H2 Receptor Antagonists
Examples
- Ranitidine
- Famotidine
- Cimetidine (RARELY used)
Indications
- Treatment and prevention of peptic and duodenal ulcers
- Treatment of gastro-oesophageal reflux disease
- Dyspepsia and reducing risk of acid-aspiration at delivery in obstetric patients
Contraindications
Contraindications
- No specific contraindications
- May disguise symptoms of gastric cancer
- Renal impairment
- Pregnancy and breast feeding
- H2 antagonists can mask symptoms of gastric cancer, so care should be taken to rule this out if alarm symptoms present.
Mechanism
Paracrine cells in the stomach lining produce histamine in response to gastrin (stimulated by protein ingestion) or ACh (from vagal stimulation) which stimulates the parietal cells to produce gastric acid. H2-receptor antagonists block the receptors on the parietal cells thus inhibiting this action and decreasing acidity.
Administration
Usually oral but can be given IM or IV in specific rare situations.
Adverse Reactions
- Diarrhoea
- Other GI disturbance
- Dizziness
Interactions
Cimetidine inhibits the cytochrome P450 system (interacting with warfarin, etc) but ranitidine does not.
Rantidine has been shown to reduce exposure to certain antivirals, antifungals and biologics.
Education
No specific points.
Pharmacokinetics
Rapid oral absorption.
Cimetidine inhibits cytochrome P450.
Cimetidine inhibits cytochrome P450.
