famotidine
Brand: Pepcid
Prototype Drug
Drug Class: H2 receptor antagonist
Drug Family: GI agent
Subclass: histamine H2 receptor antagonist
Organ Systems: gastrointestinal
Mechanism of Action
Competitive antagonist at histamine H2 receptors on gastric parietal cells; reversibly reduces acid secretion; less profound than PPIs but faster onset.
histamine H2 receptor on parietal cells
Indications
- GERD
- PUD
- Zollinger-Ellison (high doses)
- heartburn OTC
- NSAID gastroprotection
Contraindications
- hypersensitivity
Adverse Effects
Common
- headache
- dizziness
- constipation
- diarrhea
Serious
- confusion in elderly (less than cimetidine)
- rare thrombocytopenia
Pharmacokinetics (ADME)
| Absorption | ~40-45% oral |
| Distribution | moderate |
| Metabolism | minimal hepatic (30% hepatic) |
| Excretion | renal unchanged 25-30% |
| Half-life | 2.5-4 hours |
| Onset | 1-3 hours |
| Peak | 1-3 hours |
| Duration | 6-12 hours |
| Protein Binding | 15-20% |
| Vd | 1.1-1.4 L/kg |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| antacids | reduce famotidine absorption (separate by 2 hours) | minor |
Nursing Considerations
- Preferred H2RA over cimetidine (fewer drug interactions)
- Available OTC for heartburn
- H2RA inferior to PPI for severe GERD but useful for breakthrough symptoms
- Renal dose adjustment required for CrCl <50
Clinical Pearls
- Fewest drug interactions of all H2RAs (cimetidine inhibits CYP450, famotidine does not)
- COVID-19 anecdotal use: famotidine was investigated but evidence not established
Safety Profile
Pregnancy safe
Lactation use-with-caution
Renal Adjustment Required
Hepatic Adjustment Not required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.