|Trade names||Pepcid, others|
|By mouth (tablets), intravenous|
|Bioavailability||40–45% (by mouth)|
|Elimination half-life||2.5–3.5 hours|
|Excretion||Kidney (25–30% unchanged [Oral])|
|CompTox Dashboard (EPA)|
|Chemical and physical data|
|Molar mass||337.44 g·mol−1|
|3D model (JSmol)|
Famotidine, sold under the brand name Pepcid among others, is a histamine H2 receptor antagonist medication that decreases stomach acid production. It is used to treat peptic ulcer disease, gastroesophageal reflux disease, and Zollinger-Ellison syndrome. It is taken by mouth or by injection into a vein. It begins working within an hour.
Common side effects include headache, intestinal upset, and dizziness. Serious side effects may include pneumonia and seizures. Use in pregnancy appears safe but has not been well studied while use during breastfeeding is not recommended. It is a histamine H2 receptor antagonist.
Famotidine was patented in 1979 and came into medical use in 1985. It is available as a generic medication. In 2019, it was the 104th most commonly prescribed medication in the United States, with more than 6 million prescriptions.
- Relief of heartburn, acid indigestion, and sour stomach
- Treatment for gastric and duodenal ulcers
- Treatment for pathologic gastrointestinal hypersecretory conditions such as Zollinger–Ellison syndrome and multiple endocrine adenomas
- Treatment for gastroesophageal reflux disease (GERD)
- Treatment for esophagitis
- Part of a multidrug regimen for Helicobacter pylori eradication, although omeprazole may be somewhat more effective.
- Prevention of NSAID-induced peptic ulcers.
- Given to surgery patients before operations to reduce the risk of aspiration pneumonitis.
Mechanism of action
Activation of H2 receptors located on parietal cells stimulates proton pumps to secrete acid into the stomach lumen. Famotidine, an H2 antagonist, blocks the action of histamine on the parietal cells, ultimately reducing acid secretion into the stomach.
Unlike cimetidine, the first H2 antagonist, famotidine has a minimal effect on the cytochrome P450 enzyme system, and does not appear to interact with as many drugs as other medications in its class. Some exceptions include antiretrovirals such as atazanavir and chemotherapeutics such as doxorubicin 
Famotidine was developed by Yamanouchi Pharmaceutical Co. It was licensed in the mid-1980s by Merck & Co. and is marketed by a joint venture between Merck and Johnson & Johnson. The imidazole ring of cimetidine was replaced with a 2-guanidinothiazole ring. Famotidine proved to be nine times more potent than ranitidine, and thirty-two times more potent than cimetidine.
In the United States and Canada, a product called Pepcid Complete, which combines famotidine with an antacid in a chewable tablet to quickly relieve the symptoms of excess stomach acid, is available. In the UK, this product was known as Pepcidtwo prior to its discontinuation in April 2015.
Famotidine has poor bioavailibility (50%) due to low gastroretention time. Famotidine is less soluble at higher pH, and when used in combination with antacids gastroretention time is increased. This promotes local delivery of these drugs to receptors in the parietal cell membrane and increases bioavailibility. Researchers are developing tablet formulations that rely on other gastroretentive drug delivery systems such as floating tablets to further increase bioavailibility.
Certain preparations of famotidine are available over the counter (OTC) in various countries. In the United States and Canada, 10 mg and 20 mg tablets, sometimes in combination with an antacid, are available OTC. Larger doses still require a medical prescription.
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|Wikimedia Commons has media related to Famotidine.|
- "Famotidine". Drug Information Portal. U.S. National Library of Medicine.