Famotidine
Indications
| Indication | Approved Population | Therapy Type | Status |
|---|---|---|---|
| Active duodenal ulcer | Adults and paediatric patients ≥40 kg | Monotherapy | FDA Approved |
| Active gastric ulcer | Adults and paediatric patients ≥40 kg | Monotherapy | FDA Approved |
| Symptomatic nonerosive GERD | Adults and paediatric patients ≥40 kg | Monotherapy | FDA Approved |
| Erosive esophagitis due to GERD (diagnosed by biopsy) | Adults and paediatric patients ≥40 kg | Monotherapy | FDA Approved |
| Pathological hypersecretory conditions (e.g., Zollinger-Ellison syndrome, multiple endocrine neoplasias) | Adults only | Monotherapy | FDA Approved |
| Reduction of the risk of duodenal ulcer recurrence | Adults only | Monotherapy | FDA Approved |
Famotidine is a competitive inhibitor of histamine H2-receptors on parietal cells. It reduces both basal and stimulated gastric acid secretion by blocking histamine binding. The 20 mg and 40 mg tablet formulations are not recommended in paediatric patients weighing less than 40 kg because the lowest available tablet strength exceeds the recommended dose for these patients; another famotidine formulation (e.g., oral suspension) should be used instead.
Stress ulcer prophylaxis — Evidence quality: Moderate. Famotidine is used in critically ill patients for stress-related mucosal injury prevention, although PPIs have become more commonly used in this setting.
Refractory chronic urticaria — Evidence quality: Moderate. H2-receptor antagonists including famotidine are used as adjunctive therapy with H1-antihistamines for chronic urticaria that does not respond to H1-blockers alone.
Dosing
Adult and Paediatric (≥40 kg) Dosing — Normal Renal Function
| Indication | Recommended Dose | Duration | Notes |
|---|---|---|---|
| Active duodenal ulcer | 40 mg once daily or 20 mg twice daily | Up to 8 weeks | Most patients heal within 4 weeks; if not healed, continue 2–4 additional weeks |
| Active gastric ulcer | 40 mg once daily | Up to 8 weeks | — |
| Symptomatic nonerosive GERD | 20 mg twice daily | Up to 6 weeks | — |
| Erosive esophagitis due to GERD | 20 mg twice daily or 40 mg twice daily | Up to 12 weeks | Both regimens effective per clinical trials |
| Pathological hypersecretory conditions (adults only) | 20 mg every 6 hours | As clinically indicated | Adjust to individual patient needs; maximum 160 mg every 6 hours |
| DU recurrence risk reduction (adults only) | 20 mg once daily | 1 year | Longer durations not studied |
Renal Impairment Dosing
| Indication | CrCl 30–60 mL/min | CrCl <30 mL/min |
|---|---|---|
| Active DU | 20 mg QD or 40 mg QOD | 20 mg QOD Alt: 10 mg QD (use alternate formulation) |
| Active GU | 20 mg QD or 40 mg QOD | 20 mg QOD Alt: 10 mg QD (use alternate formulation) |
| Symptomatic nonerosive GERD | 20 mg QD | 20 mg QOD Alt: 10 mg QD (use alternate formulation) |
| Erosive esophagitis (from 20 mg BID regimen) | 20 mg QD | 20 mg QOD Alt: 10 mg QD (use alternate formulation) |
| Erosive esophagitis (from 40 mg BID regimen) | 40 mg QD | 20 mg QD |
| Pathological hypersecretory conditions | Avoid use | Avoid use |
| DU recurrence risk reduction | 20 mg QOD | 10 mg QOD Use alternate formulation for 10 mg dose |
Take once daily before bedtime or twice daily in the morning and before bedtime. May be taken with or without food, and may be given concurrently with antacids. The antisecretory effect lasts approximately 10–12 hours. No hepatic dose adjustment is required — liver cirrhosis does not significantly affect famotidine disposition unless severe renal insufficiency coexists.
Pharmacology
Mechanism of Action
Famotidine is a competitive inhibitor of histamine H2-receptors on gastric parietal cells. By blocking the action of histamine at these receptors, famotidine inhibits both basal and stimulated gastric acid secretion, reducing both the acid concentration and volume of gastric secretion. Changes in pepsin secretion are proportional to volume output. Unlike proton pump inhibitors, which irreversibly block the H+/K+-ATPase proton pump, famotidine acts upstream by blocking one of the three stimulatory pathways (histamine, acetylcholine, and gastrin) that converge on the parietal cell. This results in a less complete but faster-onset acid suppression compared to PPIs, with clinical effects evident within 1 hour of oral administration.
ADME Profile
| Parameter | Value | Clinical Implication |
|---|---|---|
| Absorption | Oral bioavailability 40–50% (incomplete absorption); Tmax 2–4 h; onset of antisecretory action within 1 h; dose-independent absorption (5–40 mg range); food does not significantly affect bioavailability; potent antacids may reduce absorption by 20–30% | Can be taken with or without food; faster onset than PPIs; can co-administer with antacids per PI (despite modest absorption reduction) |
| Distribution | Protein binding 15–22% (low); Vd 1.0–1.3 L/kg | Low protein binding means famotidine is readily removed by haemodialysis; moderate tissue distribution |
| Metabolism | Minimal first-pass hepatic metabolism; weak CYP1A2 inhibitor; minimal interference with hepatic cytochrome P450 system; no clinically significant effects on CYP2D6, CYP3A4, or other CYP isoforms | Very low drug interaction potential compared to cimetidine; no hepatic dose adjustment required; liver cirrhosis does not alter disposition unless severe renal impairment coexists |
| Elimination | t½ 2.5–3.5 h; 65–70% excreted unchanged in urine; renal clearance ~15 L/h (exceeds GFR, indicating tubular secretion); eliminated by haemodialysis; t½ can exceed 20 h in severe renal impairment (CrCl <10 mL/min); antisecretory effect duration ~10–12 h | Predominantly renal elimination necessitates dose reduction in moderate-severe renal impairment; CNS adverse reactions and QT prolongation risk increase with renal impairment due to drug accumulation |
Side Effects
In clinical trials of approximately 2,500 patients (1,442 treated with famotidine), the overall adverse reaction incidence in the famotidine 40 mg at bedtime group was similar to placebo. The population ranged from 17 to 91 years of age.
| Adverse Effect | Frequency | Clinical Note |
|---|---|---|
| Headache | ≥1% | Most commonly reported; incidence similar to placebo |
| Dizziness | ≥1% | Incidence similar to placebo |
| Constipation | ≥1% | Incidence similar to placebo |
| Diarrhoea | ≥1% | Listed in highlights; incidence similar to placebo |
| System | Adverse Effects |
|---|---|
| Body as a Whole | Fever, asthenia, fatigue |
| Cardiovascular | Palpitations |
| Gastrointestinal | Elevated liver enzymes, vomiting, nausea, abdominal discomfort, anorexia, dry mouth |
| Haematologic | Thrombocytopenia |
| Hypersensitivity | Orbital oedema, rash, conjunctival injection, bronchospasm |
| Musculoskeletal | Musculoskeletal pain, arthralgia |
| Nervous System / Psychiatric | Seizure, hallucinations, depression, anxiety, decreased libido, insomnia, somnolence |
| Skin | Pruritus, dry skin, flushing |
| Special Senses | Tinnitus, taste disorder |
| Other | Impotence |
| Adverse Effect | System | Required Action |
|---|---|---|
| Arrhythmia, AV block, prolonged QT interval | Cardiovascular | ECG monitoring; higher risk in renal impairment if dose/interval not adjusted |
| Cholestatic jaundice, hepatitis | Gastrointestinal | Monitor LFTs; discontinue if hepatotoxicity suspected |
| Agranulocytosis, pancytopenia, leukopenia | Haematologic | CBC monitoring; discontinue if blood dyscrasia occurs |
| Anaphylaxis, angioedema, facial oedema, urticaria | Hypersensitivity | Immediate discontinuation; emergency care |
| Rhabdomyolysis, muscle cramps | Musculoskeletal | Check CK; discontinue if rhabdomyolysis confirmed |
| Confusion, agitation, paresthesia | Nervous System | Reduce dose or discontinue; higher risk in elderly and renal impairment |
| Interstitial pneumonia | Respiratory | Discontinue; pulmonary workup |
| Toxic epidermal necrolysis / Stevens-Johnson syndrome | Skin | Immediate discontinuation; emergency care |
Confusion, delirium, hallucinations, disorientation, agitation, seizures, and lethargy have been reported in elderly patients and patients with moderate and severe renal impairment. Famotidine blood levels are higher in these patients. Use the lowest effective dose and monitor renal function.
Drug Interactions
Famotidine has a much lower drug interaction potential than cimetidine. Unlike cimetidine, famotidine does not significantly inhibit hepatic cytochrome P450 enzymes (except for weak CYP1A2 inhibition). The primary interaction mechanism is pH-dependent absorption changes for co-administered drugs.
Unlike cimetidine, which is a potent inhibitor of multiple CYP enzymes (1A2, 2C9, 2D6, 3A4), famotidine has a much cleaner interaction profile. Its only CYP effect is weak CYP1A2 inhibition, which is clinically relevant primarily for tizanidine. This makes famotidine the preferred H2-receptor antagonist when drug interactions are a concern.
Monitoring
- Renal FunctionBaseline and periodically
RoutineAssess CrCl at baseline to determine dosing. Monitor periodically in elderly and in patients with known or suspected renal impairment. Half-life can exceed 20 hours when CrCl <10 mL/min. - CNS StatusOngoing in at-risk patients
Trigger-basedMonitor elderly patients and those with renal impairment for confusion, delirium, hallucinations, disorientation, agitation, seizures, or lethargy. Consider dose reduction if CNS effects develop. - Symptom Response4–8 weeks
RoutineAssess healing at end of treatment course. Symptomatic response does not preclude gastric malignancy — consider endoscopy or further evaluation if suboptimal response or early relapse, especially in adults. - CBCIf symptoms develop
Trigger-basedPost-marketing reports of agranulocytosis, pancytopenia, and leukopenia. Monitor if unexplained fever, infection, or bleeding occur. - QT IntervalIf renal impairment present
Trigger-basedProlonged QT interval reported in patients with renal impairment whose dose or dosing interval was not adjusted appropriately. ECG monitoring may be warranted.
Contraindications & Cautions
Absolute Contraindications
- History of serious hypersensitivity reactions (e.g., anaphylaxis) to famotidine or other H2-receptor antagonists
Use with Caution
- Moderate-severe renal impairment (CrCl <60 mL/min) — dose reduction required; increased risk of CNS adverse reactions and QT prolongation due to drug accumulation
- Elderly patients — use lowest effective dose; monitor renal function; higher risk of CNS adverse reactions
- Pathological hypersecretory conditions with renal impairment — avoid use in patients with CrCl <60 mL/min; doses required may exceed those evaluated in renally impaired patients
- Pregnancy — insufficient human data; use only if clearly needed. Animal studies showed no adverse effects at up to 243× the MRHD in rats and 122× in rabbits
- Lactation — limited data on presence in human milk; no effects on breastfed infant reported; weigh benefits of breastfeeding against clinical need
- Paediatric patients <40 kg — use alternate formulation (e.g., oral suspension); 20 mg and 40 mg tablets exceed recommended doses in these patients
Confusion, delirium, hallucinations, disorientation, agitation, seizures, and lethargy have been reported in elderly patients and patients with moderate and severe renal impairment treated with famotidine. Since famotidine blood levels are higher in patients with renal impairment, dosage adjustments are recommended.
Patient Counselling
Purpose of Therapy
Famotidine is an acid-reducing medication that blocks histamine receptors in the stomach. It is used to treat and prevent ulcers in the stomach and duodenum, relieve heartburn and GERD symptoms, and help heal damage to the oesophagus caused by acid reflux.
How to Take
Take famotidine once daily at bedtime or twice daily in the morning and at bedtime. It can be taken with or without food and may be given alongside antacids. Shake the liquid suspension vigorously for 5–10 seconds before each dose. Most ulcers heal within 4 weeks but may take up to 8 weeks. Complete the full prescribed course even if symptoms improve.
Sources
- Famotidine tablets prescribing information. Aurobindo Pharma Limited. Revised 4/2022. dailymed.nlm.nih.govCurrent FDA-approved PI — primary source for indications, dosing Tables 1 and 2, adverse reactions, drug interactions, and renal impairment recommendations.
- PEPCID (famotidine) tablets prescribing information. Merck Sharp & Dohme. 2018. accessdata.fda.govBrand-name PEPCID PI including clinical trial data, paediatric dosing guidance, and pharmacodynamics.
- Famotidine injection prescribing information. Sagent Pharmaceuticals. Revised 2025. accessdata.fda.govInjectable formulation PI with IV-specific dosing, benzyl alcohol neonatal warning, and CNS adverse reaction warnings.
- Gitlin N, McCullough AJ, Smith JL, et al. A multicenter, double-blind, randomized, placebo-controlled comparison of nocturnal and twice-a-day famotidine in the treatment of active duodenal ulcer disease. Gastroenterology. 1987;92(1):48–53.Pivotal DU healing trial: 70% healed at week 4, 83% at week 8 with famotidine 40 mg QHS vs 45% placebo.
- McCullough AJ, Graham DY, Knuff TE, et al. Suppression of nocturnal acid secretion with famotidine accelerates gastric ulcer healing. Gastroenterology. 1989;97(4):860–866.GU healing trial demonstrating famotidine 40 mg QHS efficacy for gastric ulcer.
- Katz PO, Dunbar KB, Schnoll-Sussman FH, et al. ACG Clinical Guideline for the Diagnosis and Management of Gastroesophageal Reflux Disease. Am J Gastroenterol. 2022;117(1):27–56. doi:10.14309/ajg.0000000000001538Current GERD guideline positioning H2RAs as step-down therapy or for nocturnal acid breakthrough when combined with PPIs.
- Lanza FL, Chan FK, Quigley EM, et al. Guidelines for prevention of NSAID-related ulcer complications. Am J Gastroenterol. 2009;104(3):728–738. doi:10.1038/ajg.2009.115ACG guideline noting famotidine reduces NSAID-related duodenal but not gastric ulcers; PPIs preferred for gastroprotection.
- Feldman M, Burton ME. Histamine2-receptor antagonists: standard therapy for acid-peptic diseases (first of two parts). N Engl J Med. 1990;323(24):1672–1680. doi:10.1056/NEJM199012133232405Comprehensive NEJM review of H2RA pharmacology including famotidine’s relative potency vs cimetidine and ranitidine.
- Langtry HD, Grant SM, Goa KL. Famotidine: an updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic use in peptic ulcer disease and other allied diseases. Drugs. 1989;38(4):551–590. doi:10.2165/00003495-198938040-00004Major therapeutic review of famotidine covering clinical pharmacology, efficacy, and tolerability.
- Echizen H, Ishizaki T. Clinical pharmacokinetics of famotidine. Clin Pharmacokinet. 1991;21(3):178–194. doi:10.2165/00003088-199121030-00003Key PK review: t½ 2–4 h, bioavailability 40–50%, protein binding 15–22%, Vd 1.0–1.3 L/kg, renal clearance 15 L/h, 70% eliminated unchanged; reduced clearance in renal impairment and elderly.
- Lin JH, Chremos AN, Yeh KC, et al. Effects of age, gender, and race on the pharmacokinetics of famotidine. Br J Clin Pharmacol. 1989;27(S1):55S–59S.Population PK study showing famotidine clearance correlates with CrCl; age-related pharmacokinetic changes driven by renal function decline.
- Famotidine. In: StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing; Updated September 2025. ncbi.nlm.nih.govComprehensive evidence-based review of famotidine pharmacology, indications, dosing, and monitoring recommendations.