Famotidine Drug Interactions

by on May 1, 2012

Famotidine (Pepcid) can potentially cause side effects and interactions when used in combination with other drugs. Before taking this medication, patients should discuss any other drugs they are taking with their doctor or pharmacist.

It is also suggested that medicines that contain aspirin or NSAIDs, such as ibuprofen, celebrex or naproxen (aleve), not be taken in at the same time as famotidine. This is because the combination of these medications can potentially cause stomach ulcers or irritation.

Unlike some of the firstly developed H2 blockers (such as cimetidine), famotidine has shown no significant effect on the cytochrome P450 enzyme system. This is a constellation of enzymes that metabolizes a lot of drugs. Cimetidine, for example, inhibits the activity of these enzymes and thus contributes to a decrease in the metabolism of many drugs. Warfarin, phenytoin and diazepam (metabolized by cytochrome P450 enzymes) have been tested and no interactions with famotidine have been identified. This makes famotidine one of the safest H2 blockers.

However, famotidine may interfere with the absorption of some antifungal medicines:

  • Ketoconazole (Nizoral) and Itraconazole (Orungal) are better absorbed in low pH (acidic) environment. In other words inhibiting the production of stomach acid by famotidine can lead to a weaker effect of these antifungal medicines. In order to avoid this effect, famotidine should be taken at least two hours after these drugs.

It is recommended to take famotidine during meals because food increases its absorption. Avoid drinking alcohol if you are treated with famotidine as alcohol has an irritating effect on the stomach mucosa and may increase the time needed for the ulcer healing. Taking NSIDs (Nonsteroidal anti-inflammatory drugs) can also have an irritating effect on the stomach lining.

Although famotidine is often combined with antiacids in a number of formulations, antiacids can decrease its effect. So if you have been prescribed a long-term treatment with famotidine, consult your physician about the use of antiacids. In general, in case you need to take antiacids, it is recommended to take them two hours after famotidine.

Famotidine may interfere with the absorption of:

  • Dasatinib (Sprycel) – this is a medicine used for the treatment of chronic myelogenous leukemia. Sprycel is best absorbed in the presence of stomach acid.
  • Some anti-HIV drugs, such as Reyataz (Atazanavir), Rescriptor (delavirdine), Lexiva (fosamprenavir calcium), Agenerase(amprenavir)–these medicines require acidic environment for best absorption. If you still need to take famotidine, a 12 –hour interval between the medicines is recommended. Sometimes a dose adjustment of famotidine may be necessary. Consult your physician about the best way of combining these medicines.

This list is not complete and other drugs can also interfere with famotidine. Please inform your doctor about any other medicines that you are using, including over-the-counter ones, herbs and dietary supplements.