Pharmacology of antacids

Keywords: antacid, gastric acid, ulcer prophylaxis


Antacids are usually alkaline substances that are used to neutralise excess acid in the stomach. Antacids were developed based on the hydroxides and carbonates of the group II and III metals, as well as the bicarbonates of the alkali metals. Antacids can be classified into two main classes being non-absorbable or absorbable antacids. Non-absorbable antacids have fewer side effects and further advantageous properties. Each antacid has a specific active ingredient which has a different effect on the gastric acid. Antacids act similar to when an acid reacts with a hydroxide; a salt and water are produced. Antacids are more effective in the form of suspension. The average therapeutic dose of an antacid is 10–15 ml of liquid or one to two tablets three to four times a day. These drugs have small volumes of distribution, undergo minimal hepatic metabolism and are excreted in faeces. Antacids that contain calcium, magnesium and aluminium ions are chelators. To avoid undesirable interactions, antacids are usually used two hours before or after taking any medication.

Stress ulcerations are common in intensive care unit (ICU) patients. The pathophysiology of the ulceration probably results from an imbalance between mucosal protection and gastric acid hypersecretion. Whilst prophylaxis was provided to every patient previously, it is wise to individualise the decision and to only provide it to high risk patients. For critically ill patients who are able to receive enteral medications and in whom prophylaxis is indicated, an oral proton pump inhibitor (PPI) is preferred rather than an alternative prophylactic agent. For critically ill patients who cannot receive enteral medications, an intravenous (IV) histamine 2 (H2) receptor blocker or IV PPI can be administered. Where PPIs or H2 blockers cannot be administered, sucralfate is a suitable oral alternative.

Author Biography

K D Pegu, University of the Witwatersrand

Department of Anaesthesiology, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, South Africa

FCA 1 Anaesthetic Refresher Course 2020