An H₂-receptor antagonist, often shortened to H₂-antagonist, is a drug used to block the action of histamine on parietal cells in the stomach, decreasing acid production by these cells. These drugs are used in the treatment of dyspepsia, however their use has waned since the advent of the more effective proton pump inhibitors.

Like the H₁-antihistamines, the H₂-antagonists are inverse agonists rather than true receptor antagonists.

Clinical use of antihistamines

Indications

H₂-antagonists are clinically used in the treatment of acid-related gastrointestinal conditions. Specifically, these indications may include: (Rossi, 2004)

• peptic ulcer disease (PUD)
• gastroesophageal reflux disease (GERD)
• dyspepsia

Adverse drug reactions

H₂-antagonists are generally well-tolerated, except for cimetidine where all of the following adverse drug reactions (ADRs) are common. Infrequent ADRs include hypotension. Rare ADRs include: headache, tiredness, dizziness, confusion, diarrhoea, constipation, and rash. (Rossi, 2004)

Examples

Cimetidine was the prototypical member of the H₂-antagonists. Further developments, using quantitative structure-activity relationships (QSAR) led to the development of further agents with improved tolerability-profiles. In the United States, all four members of the group are available over the counter in relatively low doses, and have become extremely popular medications marketed to heartburn sufferers.

• cimetidine
• ranitidine
• famotidine
• nizatidine

Reference

• Rossi S (Ed.) (2004). Australian Medicines Handbook 2004. Adelaide: Australian Medicines Handbook. ISBN 0-9578521-4-2