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Dyspepsia - unidentified cause - Management
What issues should I consider before prescribing an H2-receptor antagonist?
- Gastric malignancy should be excluded prior to initiation of therapy with a H2-receptor antagonist (H2RA). Symptomatic response to H2RA therapy does not preclude the presence of gastric malignancy.
- Stop or do not initiate H2RA at least 14 days before endoscopy, as they may mask gastric cancer.
- Four H2RAs are available in the UK: cimetidine, famotidine, nizatidine, and ranitidine. Licensed indications differs between H2RAs for the management of dyspepsia:
- All four H2RAs are licensed for the treatment and symptomatic relief of gastro-oesphageal reflux disease.
- However, only cimetidine and ranitidine are both licensed for persistent symptoms of dyspepsia with or without ulceration (including meal-related upper abdominal pain).
- Choice of H2RA:
- Famotidine, nizatidine and ranitidine may be considered (see Table 1 for indications and dosage). Of these, ranitidine is preferred because it is also licensed for persistent symptoms of dyspepsia and is considerably cheaper than famotidine and nizatidine.
- Cimetidine is less preferred, given the higher risk of drug interaction with this drug (inhibition of the cytochrome P450 enzymes). The other three H2RAs do not share the drug metabolism inhibitory properties of cimetidine [BNF 55, 2008].
- Availability over the counter:
- Only famotidine and ranitidine are available over-the-counter, and both are licensed for the relief of heartburn, indigestion, and hyperacidity.
- Proprietary and generic versions of ranitidine 75 mg tablets are widely available.
- Proprietary famotidine is available as 10 mg tablets (alone or in combination with antacids).
- Drug interactions:
- Cimetidine should be avoided by people taking erythromycin, warfarin, amiodarone, theophylline, carbamazepine, phenytoin, or sodium valproate; cimetidine inhibits hepatic drug metabolism by binding to microsomal cytochrome P450.
- Due to the decreased intragastric acidity, the absorption of ketoconazole or itraconazole may be reduced during H2RA treatment.
- Adverse effects are uncommon and include diarrhoea, headache, dizziness, rash, and tiredness.
Table 1. Licensed doses of H2-receptor antagonists.
H2-receptor antagonist | Persistent symptoms of dyspepsia | Gastro-oesophageal reflux disease. |
|---|
Ranitidine | For chronic episodic dyspepsia: 150 mg twice daily for up to 6 weeks. | Symptomatic relief: a dose regimen of 150 mg twice daily for 2 weeks. This can be repeated in those in whom the initial symptomatic response is inadequate. |
Famotidine | — | Symptomatic relief: 20 mg twice daily, given for six to twelve weeks. Maintenance therapy: 20 mg twice daily. |
Nizatidine | — | Dose: 150 mg twice daily, up to 300 mg twice daily. Therapy for up to 12 weeks is indicated for erosions and ulcerations, and associated heartburn. |
|
[ABPI Medicines Compendium, 2003; ABPI Medicines Compendium, 2005; ABPI Medicines Compendium, 2009; ABPI Medicines Compendium, 2008c]
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