|Systematic (IUPAC) name|
|3-([2-(diaminomethyleneamino)thiazol- 4-yl]methylthio)- N'-sulfamoylpropanimidamide|
|Licence data||US FDA:|
|Routes||Oral (tablet form)|
|Excretion||Renal (25-30% unchanged [Oral])|
|Mol. mass||337.449 g/mol|
|(what is this?)|
Famotidine (INN) // 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 and by Astellas under the trade name Gaster. 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.
Certain preparations of famotidine are available over the counter (OTC) in various countries. In the US 20 or more mg, 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 postoperative nausea and to reduce the risk of aspiration pneumonitis. Famotidine is also given to some patients taking NSAIDs, to prevent peptic ulcers. It serves as an alternative to proton-pump inhibitors.
It is also given to dogs and cats with acid reflux.
Side-effects are associated with famotidine use. In clinical trials, the most common adverse effects were headache, dizziness, and constipation or diarrhea. Antacid preparations such as famotidine, by suppressing acid-mediated breakdown of proteins, lead to an elevated risk of developing food or drug allergies. This happens due to undigested proteins then passing into the gastrointestinal tract where sensitization occurs. It is unclear whether this risk occurs with only long-term use or with short-term use as well.
Famotidine was developed by Yamanouchi Pharmaceutical Co. It was licensed in the mid-80s 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.
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 is known as Pepcidtwo.
Famotidine suffers from poor bioavailability (50%), as it is poorly soluble in the low pH of the 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 as gastroretentive drug delivery systems. Such tablets are retained in the stomach for a longer period of time, thereby improving 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.
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