H2 receptor antagonists

H2 receptor antagonists compete with histamine for H2 receptors on the basolateral membrane of gastric parietal cells. Blocking this signal cuts acid secretion, both basal (including at night) and in response to food and other stimuli, so gastric juice falls in volume and acidity. Pepsin output falls along with the volume.

• FamotidineAn H2 receptor antagonist for peptic ulcers, reflux disease and acid hypersecretion, cleared mainly by the kidneys.
• CimetidineAn H2 receptor antagonist for ulcers and reflux that also inhibits liver drug metabolism and can cause gynecomastia.

• Duodenal and gastric ulcers
• Gastroesophageal reflux disease and erosive esophagitis
• Zollinger-Ellison and other acid hypersecretory states

• Confusion or delirium in older people and kidney diseaseKnown forSerious
• Headache
• Dizziness
• Constipation
• Diarrhea
• Agranulocytosis and other low blood countsSerious
• Liver injury (hepatitis, cholestatic jaundice)Serious
• Heart block and slow or fast heart rhythmsSerious
• Severe skin reactions (such as SJS/TEN)Serious

What the class has in common. Each drug's card has its own, and Known for marks what an exam expects you to know.

• Lower the dose in kidney disease: drug levels rise and confusion becomes more likely, especially in older people.
• They reduce absorption of drugs that need stomach acid, such as atazanavir, ketoconazole and dasatinib.
• Cimetidine slows the clearance of warfarin, phenytoin and theophylline; famotidine's label names only a weak CYP1A2 effect.
• Ranitidine was withdrawn in the US and suspended in the EU in 2020 because NDMA, a probable carcinogen, could build up in it.

Written for biofideX in plain words, after checking these references:

• Histamine-2 Receptor Antagonist (NCI Thesaurus)
• Famotidine for oral suspension: label (DailyMed)
• Cimetidine tablets: label (DailyMed)
• FDA requests removal of all ranitidine products (FDA)
• Ranitidine-containing medicinal products: referral (EMA)

For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.