Antacids revisited - A review of their clinical pharmacology and recommended therapeutic use

Antacids are commonly used self-prescribed medications. They consist of cal cium carbonate and magnesium and aluminum salts in various compounds or com binations. The effect of antacids on the stomach is due to partial neutrali sation of gastric hydrochloric acid and inhibition of the proteolytic enzym e, pepsin. Each cation salt has its own pharmacological characteristics tha t are important for determination of which product can be used for certain indications. Antacids have been used for duodenal and gastric ulcers, stres s gastritis, gastro-oesophageal reflux disease, pancreatic insufficiency, n on-ulcer dyspepsia, bile acid mediated diarrhoea, biliary reflux, constipat ion, osteoporosis, urinary alkalinisation and chronic renal failure as a di etary phosphate binder. The development of histamine H-2-receptor antagonis ts and proton pump inhibitors has significantly reduced usage for duodenal and gastric ulcers and gastro-oesophageal reflux disease. However, antacids can still be useful for stress gastritis and non-ulcer dyspepsia. The rece nt release of proprietary H-2 antagonists has likely further reduced antaci d use for non-ulcer dyspepsia. Other indications are still valid but repres ent minor uses. Antacid drug interactions are well noted, but can be avoided by reschedulin g medication administration times. This can be inconvenient and discourage compliance with ether medications. All antacids can produce drug interactio ns by changing gastric pH, thus altering drug dissolution of dosage forms, reduction of gastric acid hydrolysis of drugs, or alter drug elimination by changing urinary pH. Most antacids, except sodium bicarbonate, may decreas e drug absorption by adsorption or chelation of other drugs. Most adverse effects from antacids are minor with periodic use of small amo unts. However, when large doses are taken for long periods of time, signifi cant adverse effects may occur especially patients with underlying diseases such as chronic renal failure. These adverse effects can be reduced by mon itoring of electrolyte status and avoiding aluminum-containing antacids to bind dietary phosphate in chronic renal failure. Antacids, although effecti ve for discussed indications of duodenal and gastric ulcer and gastro-oesop hageal reflux disease, have been replaced by newer, more effective agents t hat are more palatable to patients. Antacids are likely to continue to be used for non-ulcer dyspepsia, minor e pisodes of heartburn (gastrooesophageal reflux disease) and other clear ind ications. Although their wide spread use may decline, these drugs will stil l be used, and clinicians should be aware of their potential drug interacti ons and adverse effects.