Cimetidine
An H2 receptor antagonist for ulcers and reflux that also inhibits liver drug metabolism and can cause gynecomastia.
Drug card
- How it works
- Blocking histamine H2 receptors on parietal cells to reduce acid secretion
- Used for
- Duodenal and benign gastric ulcers
- Erosive gastroesophageal reflux disease
- Zollinger-Ellison syndrome and other hypersecretory states
- Known for
- Breast enlargement in men (gynecomastia)
- 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 cimetidine work?
A competitive H2 receptor antagonist that cuts daytime and nighttime basal acid and acid driven by food, histamine, caffeine and insulin. It also inhibits liver microsomal enzymes, slowing the clearance of warfarin, phenytoin, theophylline, lidocaine and other drugs, and it has a weak antiandrogenic effect.
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 cimetidine used for?
- Duodenal and benign gastric ulcers
- Erosive gastroesophageal reflux disease
- Zollinger-Ellison syndrome and other hypersecretory states
Side effects
Side effects of cimetidine
- Breast enlargement in men (gynecomastia)Known for
- Headache
- Dizziness and drowsiness
- Diarrhea
- Reversible confusion, mainly in the severely illSerious
- Impotence with long, high-dose use
- Agranulocytosis and low plateletsSerious
- Liver injury, mostly cholestaticSerious
- Interstitial nephritisSerious
- PancreatitisSerious
- Slow heart rate and heart blockSerious
- Severe skin reactions (such as SJS/TEN)Serious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- It slows the metabolism of warfarin, phenytoin, theophylline and lidocaine: monitor prothrombin time and drug levels.
- Confusion is likelier from age 50 and with liver or kidney disease.
- It lowers ketoconazole absorption; give ketoconazole at least 2 hours before cimetidine.
- Rapid intravenous bolus injection has caused arrhythmias and low blood pressure.
Remember it
A way to remember it
Cimetidine gets in the way of three things: H2 receptors, liver enzymes and androgens.
It blocks H2 receptors (less acid), inhibits the liver enzymes that clear warfarin, phenytoin and theophylline, and has a weak antiandrogenic effect that can cause gynecomastia.
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
Cimetidine is one of 15 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
Start Practicing