at conventional doses.
The Almunium ions relax smooth muscle. Thus, it delays gastric emptying. Alum. hydrox. frequently, causes constipation due to its smooth muscle relaxant and mucosal astringent action.
Alum. hydrox. binds phosphate in the intestine and prevents its absorption-hypophosphatemia occurs on regular use. This may:-
- cause osteomalacia
- be used therapeutically in hyperphosphatemia and phosphate stones.
Small amount of Al that is absorbed is excreted by kidney. This is impaired in renal failure aluminium toxicity (encephalopathy, osteoporosis) can occur
ALUDROX 0.84 g tab, 0.6 g/10 ml susp.
- Magaldrate
It is a hydrated complex of hydroxy magnesium aluminate that initially reacts rapidly with acid and releases alum, hydrox. which then reacts more slowly.
The freshly released alum hydrox. is in the unpolymerized more reactive form. Thus, magaldrate cannot be equated to a physical mixture of mag and alum. hydroxide. It is a good antacid with prompt and sustained neutralizing action.
STACID 400 mg tab, 400 mg/5 ml susp., ULGEL 400 mg with 20 mg simethicone per tab or 5 ml susp.
- Calcium carbonate
It neutralizer (1 g It is a potent and rapidly acting acid → 20 mEq HCI), but ANC of commercial preparations is less and variable due to differing particle size and crystal structure. Though it liberates CO, in the stomach at a slower rate than NaHCO3, it can cause distention and discomfort. The Cations are partly absorbed.
Uses :-
Antacids are no longer used for healing peptic ulcer, because they are needed in large and frequent doses, are inconvenient, can cause acid rebound and bowel upset, afford little nocturnal protection and have poor patient acceptability.
They are now employed only for intercurrent pain relief and acidity, mostly self-prescribed by the patients as over the counter preparations. Antacids to be used for nonulcer dyspepsia and minor episodes of heartburn.
Gastroesophageal reflux Antacids afford faster symptom relief than drugs which inhibit acid secretion, but do not provide sustained benefit. May be used off and on for acid eructation and heartburn.
Side effects :-
Versions with magnesium may cause Diarrhoea, and brands with calcium or aluminium may cause constipation and rarely, long-term use may cause kidney stones.
Long-term use of versions with aluminium may increase the risk for getting osteoporosis.
