Chemical formula: C₈H₁₅N₇O₂S₃ Molecular mass: 337.445 g/mol PubChem compound: 3325
Famotidine interacts in the following cases:
Since famotidine is excreted primarily by the kidney, caution should be observed in patients with impaired renal function. Patients with renal impairment should consult a physician before using famotidine. A reduction in daily dosage should be considered if creatinine clearance falls below 10 mL/min.
Antacids may decrease the absorption of famotidine and lead to lower plasma concentrations of famotidine. Famotidine should therefore be taken 1-2 hours before the administration of an antacid.
Alterations of gastric pH may affect the bioavailability of certain drugs resulting in a decrease in the absorption of atazanavir.
Risk of loss of efficacy of calcium carbonate when co-administered as phosphate binder with famotidine in haemodialysis patients.
The absorption of ketoconazole and itraconazole could be reduced. Ketoconazole should be given 2 hours before famotidine administration. Patients should consult a physician before using this product together with itraconazole. Concomitant use of famotidine with the antifungal agent itraconazole results in significantly reduced peak and trough plasma concentrations of itraconazole, which may result in reduced antifungal efficacy.
The administration of probenecid can delay the elimination of famotidine. Concomitant use of probenecid and famotidine should be avoided.
Due to its H2-antagonist effect, famotidine may also decrease the absorption of rilpivirine.
The concomitant use of sucralfate should be avoided within two hours of the famotidine dose.
Famotidine may decrease the absorption of ulipristal.
Due to its H2-antagonist effect, famotidine may also decrease the absorption of cyanocobalamine.
There are no adequate and well-controlled studies in pregnant women. Famotidine should not be used during pregnancy unless the potential benefit of treatment to the mother outweighs the possible risks to the developing foetus.
Reproductive studies have been performed in rats and rabbits at oral doses of up to 2000 and 500 mg/kg/day, respectively, and in both species at I.V. doses of up to 200 mg/kg/day, and have revealed no significant evidence of impaired fertility or harm to the fetus due to famotidine. While no direct fetotoxic effects have been observed, sporadic abortions occurring only in mothers displaying marked decreased food intake were seen in some rabbits at oral doses of 200 mg/kg/day (250 times the usual human dose) or higher. There are, however, no adequate or well-controlled studies in pregnant women. Because animal reproductive studies are not always predictive of human response, this drug should be used during pregnancy only if clearly needed.
Famotidine is distributed in breast milk. A risk to newborns/infants cannot be excluded. A decision must be made whether to discontinue breast-feeding or to discontinue/abstain from therapy with famotidine taking into account the benefit of breast-feeding for the infant and the benefit of therapy for the mother.
Studies performed in lactating rats have shown that famotidine is secreted into breast milk. Transient growth depression was observed in young rats suckling from mothers treated with maternotoxic doses of at least 600 times the usual human dose. Famotidine is detectable in human milk. Because of the potential for serious adverse reactions in nursing infants from famotidine, a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.
Some patients have experienced adverse reactions such as dizziness and headache while taking famotidine. Patients should be informed that they should avoid driving vehicles or operating machinery or doing activities which require prompt vigilance if they experience these symptoms.
Adverse drug reactions (ADRs) identified during clinical trials and post-marketing experience with famotidine are listed below by System Organ Class (SOC). The frequencies are defined in accordance with current guidance, as: Very Common (≥1/10), Common (≥1/100, <1/10), Uncommon (≥1/1,000, <1/100), Rare (≥1/10,000, <1/1,000), Very rare (<1/10,000), Not known (cannot be estimated from the available data).
ADRs are presented by frequency category based on incidence in adequately designed clinical trials or epidemiology studies.
Very rare: Agranulocytosis, Leucopenia**, Neutropenia, Pancytopenia**, Thrombocytopenia
Very rare: Hypersensitivity (Anaphylactic reaction, Angioedema, Bronchospasm)
Uncommon: Decreased appetite
Very rare: Agitation, Anxiety disorder, Confusional state, Depression, Disorientation, Hallucination, Insomnia, Libido decreased, Mental disorder
Common*: Headache, Dizziness
Uncommon: Dysgeusia
Rare*: Somnolence
Very rare: Generalised tonic-clonic seizure (particularly in patients with impaired renal function), Paraesthesia, Seizure
Very rare: Atrioventricular block (with H2-receptor antagonists administered intravenously)
Very rare: Interstitial lung disease (sometimes fatal)
Common: Constipation, Diarrhoea
Uncommon: Abdominal discomfort and pain, Abdominal distension, Dry mouth, Flatulence, Nausea and/or Vomiting
Rare: Liver disorder**
Very rare: Cholestatic jaundice, Hepatitis
Uncommon: Rash, Pruritus, Urticaria
Very rare: Alopecia, Stevens-Johnson syndrome/Toxic epidermal necrolysis (sometimes fatal)
Very rare: Arthralgia, Muscle spasms
Rare: Gynaecomastia***
Very rare: Erectile dysfunction
Uncommon: Asthenia, Fatigue
Very rare: Chest discomfort
Rare: Malaise
Very rare: Hepatic enzyme abnormal
* not significantly greater than placebo (p<0.05)
** A causal relationship to therapy with famotidine has not been established
*** Reversible on discontinuing treatment
No clinically significant increase in endocrine or gonadal function has been reported.
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