Drug reference

Famotidine

h2 Receptor Antagonist · Agent for gastric acid disorders

h2 Receptor AntagonistAgent for gastric acid disorders

CDSCO approvedOTC (for doses up to 20 mg/day for specific indications; otherwise likely Schedule H for higher doses)

EXCRETION

—

not curated

INTERACTIONS

12 major

SEVERE in our sources

PREGNANCY

Manufacturer advises avoid unless potential benefit outweighs risk.

FDA category + note

Top interactionssee all 12 →

AtazanavirSevereDatabaseDDInter
DasatinibSevereDatabaseDDInter
ErlotinibSevereDatabaseDDInter
NeratinibSevereDatabaseDDInter

Mechanism

Famotidine competitively and reversibly blocks histamine H2 receptors on gastric parietal cells, suppressing both basal and stimulated gastric acid secretion. It is the most potent H2 receptor antagonist on a per-milligram basis — approximately 20-fold more potent than cimetidine and 7-fold more potent than ranitidine. Unlike cimetidine, famotidine does not inhibit cytochrome P450 enzymes or bind androgen receptors, providing a cleaner drug interaction and side effect profile.

Indications

Treatment of benign gastric and duodenal ulcerationMaintenance treatment of duodenal ulcerationReflux oesophagitisGastric acid reduction in obstetricsGastric acid reduction during surgical proceduresShort-bowel syndromeTo reduce degradation of pancreatic enzyme supplementsShort-term symptomatic relief of heartburn, dyspepsia, and hyperacidityPrevention of heartburn, dyspepsia, and hyperacidity associated with food or drink consumptionPrevention of heartburn, dyspepsia, and hyperacidity causing sleep disturbanceGastric ulcer (to promote healing)Duodenal ulcer (to promote healing)Gastroesophageal reflux disease (uncomplicated)Prevention of stress ulcersZollinger-Ellison syndromePrevention of aspiration pneumoniaDuodenal ulcerGastric ulcerStress ulcers and gastritisGastroesophageal reflux disease (GERD) (mild or stage-1 cases)Urticaria (adjuvant to H1 antagonist)

Dosing

Adult: Benign gastric and duodenal ulceration: 40 mg once daily at night for 4–8 weeks. Maintenance treatment of duodenal ulceration: 20 mg once daily at night. Reflux oesophagitis: 20–40 mg twice daily for 6–12 weeks; maintenance 20 mg twice daily. Gastric acid reduction in obstetrics: Initially 400 mg at start of labour, then up to 400 mg every 4 hours if necessary.…
Pediatric: Children over 16 years: For short-term symptomatic relief or prevention of heartburn, dyspepsia, hyperacidity, or sleep disturbance due to these symptoms, max single dose 10 mg, max daily dose 20 mg (limited to 2 weeks' supply for public sale).
Renal adjustment: Use normal dose every 36–48 hours or use half normal dose if eGFR less than 50 mL/minute/1.73 m2.
Max dose: 2.4 g per day (for gastric acid reduction in obstetrics); 20 mg per day (for OTC indications)

Pharmacokinetics

Onset

Therapeutic levels achieved rapidly after intravenous dosing.

Half-life

1 to 3 h

Bioavailability

37 (20–66)%

Protein binding

Only a small fraction is protein bound.

Metabolism

Hepatic metabolism accounts for a small fraction of clearance (<10% to ~35%).

Excretion

65–80%

Side effects

Common

Appetite decreasedDry mouthTaste alteredVomitingDiarrheaHeadacheDrowsinessFatigueMuscular painConstipationDizzinessBowel upset

Serious

Anxiety
Chest tightness
Drowsiness
Insomnia
Interstitial pneumonia
Libido decreased
Muscle cramps
Neutropenia
Paraesthesia
Psychiatric disorder
Seizures
Severe cutaneous adverse reactions (SCARs)
CNS effects (confusion, delirium, hallucinations, slurred speech, headaches), primarily with IV administration or in elderly
Various blood disorders (e.g., thrombocytopenia)
Vitamin B12 deficiency
Disorientation (rare)
Rash (rare)

Pregnancy & lactation

Pregnancy

Manufacturer advises avoid unless potential benefit outweighs risk.

Lactation

Present in milk—not known to be harmful but manufacturer advises avoid.

Drug interactions

Atazanavir

Severe

Database

Significantly reduced plasma concentrations of atazanavir, leading to loss of antiviral efficacy and potential development of drug resistance.

Coadministration is generally not recommended. If absolutely necessary, atazanavir should be given with food 2 hours before or 10 hours after famotidine. Monitor viral load closely. Consider alternative acid-suppressing agents or antiretrovirals.

Source: DDInter

Dasatinib

Severe

Database

Significantly reduced plasma concentrations of dasatinib, leading to decreased efficacy in treating chronic myeloid leukemia or acute lymphoblastic leukemia.

Coadministration is contraindicated. Avoid concomitant use. If acid suppression is required, consider antacids given at least 2 hours before or after dasatinib, or consider H2-receptor antagonists or proton pump inhibitors only if absolutely necessary and with careful monitoring.

Source: DDInter

Erlotinib

Severe

Database

Significantly reduced plasma concentrations of erlotinib, leading to decreased efficacy in treating non-small cell lung cancer or pancreatic cancer.

Coadministration is generally not recommended. If acid suppression is required, consider antacids given at least 2 hours before or after erlotinib. Avoid H2-receptor antagonists and proton pump inhibitors.

Source: DDInter

Neratinib

Severe

Database

Drug interaction classified as: absorption

Source: DDInter

Nilotinib

Severe

Database

Significantly reduced plasma concentrations of nilotinib, leading to decreased efficacy in treating chronic myeloid leukemia.

Coadministration is generally not recommended. If acid suppression is required, consider antacids given at least 2 hours before or after nilotinib. Avoid H2-receptor antagonists and proton pump inhibitors.

Source: DDInter

Ozanimod

Severe

Database

Drug interaction classified as: synergy

Source: DDInter

Pazopanib

Severe

Database

Drug interaction classified as: absorption.

Source: DDInter

Rilpivirine

Severe

Database

Significantly reduced plasma concentrations of rilpivirine, leading to loss of antiviral efficacy and potential development of drug resistance.

Coadministration is contraindicated. Avoid concomitant use. If acid suppression is required, consider alternative antiretroviral regimens or alternative acid-suppressing agents.

Source: DDInter

Selpercatinib

Severe

Database

Drug interaction classified as: absorption

Source: DDInter

Siponimod

Severe

Database

Drug interaction classified as: synergy

Source: DDInter

Tizanidine

Severe

Database

Drug interaction classified as: metabolism.

Source: DDInter

Tyrosine Kinase Inhibitors (e.g., Gefitinib, Lapatinib)

Severe

Database

Significantly reduced plasma concentrations of the tyrosine kinase inhibitor, leading to decreased efficacy in treating various cancers.

Coadministration is generally not recommended or contraindicated depending on the specific TKI. Refer to individual TKI prescribing information. If acid suppression is required, consider antacids given at least 2 hours before or after the TKI. Avoid H2-receptor antagonists and proton pump inhibitors.