H2 receptor antagonists

Question 1

1) Name a H2 receptor antagonist.

2) What class of drug is usually preferred to H2 receptor antagonists?

Answer 1

1) Ranitidine

2) PPIs

Question 2

Give the 2 main indications for the use of a H2 receptor antagonist.

Answer 2

1) Peptic ulcer disease: treatment and prevention of gastric and duodenal ulcers and NSAID associated ulcers.
2) GORD and dyspepsia: for relief of symptoms.

Question 3

1) How is gastric acid normally secreted?

2) How do H2 receptor antagonists work?

Answer 3

1) Acid is normally produced by the proton pump of the gastric parietal cell. Histamine is released by local paracrine cells which binds to H2 receptors on gastric parietal cells which activates the proton pump.
2) They block histamine (H2) receptors, denying activation of the proton pump and preventing acid secretion.

Question 4

1) Why can H2 antagonists not completely stop secretion of acid?
2) What are the 3 most common side effects of H2 antagonists?

Answer 4

1) Because the proton pump can be stimulated in alternate pathways.
2) GI disturbance (diarrhoea more often than constipation), headaches and dizziness.

Question 5

1) Why should the dose of H2 antagonists be reduced in patients with renal impairment?
2) Does Ranitidine have any major drug interactions?

Answer 5

1) Because H2 antagonists are excreted by the kidneys.

2) No.

Question 6

1) What is the benefit of H2 antagonists compared with PPIs?
2) Why might an anaesthetist prescribe ranitidine before a general anaesthetic?
3) When should ranitidine be taken pre-operatively?

Answer 6

1) They have a more rapid onset.
2) Used pre-operatively to mitigate the risk of gastric acid reflux causing aspiration and subsequent pneumonitis.
3) 300mg to be taken with a sip of water at least 2 hours before the start of the surgical list.