Famotidine

Reference

http://www.rxlist.com/pepcid-drug/clinical-pharmacology.htm https://en.wikipedia.org/wiki/Famotidine

Manufacturing Process

60.0 kg of dichloroacetone is dissolved in 550 ml of acetone. After cooling the solution to -5°C, 55.8 kg of amidinothiourea is added to the solution under cooling portionwise at one hour intervals in a 10 kg amount of amidinothiourea. The mixture is stirred continuously for 5 days below 0°C. The 111.6 kg resultant precipitates of N"-[4-(chloromethyl)-4,5-dihydro-4- hydroxy-2-thiazolyl]-guanidine hydrochloride are collected, and washed with 50 L of acetone. In 500 ml of water are dissolved 111.6 kg of N"-[4- (chloromethyl)-4,5-dihydro-4-hydroxy-2-thiazolyl]-guanidine hydrochloride and 32.9 kg of thiourea. The solution is stirred for one hour at 50°C. N'-[4- [[(Aminoiminomethyl)thio]methyl]-2-thiazolyl]-guanidine dihydrochloride is formed in the reaction mixture, and this reaction mixture containing this compound is directly used for the next process without isolation of the formed compound.The reaction mixture obtained is cooled below 10°C, and to the solution are added 45.6 kg of beta-chloropropionitrile and 200 L of isopropanol. A solution of 69.1 kg of sodium hydroxide in 280 L of water is added dropwise to the solution under nitrogen stream followed by stirring for 2 hours at 0°C. The crystals precipitated are collected by filtration, and washed with cold water and dried to provide 91.7 kg of the N"-[4-[[(2-cyanoethyl)thio]methyl]-2- thiazolyl]-guanidine, melting point 125-126.5°C.In 60 L of anhydrous dimethylformamide is dissolved 34.3 kg of the N"-[4- [[(2-cyanoethyl)thio]methyl]-2-thiazolyl]-guanidine. After adding 60 L of anhydrous methanol to the solution, 61.9 kg of hydrogen chloride gas is passed through the solution below 5°C. After stirring the reaction mixture for 2 days at 0°C, the reaction mixture is poured into a mixture of 350 L of water, 250 kg of potassium carbonate, 30 L of ethyl acetate and ice while stirring below 5°C for 2 hours. The resultant precipitates are collected by filtration. After stirring a mixture of the precipitates and 400 L of water for 0.5 hour at 0°, the resultant precipitates are collected by filtration, washed with 40 L of water and 10 L of cooled acetone respectively, and dried at reduced pressure to provide 30.6 kg of the methyl 3-[[[2-[(diaminomethylene)amino]-4- thiazolyl]methyl]thio]propionimidate showing a melting point of 125.7°C.In 340 L of methanol is dissolved 88.4 kg of sulfamide under heating, and the solution is cooled to 30°C. To the solution, 114.2 kg of the methyl 3-[[[2- [(diaminomethylene)amino]-4-thiazolyl]methyl]thio]propionimidate are added portionwise three times while stirring at 20-30°C. (The second addition is added 8 hours after the first addition, and the third addition is added 24 hours after the first addition). After stirring the reaction mixture for a further 2 days, the crystals formed are collected by filtration, washed with 200 L of cooled methanol, and air-dried at room temperature to provide 87.5 kg of the 3-[[[2-[(diaminomethylene)amino]-4-thiazolyl]methyl]thio]-Nsulfamoylpropionamidine (generic name: famotidine) showing a melting point of 157.6°C. Some of the obtained product is recrystallized from dimethylformamide-water, and is dissolved in an equivalent molar amount of aqueous acetic acid (%). To the solution is added an equivalent molar amount of a dilute sodium hydroxide solution in water to separate crystals showing a melting point of 163-164°C.

Therapeutic Function

Antiulcer

Contact allergens

Contact dermatitis in a nurse from famotidine, an H2-receptor agonist, was described. In industry, three cases were reported due to intermediates of the synthesis of 2-diamino-ethylene-amino-thiazolyl-methylenethio urea-dichloride, and 4-chloromethyl-2-guanidinothiaz ole-nitrochloride.

Biochem/physiol Actions

H2 histamine receptor antagonist; anti-ulcer agent

Synthesis

Famotidine, 3-[[[2-[(aminomethyl)amino]-4-thiazolyl] methyl]thio]- N-(aminosulfonyl)propanimidamide (16.2.13), is synthesized from S-(2-aminothiazol-4-ylmethyl) isothiourea (16.2.9), which is synthesized by reacting 1,3-dichloroacetone with two molecules of thiourea, during which a thiazol ring is formed and the chlorine atom is substituted, giving an intermediate 2-amino-5-chlormethylthiazol. Reacting this with 2-chlorpropionitrile gives S-(2-aminothiazol-4-yl-methyl)-2-cyanoethane (16.2.10), which in turn is reacted with benzoylizthiocyanate. The resulting benzoylthiourea derivative (16.2.11) first undergoes S-methylation by methyliodide and further cleaved by ammonia into 3-[[[2- (aminomethyl)amino]-4-thiazolyl]-methyl]thio]ethylcyanide (16.2.12). Successive methanolysis of the nitrile group and subsequent reaction of the resulting iminoether with sulfonamide gives famotidine (16.2.13).

Veterinary Drugs and Treatments

In veterinary medicine, famotidine may be useful for the treatment and/or prophylaxis of gastric, abomasal and duodenal ulcers, uremic gastritis, stress-related or drug-induced erosive gastritis, esophagitis, duodenal gastric reflux, and esophageal reflux. Famotidine has fewer drug interactions and activity may persist longer than cimetidine.

Drug interactions

Potentially hazardous interactions with other drugs Antifungals: absorption of itraconazole and ketoconazole reduced; concentration of posaconazole possibly reduced - avoid with suspension. Antivirals: concentration of atazanavir reduced - adjust doses of both drugs; concentration of raltegravir possibly increased - avoid; avoid for 12 hours before and 4 hours after rilpivirine. Ciclosporin: possibly increased ciclosporin levels. Cytotoxics: possibly reduced dasatinib concentration - avoid if possible; avoid with erlotinib; possibly reduced absorption of pazopanib - give at least 2 hours before or 10 hours after famotidine; possibly reduced absorption of lapatinib. Ulipristal: contraceptive effect possibly reduced - avoid with high dose ulipristal.

Metabolism

Metabolism of famotidine occurs in the liver, with formation of an inactive metabolite, the sulfoxide. Following oral administration, the mean urinary excretion of famotidine is 65-70% of the absorbed dose, 25-30% as unchanged compound. Renal clearance is 250-450 mL/min, indicating some tubular excretion. A small amount may be excreted as the sulfoxide.

Brand name

Fluxid (Schwarz Pharma); Pepcid (Merck);Amifatidine;Famodil;Pepsidac;GASTER.

General Description

Famotidine is a histamine H2-receptor antagonist, which promotes the healing of erosive esophagitis, gastric and duodenal ulcers since it inhibits the gastric acid secretion in humans.Pharmaceutical secondary standards for application in quality control, provide pharma laboratories and manufacturers with a convenient and cost-effective alternative to the preparation of in-house working standards.