H2 Antagonist

Question 1

Example of a H2 antagonist

Answer 1

Ranitidine

Question 2

How do H2 antagonists work?

Answer 2

Histamine H2 receptor blockers reduce gastric acid secretion.

Acid is normally produced by the proton pump of the gastric parietal cell, which secretes H+ into the stomach lumen in exchange for K+ into the cell.
The proton pump is regulated by histamine and other things.

Histamine is released by nearby paracrine cells and binds to H2 receptors on the gastric parietal cell. Via a second messenger system, this activates the proton pump. Blocking the H2 receptor therefore reduces acid secretion.

However, as the proton pump can be stimulated by other pathways, H2 blockers cannot completely suppress gastric acid production. In this respect they differ from PPIs, which tend to have a more complete suppressible effect.

Question 3

Indications of H2 anatgonists

Answer 3

Peptic ulcer disease: treatment and prevention of gastric and duodenal ulcers and NSAID-associated ulcers, although PPIs are more effective and usually preferred.

GORD and Dyspepsia: for relief of symptoms. PPIs are the main alternative and are preferred in severe cases.

Question 4

Contraindications of H2 anatgonists

Answer 4

H2 blockers are excreted by the kidneys, so their dose should be reduced in renal impairment.

Like PPIs, they can disguise the symptoms of gastric cancer so it is important not just to treat symptoms without considering, and if appropriate, investigating their cause.

Question 5

Side effects of H2 anatgonists

Answer 5

Well tolerated with few side effects

Most common among these are bowel disturbances (diarrhoea, or less often, constipation), headache and dizziness

Question 6

Possible interactions of H2 anatgonists

Answer 6

No major drug interactions

Question 7

Elimination

Answer 7

Renal

Question 8

Patient information

Answer 8

May be purchased over the counter, but only for short term use. Prescription needed for more than 2 weeks.

150mg twice daily is the typical dose though this may vary, as does the duration of therapy.
Oral preparations can be taken before, with or after food. (these are more expensive than tablets)

Explain treatment is to reduce stomach acid and will hopefully improve symptoms and allow their ulcer to heal.
Ensure patient is aware of the duration of the therapy. Inform patient to report any red flag symptoms (weightloss, swallowing difficulty) if they arise.

For treatment of peptic ulcer disease, repeat endoscopy may be necessary in some cases to confirm healing.
For symptomatic treatment of dyspepsia and GORD, the patients symptoms are the best guide to effect of therapy