H2 receptor antagonists

Question 1

Name examples of H2 receptor antagonists.

Answer 1

Cimetidine, ranitidine, famotidine, nizatidine.

Question 2

What are the indications of H2 receptor antagonists?

Answer 2

benign duodenal/gastric ulceration, maintenance treatment of duodenal ulceration (famotidine), NSAID-associated ulceration, reflux oesophagitis, prophylaxis of stress ulceration (cimetidine, ranitidine), prophylaxis of NSAID-associated duodenal/gastric ulcer (ranitidine), gastric acid reduction/prophylaxis in obstetrics (cimetidine, ranitidine), gastric acid reduction/prophylaxis during surgical procedures (cimetidine, ranitidine), short-bowel syndrome (cimetidine), to reduce degradation of pancreatic acid supplements (cimetidine), GORD, chronic episodic dyspepsia (ranitidine), when gastric acidity needs to be reduced but oral route not available (ranitidine).

Question 3

What is the mechanism of action of H2 receptor antagonists?

Answer 3

H2 receptor antagonists competitively inhibit the actions of histamine at H2 receptors on parietal cells. This prevents the activation of adenylate cyclase leading to a reduction in cAMP. The lowered concentration of cAMP leads to a reduction in protein kinase activity and therefore a reduction in proton pump activity, resulting in a decrease in acid secretion into the stomach. This reduced acid secretion promotes healing of gastric and duodenal ulcers as well as reducing symptoms of GORD.

Question 4

What are the very common/common unwanted side effects of H2 receptor antagonists?

Answer 4

constipation (famotidine), diarrhoea, dizziness, headache, malaise (cimetidine), sweating (nizatidine).

Question 5

What is the patient/carer advice for ranitidine?

Answer 5

In fat malabsorption syndrome, give oral doses 1-2 hours before food to enhance the effects of pancreatic enzyme replacement.