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. 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 until 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. Society and culture 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. Formulations of famotidine in combination with ibuprofen were marketed by Horizon Pharma under the trade name Duexis. Research COVID-19 At the start of the COVID-19 pandemic, some doctors observed that anecdotally some hospitalized patients on famotidine in China may have had better outcomes than other patients that were not taking famotidine. This led to hypotheses about use of famotidine in treatment of COVID-19. Famotidine was researched for potential benefit in treating COVID-19 following hypotheses at the start of the pandemic that it may be an applicable medication. No good evidence of benefit was found. Veterinary uses Famotidine is given to dogs and cats with acid reflux. Famotidine has been used in combination with an H1 antagonist to treat and prevent urticaria caused by an acute allergic reaction. References External links Amidines Guanidines H2 receptor antagonists Sulfamides Thiazoles Thioethers Wikipedia medicine articles ready to translate