H2-receptor antagonist
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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.
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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.
Reference
- Rossi S (Ed.) (2004). Australian Medicines Handbook 2004. Adelaide: Australian Medicines Handbook. ISBN 0-9578521-4-2pt:Antihistaminico H2