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Trade namesPepcid, others
  • 3-[({2-[(diaminomethylidene)amino]-1,3-thiazol-4-yl}methyl)sulfanyl]-N-sulfamoylpropanimidamide
Clinical data
  • AU: B1
  • US: B (No risk in non-human studies)
Routes of
By mouth (tablets), Intravenous
Defined daily dose40 mg[1]
External links
License data
Legal status
Bioavailability40–45% (by mouth)[2]
Protein binding15–20%[2]
Elimination half-life2.5–3.5 hours[2]
ExcretionKidney (25–30% unchanged [Oral])[2]
Chemical and physical data
Molar mass337.44 g·mol−1
3D model (JSmol)
  • NS(=O)(=O)/N=C(\N)CCSCc1csc(n1)N=C(N)N
  • InChI=1S/C8H15N7O2S3/c9-6(15-20(12,16)17)1-2-18-3-5-4-19-8(13-5)14-7(10)11/h4H,1-3H2,(H2,9,15)(H2,12,16,17)(H4,10,11,13,14) checkY

Famotidine, sold under the brand name Pepcid among others, is a medication that decreases stomach acid production.[3] It is used to treat peptic ulcer disease, gastroesophageal reflux disease, and Zollinger-Ellison syndrome.[3] It is taken by mouth or by injection into a vein.[3] It begins working within an hour.[3]

Common side effects include headache, intestinal upset, and dizziness.[3] Serious side effects may include pneumonia and seizures.[3][4] Use in pregnancy appears safe but has not been well studied while use during breastfeeding is not recommended.[5] It is a histamine H2 receptor antagonist.[3]

Famotidine was patented in 1979 and came into medical use in 1985.[6] It is available as a generic medication.[4] A month supply in the United Kingdom costs the NHS about £30 as of 2019.[4] In the United States the wholesale cost of this amount is about $2.[7] In 2017, it was the 115th most commonly prescribed medication in the United States, with more than six million prescriptions.[8][9]

Medical uses

Famotidine is also given to dogs and cats with acid reflux.[21] Famotidine has been used in combination with an H1 antagonist to treat and prevent urticaria caused by an acute allergic reaction.[22]


The defined daily dose is 40 mg by mouth or by injection.[1] For adults for GERD 20 mg twice per day by mouth for six weeks may be used.[3] For esophagitis doses of up to 40 mg twice per day for 3 months may be used.[3]

Side effects

The most common side effects associated with famotidine use include headache, dizziness, and constipation or diarrhea.[23][24]

Famotidine may contribute to QT prolongation,[25] particularly when used with other QT-elongating drugs, or in people with poor kidney function.[26]

Mechanism of action

Activation of H2 receptors located on parietal cells stimulates the proton pump to secrete acid. Famotidine (H2 antagonist) blocks the action of histamine in the parietal cells, ultimately blocking acid secretion in the stomach.


Unlike cimetidine, the first H2 antagonist, famotidine has no effect on the cytochrome P450 enzyme system, and does not appear to interact with other drugs.[27]


Famotidine was developed by Yamanouchi Pharmaceutical Co.[28] It was licensed in the mid-1980s by Merck & Co.[29] 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.[30]

It was first marketed in 1981. Pepcid RPD orally disintegrating tablets were released in 1999. Generic preparations became available in 2001, e.g. Fluxid (Schwarz) or Quamatel (Gedeon Richter Ltd.).

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.[31]

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 wall and increases bioavailibility. Researchers are developing tablet formulations that rely on other gastroretentive drug delivery systems such as floating tablets to further increase bioavailibility.[32]


It is taken by mouth, as a tablet or suspension, or by injection into a vein.[3]

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,[33][34] are available OTC. Larger doses still require a medical prescription.

Formulations of famotidine in combination with ibuprofen were marketed by Horizon Pharma under the trade name Duexis.[35]

Society and culture


A month supply in the United Kingdom costs the NHS about £30 as of 2019.[4] In the United States the wholesale cost of this amount is about $2.[7] In 2017, it was the 115th most commonly prescribed medication in the United States, with more than six million prescriptions.[8][9]


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  33. Pepcid Complete
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External links

External sites: