Famotidine  

Famotidine
Systematic (IUPAC) name
3-([2-(diaminomethyleneamino)thiazol- 4-yl]methylthio)- N'-sulfamoylpropanimidamide
Identifiers
CAS number	76824-35-6
ATC code	A02BA03
PubChem	3325
DrugBank	APRD00296
ChemSpider	3208
Chemical data
Formula	C8H15N7O2S3
Mol. mass	337.449 g/mol
Pharmacokinetic data
Bioavailability	2066%
Protein binding	1028%
Metabolism	hepatic-less than 30%
Half life	2.54 hours (clinical half-life 812 hours)
Excretion	Principally excreted unchanged in urine
Therapeutic considerations
Licence data	US FDA:link
Pregnancy cat.	B1 (Au), B (U.S.)
Legal status	S3/S4 (Au), POM/OTC (UK), OTC/-only (U.S.)
Routes	Oral, IV
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Famotidine (INN) (pronounced /fmtdin/) is a histamine H₂-receptor antagonist that inhibits stomach acid production, and it is commonly used in the treatment of peptic ulcer disease (PUD) and gastroesophageal reflux disease (GERD/GORD). It is commonly marketed by Johnson & Johnson/Merck under the trade names Pepcidine and Pepcid. 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.^[1]

History and development

Famotidine was developed 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 30 times more active than cimetidine.^{[citation needed]}

It was first marketed in 1985. Pepcid RPD orally-disintegrating tablets (that are not swallowed) were released in 1999. Generic preparations became available in 2001, e.g. Fluxid (Schwarz) or Quamatel (Gedeon Richter Ltd.).

In the United States, a product called Pepcid Complete is available that combines famotidine with an antacid in a chewable tablet to ameliorate the relatively slow onset of effects. In the UK, this product is known as Pepcidtwo.

Famotidine suffers from poor bioavailability (50%), as famotidine is poorly soluble in acid pH e.g. stomach. Famotidine used in combination with antacids promotes local delivery of these drugs to the receptor of the parietal cell wall. Therefore researchers are developing innovative formulations of tablets, such gastroretentive drug delivery systems. Such tablets are retained in the stomach for a longer period of time and thereby improve the bioavailability of drugs. Local delivery also increases bioavailability at the stomach wall receptor site and increases the efficacy of drugs to reduce acid secretion.^[2]

Clinical use

Certain preparations of famotidine are available over the counter (OTC) in various countries. In the United States, preparations of 10 mg and 20 mg tablets, sometimes in combination with a more traditional antacid, are available OTC. Larger doses still require a prescription.

Famotidine is given to surgery patients before operations to prevent post-operation nausea and to reduce the risk of aspiration pneumonitis.

Adverse effects

Adverse drug reactions are associated with famotidine use. In clinical trials, the most common adverse effects were headache, dizziness, and constipation or diarrhea.^[3]

References

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