H2-receptor antagonist indicated for active duodenal ulcer, active gastric ulcer, symptomatic nonerosive GERD and erosive esophagitis due to GERD, and reduction of duodenal ulcer recurrence risk.
Also known as: Pepcid, famotidine
DailyMed approved label (Ibuprofen and Famotidine Tablet, Doctor Reddy; setID 9f5de6af-e555-4efd-a3ed-b72c34c051b6).
DailyMed approved label (Ibuprofen and Famotidine Tablet, Doctor Reddy; setID 9f5de6af-e555-4efd-a3ed-b72c34c051b6).
Famotidine + itraconazole: famotidine reduces itraconazole absorption (gastric pH-dependent) — separate doses.
The FDA famotidine label documents the class of gastric pH-dependent drugs ("Drugs Dependent on Gastric pH for Absorption... may be significantly reduced leading to loss of efficacy", 7.1). Itraconazole capsules require an acidic pH for adequate absorption; famotidine acid suppression reduces its bioavailability and may compromise treatment of fungal infections (e.g., onychomycosis, aspergillosis). The practical guidance is to separate doses by at least 2 hours; when acid suppression is continuous, consider itraconazole oral solution (less pH-dependent) or an alternative antifungal. Assess clinical response to the antifungal during the combination.
Famotidine + itraconazole: famotidine reduces itraconazole absorption (pH-dependent) — separate doses by ≥ 2 hours.
The FDA famotidine label documents the class: "Drugs Dependent on Gastric pH for Absorption: Systemic exposure of the concomitant drug may be significantly reduced leading to loss of efficacy" (7.1). Itraconazole (capsules) requires an acidic pH — famotidine acid suppression reduces its absorption.
Assess response to antifungal therapy during the combination.
Failure of antifungal treatment with simultaneous famotidine intake.
Separate doses by at least 2 hours; consider itraconazole oral solution (less pH-dependent) if needed.
DailyMed/FDA (NIH/NLM) — approved Famotidine label (TEVA), section 7.1: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4c6f4f9e-f3f5-4ecf-9f40-887e037e8847 ; approved Itraconazole label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=a4d555fa-787c-40fb-bb7d-b0d4f7318fd0
Famotidine + tizanidine: famotidine may substantially increase tizanidine concentrations (CYP1A2) — avoid if possible.
The FDA tizanidine label documents that moderate or weak CYP1A2 inhibitors should be avoided concomitantly (section 7.2), as they may cause hypotension, bradycardia or excessive drowsiness; famotidine is a known CYP1A2 inhibitor. Tizanidine is metabolised predominantly by this enzyme (oral bioavailability of ~40% due to first-pass effect): CYP1A2 inhibition raises plasma concentrations of the muscle relaxant and potentiates its central and cardiovascular adverse effects. The combination is common in patients with spasticity and dyspepsia/GERD, so clinical vigilance is important in the first weeks. If adverse reactions occur, reduce the tizanidine dose or stop one of the drugs; avoid the combination whenever there is an alternative.
Tizanidine + famotidine: CYP1A2 inhibition by famotidine may increase tizanidine exposure — monitor for hypotension, bradycardia and drowsiness.
The FDA famotidine label documents: "Tizanidine (CYP1A2) Substrate: Potential for substantial increases in blood concentrations of tizanidine resulting in hypotension, bradycardia or excessive drowsiness; avoid concomitant use, if possible" (7.2). Famotidine inhibits CYP1A2, reducing tizanidine metabolism.
Monitor blood pressure, heart rate and level of sedation at the start of the combination.
Orthostatic hypotension, bradycardia or excessive sedation with the combination.
Avoid the combination; if unavoidable, reduce the tizanidine dose and monitor for hypotension, bradycardia and sedation.
DailyMed/FDA (NIH/NLM) — approved Tizanidine label (section 7.2): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=8d0b2b22-e1df-4ad5-92e6-f9a369108e4b ; approved Famotidine label (TEVA): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4c6f4f9e-f3f5-4ecf-9f40-887e037e8847
Famotidine + ketoconazole: famotidine reduces ketoconazole absorption (gastric pH-dependent) — separate doses.
The FDA famotidine label documents the class of gastric pH-dependent drugs: "Drugs Dependent on Gastric pH for Absorption: Systemic exposure of the concomitant drug may be significantly reduced leading to loss of efficacy" (section 7.1). Ketoconazole (tablets) requires an acidic gastric pH to dissolve and absorb — famotidine acid suppression markedly reduces its bioavailability and may lead to failure of antifungal treatment (e.g., oesophageal or systemic candidiasis). The practical guidance is to separate doses by at least 2 hours, prefer giving ketoconazole with an acidic drink and, if acid suppression is continuous, consider a less pH-dependent antifungal alternative (e.g., fluconazole). Assess clinical response to the antifungal during the combination.
Famotidine + ketoconazole: famotidine reduces ketoconazole absorption (pH-dependent) — separate doses by ≥ 2 hours.
The FDA famotidine label documents: "Drugs Dependent on Gastric pH for Absorption: Systemic exposure of the concomitant drug may be significantly reduced leading to loss of efficacy" (7.1). Ketoconazole requires an acidic gastric pH for absorption — famotidine-induced acid suppression markedly reduces its bioavailability.
Assess response to antifungal therapy during the combination.
Failure of antifungal treatment with simultaneous famotidine intake.
Separate doses by at least 2 hours; prefer giving ketoconazole with an acidic drink; consider an alternative antifungal if there is failure.
DailyMed/FDA (NIH/NLM) — approved Famotidine label (TEVA), section 7.1: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4c6f4f9e-f3f5-4ecf-9f40-887e037e8847 ; approved Ketoconazole label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=dd0da52b-fc82-4ec9-854c-0d7c52e926fb
Famotidine + atazanavir: famotidine reduces atazanavir absorption (gastric pH-dependent) — risk of virological failure.
The FDA famotidine label documents the class of gastric pH-dependent drugs (7.1). Atazanavir is an HIV protease inhibitor whose absorption depends on an acidic pH; famotidine acid suppression significantly reduces its plasma exposure, with a risk of virological failure and viral resistance. This is one of the most relevant interactions in HIV patients requiring acid suppression. The practical guidance is to follow atazanavir-specific recommendations: give famotidine 10-12 hours before or after the atazanavir dose (recommended spacing) and consider increasing the atazanavir dose (with ritonavir) when indicated; monitor viral load during prolonged combination. Alternatively, prefer an H2 antagonist or PPI with less documented impact, under specialist guidance.
Famotidine + atazanavir: famotidine reduces atazanavir absorption (pH-dependent) — risk of virological failure.
The FDA famotidine label documents the class of gastric pH-dependent drugs (7.1). Atazanavir is a protease inhibitor that requires an acidic pH for absorption — famotidine acid suppression markedly reduces its exposure, with a risk of virological failure in HIV.
Monitor HIV viral load during prolonged combination.
Virological failure or rising viral load in an HIV patient taking famotidine and atazanavir.
Separate doses by at least 10-12 hours when possible; consult atazanavir-specific recommendations (spacing and dose); consider an alternative.
DailyMed/FDA (NIH/NLM) — approved Famotidine label (TEVA), section 7.1: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4c6f4f9e-f3f5-4ecf-9f40-887e037e8847 ; approved Atazanavir label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=165cff62-b284-4a27-a65d-9ec8a5bfcdd8
Food does not clinically affect famotidine absorption.
May be taken with or without food, as preferred.
EMC-UK (MHRA) — approved Famotidine SmPC: https://www.medicines.org.uk/emc/product/100584/smpc
Famotidine is predominantly renally eliminated; its half-life is prolonged in severe renal impairment.
Reduce the dose in severe renal impairment.
EMC-UK (MHRA) — approved Famotidine SmPC: https://www.medicines.org.uk/emc/product/100584/smpc
Data on famotidine in pregnancy are limited; H2 antagonists are used when antacids are insufficient.
Use only if the benefit outweighs the risk, preferably in the 2nd/3rd trimester.
Excreted into breast milk in small amounts; compatible with breastfeeding.
No specific additional contraception.
EMC-UK (MHRA) — approved Famotidine SmPC: https://www.medicines.org.uk/emc/product/100584/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
H2 antagonist that inhibits basal and nocturnal gastric acid secretion, as well as food- and pentagastrin-stimulated secretion. Inhibition of 86% (20 mg) and 94% (40 mg) of nocturnal acid secretion, for at least 10 hours.
Competitive inhibition of histamine H2 receptors on parietal cells, suppressing acid concentration and volume of gastric secretion; pepsin secretion varies proportionally to volume.
Incomplete absorption (oral bioavailability 40–45%); plasma peaks at 1–3 hours; plasma protein binding 15–20%. Bioavailability may slightly increase with food and decrease with antacids.
Minimal first-pass metabolism; 25–30% of an oral dose is recovered unchanged in urine. The only metabolite identified in humans is the S-oxide.
Elimination half-life of 2.5–3.5 h; eliminated by renal (65–70%) and metabolic (30–35%) routes.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
