As is the case with any other medication, there may be some instances where famotidine use is not recommended or usage will have to be adjusted in order to prevent or reduce the risk of negative interactions occurring with other drugs, medical conditions, or even food and drink.
According to the U.S. National Library of Medicine, drugs that may interact with famotidine include the following:
- Drugs depending on stomach pH for absorption, such as dasatinib (Sprycel), delavirdine mesylate (Rescriptor), cefditoren (Spectracef), and fosamprenavir (Lexiva) , etc.
- Tizanidine (Comfort Pac-tizanidine, Zanaflex), a CYP1A2 substrate
Please note that this list may not be complete, and other interactions with drugs not listed here may occur.
Famotidine and Stomach pH-dependent Drugs
Famotidine changes the pH of the stomach by reducing the amount of acid; it can therefore reduce the absorption of drugs that need an acidic environment to be absorbed. As a consequence, famotidine can reduce the effect of these drugs.
Some examples of pH-dependent drugs are:
- dasatinib (Sprycel),
- delavirdine mesylate (Rescriptor),
- cefditoren (Spectracef),
- fosamprenavir (Lexiva),
- atazanavir (Reyataz),
- erlotinib (Tarceva),
- ketoconazole (Xolegel, Nizoral A-D, Nizoral, Extina),
- itraconazole (Sporanox, Sporanox Pulsepak, Onmel),
- ledipasvir/sofosbuvir (Harvoni),
- nilotinib (Tasigna), and
- rilpivirine (Edurant).
Famotidine and Tizanidine (CYP1A2 Substrate)
Although not studied clinically, experts consider famotidine a weak CYP1A2 inhibitor, which means it inhibits the enzyme (specialized protein) CYP1A2. This inhibition may lead to substantial increases in blood concentrations of tizanidine, a CYP1A2 substrate (something the enzyme CYP1A2 acts on). As such, experts recommend against taking famotidine and tizanidine together.
But if concomitant (at the same time) use is necessary, monitor for hypotension (low blood pressure), bradycardia (slow heart rate), or excessive drowsiness.
Famotidine and Tums
In general, experts recommend against taking other stomach acid reducers together with famotidine. However, your doctor may suggest taking an antacid such as Tums with famotidine for an immediate relief of symptoms; only take this medication as directed by a licensed medical professional.
Famotidine and Ranitidine
Experts generally do not recommend taking famotidine with other H2 blockers, such as ranitidine (Zantac), unless your doctor expressly prescribes a combination therapy.
Food does not appear to affect absorption of famotidine or peak concentrations. However, famotidine may interact with the following nutrients:
- Folic acid
- Vitamin B12
Please note that this list may not be complete, and there may be other foods and beverages that interact with this drug.
Famotidine and Mineral Absorption
Some evidence suggests that vitamins and minerals, such as copper, iron, folic acid, and vitamin B12, require the presence of stomach acid for optimal absorption. Because famotidine reduces the acid in the stomach, it may subsequently inhibit this absorption. As a result, it may cause or otherwise contribute to a deficiency of these nutrients. To supplement such deficiencies, you may consider eating foods rich in copper, iron, folic acid, and vitamin B12 or taking supplements.
Some foods high in copper are:
- organ meats,
- shiitake mushrooms,
- nuts and seeds,
- leafy greens, and
- dark chocolate.
- tofu and soybeans,
- nuts and seeds,
- leafy vegetables,
- mushrooms and palm hearts,
- prune juice,
- mulberries, and
- whole grains like amaranth, spelt, and oats.
Food rich in folic acid include:
- leafy greens,
- citrus fruits,
- Brussels sprouts,
- nuts and seeds,
- beef liver,
- wheat germ,
- avocado, and
- fortified grains.
Food high in vitamin B12 include:
- animal liver and kidneys,
- fortified cereals,
- fortified nutritional yeast,
- fortified non-dairy milk,
- milk and other dairy products, and
Famotidine can also reduce the absorption of beta-carotene, a naturally occurring reddish-orange pigment found in plants and fungi. However, it is unknown whether taking beta-carotene supplements would solve this problem. In short, there is still little evidence on the interaction between famotidine and beta-carotene.
Magnesium and Aluminium
Lastly, taking a magnesium hydroxide or aluminium hydroxide-based antacid together with famotidine can lead to decreased famotidine absorption by 20–25%. Experts therefore recommend taking famotidine two hours before or after any aluminium or magnesium-containing antacids in order to reduce this risk.
Famotidine and Alcohol
Interactions between famotidine and alcohol have not been observed. However, drinking alcohol can worsen heartburn, ulcers, and GERD symptoms and it is, therefore, best avoided. For more information, please visit our page on famotidine and alcohol interactions.
Disease & Conditions Interactions
Sometimes certain medications can increase the risk of negative side effects for patients with certain diseases or other medical conditions.
Diseases and medical conditions that are known to negatively interact with famotidine include:
- Gastrointestinal bleeding
- Renal dysfunction
Please note that this list may not be complete, and there may be other diseases and medical conditions where patients should not take famotidine.
Famotidine and Gastrointestinal Bleeding
If you have symptoms of gastrointestinal bleeding (vomit with blood, bloody or black stools, etc.) and you are taking famotidine, consult with your doctor immediately. These symptoms might be a sign of serious conditions.
Famotidine and Renal Dysfunction
The elimination half-life of famotidine by the kidneys may be prolonged considerably in patients with severe renal (kidney) impairment, possibly exceeding 20 hours. In other words, people with severe kidney problems may process this drug much more slowly than others do. Moreover, central nervous system (CNS) adverse effects, such as grand mal seizures and psychic disturbances, have been reported in patients with renal impairment. Consequently, dosage of famotidine needs to be adjusted for these patients.
In anuric patients (patients who aren’t passing urine), the elimination half-life can be approximately 24 hours. In other words, in patients with anuresis, it can take their bodies roughly a day to clear half of this medication.
Famotidine and COVID 19
In a small observational study, non-hospitalised COVID-19 patients who gave themselves a high dose of oral famotidine showed improvement of COVID-19 symptoms within 24 hours.
Famotidine and Pregnancy
There is limited evidence on famotidine safety during pregnancy. For more information, please visit our page on famotidine and pregnancy risks.
Famotidine and Cancer
While other H2 blockers like ranitidine (Zantac) may be prone to breaking down into a cancer-causing substance, FDA testing has not found such a substance in famotidine.