Antacid

An antacid is a substance which neutralizes stomach acidity and is used to relieve heartburn, indigestion, or an upset stomach. Some antacids have been used in the treatment of constipation and diarrhea. Marketed antacids contain salts of aluminium, calcium, magnesium, or sodium. Some preparations contain a combination of two salts, such as magnesium carbonate and aluminium hydroxide (e.g., hydrotalcite).

Antacids are available over the counter 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. Alternative uses for antacids include constipation, diarrhea, hyperphosphatemia, and urinary alkalization. Some antacids are also used as an adjunct to pancreatic enzyme replacement therapy in the treatment of pancreatic insufficiency.

Non-particulate antacids (sodium citrate) increase gastric pH with little or no effect on gastric volume, and therefore may see some limited use in pre-operative procedures. Sodium citrate should be given within one hour of surgery to be the most effective.

Conventional effervescent tablets contain a significant amount of sodium and are associated with increased risk of adverse cardiovascular events according to a 2013 study. Alternative sodium-free formulations containing magnesium salts may cause diarrhea, whereas those containing calcium or aluminium may cause constipation. Long-term use of antacids containing aluminium may increase the risk of developing osteoporosis. In vitro studies have found a potential for acid rebound to occur due to antacid overuse, however the significance of this finding has been called into question.

When an excess amount of acid is produced in the stomach, the natural mucous barrier that protects the lining of the stomach can degrade, leading to pain and irritation. There is also potential for the development of acid reflux, which can cause pain and damage to the esophagus. Antacids contain alkaline ions that chemically neutralize stomach gastric acid, reducing damage to the stomach lining and esophagus, and relieving pain. Some antacids also inhibit pepsin, an enzyme that can damage the esophagus in acid reflux.

Antacids do not directly inhibit acid secretion, and thus are distinct from acid-reducing drugs like H₂-receptor antagonists or proton pump inhibitors. Antacids do not kill the bacterium, Helicobacter pylori, which causes most ulcers.

Antacids are mainly classified into two categories:

Antacids are known to interact with several oral medications, including fluoroquinolone and tetracycline antibiotics, iron, itraconazole, and prednisone. Metal chelation is responsible for some of these interactions (e.g. fluoroquinolones, tetracyclines), leading to decreased absorption of the chelated drug. Some interactions may be due to the pH increase observed in the stomach following antacid ingestion, leading to increased absorption of weak acids, and decreased absorption of weak bases.^{[citation needed]} Antacids also cause an increase in pH of the urine (alkalization), which may cause increased blood concentrations of weak bases, and increased excretion of weak acids.