UNDER REVIEW (September 2016)
Mechanism of Action:
Ranitidine is a histamine H2-receptor antagonist. Histamine, released from enterochromaffin (mast-like) cells in the stomach, activates histamine H2 receptors (seven-transmembrane G-protein-coupled receptors) which promote acid secretion. Being a reversible competitor of histamine at H2 receptors on parietal cells, ranitidine prevents histamine-induced gastric acid secretion. It also indirectly inhibits gastrin- and acetylcholine-stimulated gastric acid secretion, which also results in reduced secretion of pepsin (digestive enzyme that hydrolyzes protein).
Lecture and CAL materials:
Drug specifics
| Alternative drug name | Zantac ® |
| Effects | Indicated for treating peptic ulcers and gastroesophageal reflux disease. It reduces gastric acid secretion (basal and food induced) and levels of pepsin (which may contribute to formation of ulcers). Thus, it aids healing of gastric and duodenal ulcers and eases symptoms of heartburn. Ranitidine may also be prescribed together with antibacterials to treat helicobacter pylori infection, which is often the cause of gastric ulcers. |
| Adverse actions | Fairly well tolerated but may cause diarrhoea, dizziness, changes in liver function tests. |
| Dose | Oral tablets once or twice per day. |
| Interactions | Caution in patients with renal or hepatic impairment – disrupts elimination of drug. Ranitidine is not known to be dangerous in pregnancy. |
| Contraindications | not specified |
| Comments | OTHER H2-ANTAGONISTS. The first available was cimetidine which is well known for preventing the metabolism of other drugs (e.g. warfarin, phenytoin) by its inhibitory action on cytochrome P450 and also causes gynaecomastia and rarely heart block. Newer H2-receptor antagonists include nizatidine and famotidine. The use of this class has reduced significantly following the advent of proton pump inhibitors (e.g. omeprazole) which are more powerful at suppressing acid production. |
| Contributors |
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