Can famotidine (H2 blocker) cause diarrhea?

Can Famotidine Cause Diarrhea?

Yes, famotidine can cause diarrhea as a side effect, although it is relatively uncommon compared to other gastrointestinal medications.

Mechanism and Incidence

• Famotidine is a histamine H2-receptor antagonist (H2RA) that works by inhibiting gastric acid secretion 1, 2
• Unlike proton pump inhibitors (PPIs), famotidine is metabolized differently and does not significantly interact with the cytochrome P-450 system, particularly CYP2C19 1
• Famotidine is considered to have a favorable safety profile compared to other acid-reducing medications 2, 3

Evidence Regarding Diarrhea as a Side Effect

• Clinical guidelines mention diarrhea as a potential side effect of famotidine, though it is not among the most commonly reported adverse effects 1
• In contrast to some medications used for gastrointestinal conditions, famotidine is sometimes used therapeutically to help manage certain types of chronic diarrhea, particularly in specific patient populations 1
• The FAMOUS trial, which studied famotidine for prevention of peptic ulcers in patients taking low-dose aspirin, did not report diarrhea as a significant adverse event 1, 4

Comparison with Other Acid-Reducing Medications

• Famotidine has fewer drug interactions than other H2 blockers like cimetidine, which more strongly inhibits the cytochrome P-450 system 1
• Unlike some proton pump inhibitors which have been associated with higher rates of diarrhea, famotidine tends to have a lower incidence of this side effect 1
• When comparing H2 blockers to PPIs for patients on antiplatelet therapy, guidelines note that H2 blockers like famotidine may be considered as alternatives to PPIs, suggesting a generally favorable side effect profile 1

Patient-Specific Considerations

• In patients with chronic gastritis, famotidine (20 mg/day) has been shown to attenuate abdominal symptoms without significant reports of diarrhea as an adverse effect 5
• For pediatric patients, famotidine has been used safely at doses of 0.5 mg/kg twice daily without notable diarrheal side effects 6
• In patients with mastocytosis, famotidine is recommended to manage gastric hypersecretion with minimal gastrointestinal side effects 1

Management if Diarrhea Occurs

• If diarrhea develops while taking famotidine, consider:
  • Evaluating for other causes of diarrhea 1
  • Potentially reducing the dose if symptoms are mild 1
  • Switching to another H2 blocker or different class of acid-reducing medication if symptoms persist 1
  • Ensuring adequate hydration to prevent dehydration 1

Clinical Perspective

• While diarrhea is a potential side effect of famotidine, it is generally well-tolerated compared to many other medications used for acid suppression 2, 3
• The benefit-risk profile of famotidine remains favorable for most patients requiring H2 receptor antagonist therapy 1, 5
• When prescribing famotidine, patients should be informed about the possibility of diarrhea as a side effect, though they can be reassured that it is relatively uncommon 1, 3