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]
Famotidine was patented in 1979 and came into medical use in 1985.[6] It is available as a generic medication.[4] In 2021, it was the 57th most commonly prescribed medication in the United States, with more than 11million prescriptions.[7][8]
Famotidine has a delayed onset of action, beginning after 90 minutes. However, famotidine has a duration of effect of at least 540 minutes (9.0 h). At its peak effect, 210 minutes (3.5 h) after administration, famotidine reduces acid secretion by 7.3 mmol per 30 minutes.[20]
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, chemotherapeutics such as doxorubicin, and antifungal medications such as itraconazole. [25][26][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]
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 until 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 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.[32]
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 prescription.
Formulations of famotidine in combination with ibuprofen were marketed by Horizon Pharma under the trade name Duexis.[35]
At the start of the COVID-19 pandemic, some doctors observed that anecdotally some hospitalized patients in China may have had better outcomes on famotidine than other patients that were not taking famotidine. This led to hypotheses about use of famotidine in treatment of COVID-19.[36][37] Famotidine was considered a possible treatment for COVID-19 due to its potential anti-inflammatory effects. It was thought that famotidine could modify lung inflammation caused by coronaviruses. However, studies have shown that famotidine is not effective in reducing mortality or improving recovery in COVID-19 patients.[38] Famotidine primarily works by blocking the effects of histamine and has some potential mechanisms of action that may contribute to its anti-inflammatory properties, including the inhibition of the production of certain pro-inflammatory cytokines such as TNF-alpha and IL-6.[39][40] Another hypothesis was that famotidine might activate the vagus nerve inflammatory reflex to attenuate cytokine storm.[40] Yet another hypothesis was that famotidine can reduce the activation of mast cells and the subsequent release of inflammatory mediators, therefore acting as a mast cell stabilizer.[41][39] However, while famotidine may have some anti-inflammatory effects, there is currently insufficient evidence to support its use for treating inflammation associated with COVID-19.[38] Therefore, it is not recommended for this purpose.[42]
^Kanayama S (January 1999). "[Proton-pump inhibitors versus H2-receptor antagonists in triple therapy for Helicobacter pylori eradication]". Nihon Rinsho. Japanese Journal of Clinical Medicine. 57 (1): 153–6. PMID10036954.
^Soga T, Matsuura M, Kodama Y, Fujita T, Sekimoto I, Nishimura K, et al. (August 1999). "Is a proton pump inhibitor necessary for the treatment of lower-grade reflux esophagitis?". Journal of Gastroenterology. 34 (4): 435–40. doi:10.1007/s005350050292. PMID10452673. S2CID22115962.
^Kirika NV, Bodrug NI, Butorov IV, Butorov SI (2004). "[Efficacy of different schemes of anti-helicobacter therapy in duodenal ulcer]". Terapevticheskii Arkhiv. 76 (2): 18–22. PMID15106408.
^Jahr JS, Burckart G, Smith SS, Shapiro J, Cook DR (July 1991). "Effects of famotidine on gastric pH and residual volume in pediatric surgery". Acta Anaesthesiologica Scandinavica. 35 (5): 457–60. doi:10.1111/j.1399-6576.1991.tb03328.x. PMID1887750. S2CID44356956.
^Feldman M (May 1996). "Comparison of the effects of over-the-counter famotidine and calcium carbonate antacid on postprandial gastric acid. A randomized controlled trial". JAMA. 275 (18): 1428–1431. doi:10.1001/jama.1996.03530420056036. PMID8618369.
^Lee KW, Kayser SR, Hongo RH, Tseng ZH, Scheinman MM (May 2004). "Famotidine and long QT syndrome". The American Journal of Cardiology. 93 (10): 1325–1327. doi:10.1016/j.amjcard.2004.02.025. PMID15135720.
^Hegazy SK, El-Haggar SM, Alhassanin SA, El-Berri EI (January 2021). "Comparative randomized trial evaluating the effect of proton pump inhibitor versus histamine 2 receptor antagonist as an adjuvant therapy in diffuse large B-cell lymphoma". Medical Oncology. 38 (1): 4. doi:10.1007/s12032-020-01452-z. PMID33394214. S2CID230485193.
^Lim SG, Sawyerr AM, Hudson M, Sercombe J, Pounder RE (June 1993). "Short report: the absorption of fluconazole and itraconazole under conditions of low intragastric acidity". Alimentary Pharmacology & Therapeutics. 7 (3): 317–321. doi:10.1111/j.1365-2036.1993.tb00103.x. PMID8117350. S2CID20462864.
^US patent 4283408, Yasufumi Hirata, Isao Yanagisawa, Yoshio Ishii, Shinichi Tsukamoto, Noriki Ito, Yasuo Isomura and Masaaki Takeda, "Guanidinothiazole compounds, process for preparation and gastric inhibiting compositions containing them", issued 11 August 1981
^"Sankyo Pharma". Skyscape Mediwire. 2002. Archived from the original on 23 February 2009. Retrieved 31 October 2009.
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