Famotidine Dosing for Adults
For most adult indications, famotidine 20 mg twice daily or 40 mg once daily at bedtime are the standard doses, with the FDA-approved regimens varying by specific condition. 1
Standard Dosing by Indication
Active Duodenal Ulcer
- 40 mg once daily at bedtime OR 20 mg twice daily for up to 8 weeks 1
- Both regimens demonstrate equivalent effectiveness in clinical trials 1, 2
- Most patients heal within 4 weeks; consider an additional 2-4 weeks if not healed 1
Active Gastric Ulcer
- 40 mg once daily for up to 8 weeks 1
- This higher once-daily dose is preferred over divided dosing for gastric ulcers 1
Gastroesophageal Reflux Disease (GERD)
Non-erosive GERD:
- 20 mg twice daily for up to 6 weeks 1
Erosive Esophagitis:
- 20 mg twice daily OR 40 mg twice daily for up to 12 weeks 1
- The twice-daily 20 mg regimen provides superior daytime heartburn relief and antacid consumption reduction compared to single bedtime dosing 3
Duodenal Ulcer Recurrence Prevention
- 20 mg once daily at bedtime for up to 1 year 1
Pathological Hypersecretory Conditions (e.g., Zollinger-Ellison)
- Starting dose: 20 mg every 6 hours, titrated to individual needs 1
- Maximum dose: 160 mg every 6 hours 1
- Mean effective dose in clinical practice is approximately 330 mg/day 2
Dosing Adjustments for Renal Impairment
Moderate Renal Impairment (CrCl 30-60 mL/min):
- Reduce to 20 mg once daily OR 40 mg every other day for most indications 1
Severe Renal Impairment (CrCl <30 mL/min):
- Reduce to 20 mg every other day for most indications 1
- Avoid use in pathological hypersecretory conditions with severe renal impairment 1
Alternative Routes of Administration
Intramuscular Administration
- 20 mg IM provides acid suppression for approximately 6 hours 4
- Used perioperatively when oral/IV routes unavailable 4
- The American Society of Anesthesiologists recognizes this as effective for reducing gastric volume and acidity 4
Intravenous Administration (Anaphylaxis Context)
- While not famotidine-specific, H2-blockers in anaphylaxis are dosed differently: ranitidine 50 mg IV in adults is the referenced H2-blocker dose 5
- H2-blockers are second-line therapy only and never used alone in anaphylaxis 5
Pharmacodynamic Considerations
Duration of Action
- Oral famotidine provides antisecretory activity for 10-12 hours 6
- This supports twice-daily dosing for conditions requiring sustained acid suppression 7
- Onset of action occurs within 1 hour, with maximum effect at 1-3 hours 6
Potency Comparison
- Famotidine is 20-50 times more potent than cimetidine and 7.5-8 times more potent than ranitidine on a weight basis 2, 8
Important Clinical Caveats
Tachyphylaxis
- Develops within 6 weeks of continuous H2-receptor antagonist therapy 4, 9
- Requires periodic reassessment of continued need for therapy 4
Drug Interaction Advantage
- Famotidine does not interfere with clopidogrel's antiplatelet activity, making it preferred over PPIs in patients on dual antiplatelet therapy 7, 4
- Does not alter hepatic drug metabolism unlike cimetidine 2, 8