Famotidine
An H2 receptor antagonist for peptic ulcers, reflux disease and acid hypersecretion, cleared mainly by the kidneys.
Drug card
- How it works
- Blocking histamine H2 receptors on parietal cells to reduce acid secretion
- Used for
- Duodenal and gastric ulcers
- Gastroesophageal reflux disease and erosive esophagitis
- Zollinger-Ellison and other hypersecretory states
- Known for
- Confusion, delirium or hallucinations
- Its name
- -tidine means an H2 receptor antagonist
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does famotidine work?
A competitive blocker of H2 receptors on parietal cells that lowers basal, nighttime and stimulated acid, reducing both the volume and the acidity of gastric juice. About two-thirds of it is cleared by the kidneys, so levels rise in kidney disease. It is a weak CYP1A2 inhibitor, which matters mainly for tizanidine.
Like other 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.
Uses
What is famotidine used for?
- Duodenal and gastric ulcers
- Gastroesophageal reflux disease and erosive esophagitis
- Zollinger-Ellison and other hypersecretory states
Side effects
Side effects of famotidine
- Confusion, delirium or hallucinationsKnown forSerious
- Headache
- Dizziness
- Constipation
- Diarrhea
- Seizures, mainly with kidney diseaseSerious
- QT prolongationSerious
- Agranulocytosis and pancytopeniaSerious
- Liver injury (hepatitis, cholestatic jaundice)Serious
- RhabdomyolysisSerious
- Severe skin reactions (such as SJS/TEN)Serious
- Anaphylaxis and angioedemaSerious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Reduce the dose in moderate or severe kidney disease, where confusion, seizures and other CNS effects are more likely.
- Avoid with tizanidine, whose levels it can raise, causing low blood pressure, slow pulse or heavy drowsiness.
- It lowers absorption of drugs that need acid; avoid with dasatinib, delavirdine, cefditoren and fosamprenavir.
Remember it
A way to remember it
Histamine knocks on the parietal cell's H2 door; H2 blockers jam the lock, so less acid flows.
H2 receptor antagonists compete with histamine at the H2 receptors of gastric parietal cells, so the cells secrete less acid.
Written for biofideX
Its name
-tidine means H2 receptor antagonist
Famotidine and cimetidine block histamine H2 receptors on stomach parietal cells, cutting acid. Pethidine, an opioid, and azacitidine, an anticancer drug, end in -tidine by chance.
- Every drug name stem
Its class
H2 receptor antagonists
Other H2 receptor antagonists with a card:
Easily mixed up with proton pump inhibitors and second-generation antihistamines.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
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.
Stomach and gut
Famotidine is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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