Available in 10, 20, and 40 mg tablets, and injectable

Brand Names: Pepcid, Pepcid AC, Pepcid RPD

Background

Stomach ulceration in humans is a prominent medical condition, and there has long been pressure to develop effective and convenient ways to control it. Until recently, neutralizing stomach acid by pouring alkaline solutions (i.e., Alka Seltzer, Tums, Rolaids, etc.) into the stomach was the treatment. In fact, ulceration is a complicated process and not so easily solved.

Control of stomach acidity is a very important factor in the treatment of stomach ulcers. Unfortunately, the acid needed to digest food contributes to the creation of ulcers and perpetuating them. Cutting back stomach acid is important if an ulcer is to heal, and to accomplish this, an understanding of what causes the stomach to secrete acid is needed. It turns out there are three chemical signals that tell the stomach to secrete acid: gastrin (a hormone secreted when food is perceived in the stomach), acetylcholine (a neurotransmitter), and histamine (the same substance responsible for the unpleasant effects of allergy). There are numerous antihistamines on the market, but a special antihistamine is needed to work on the stomach.

Happily, famotidine is the right kind of antihistamine as are its cousins cimetidine (Tagamet® HB) and ranitidine (Zantac®). This class of antihistamines is not useful in combating familiar allergic symptoms (itching, sneezing, stuffy nose, etc.). In allergies, histamine causes unpleasant effects by binding so-called H1 receptors. In the stomach, histamine binds to H2 receptors to make stomach acid. Famotidine, cimetidine, and ranitidine are all H2 receptor blockers.

Famotidine is currently available in an over-the-counter formulation, making it highly convenient for pet owners to obtain (though obviously, you should not consider using medications licensed for human consumption without specific instructions from your pet's veterinarian).

Famotidine acts very quickly to reduce stomach acid, so it might be especially useful in an acute setting, though as technology has advanced, H2 receptor blockers are gradually becoming supplanted by proton pump inhibitors (such as omeprazole), which are even stronger antacids.

Famotidine has reduced effectiveness after about two weeks of use and is best used for conditions expected to resolve within that time frame.

How This Medication Is Used

Famotidine is useful in any situation where stomach irritation is an issue and ulceration is a concern. It is often used in the treatment of canine parvovirus, after ingestion of a toxin that could be ulcerating (overdose of aspirin, for example), any disease involving protracted vomiting, or in combination with other medications that may have stomach irritating properties so as to mitigate those properties.

In diseases involving frequent vomiting or regurgitation, the esophagus (the tube connecting the mouth and stomach) can be ulcerated by continuing exposure to vomit and stomach acid. Antacids are also helpful in this type of situation to reduce damage to the esophagus. Megaesophagus would be a condition where a long-acting antacid such as famotidine could be helpful in mitigating injury to the esophagus; however, there is a trade-off in protection against aspiration pneumonia, in that stomach acid hampers bacterial growth should stomach contents enter the lung.

Famotidine is directly helpful in managing nausea in species where there are H1 receptors in the brain's chemoreceptor trigger zone (an area involved in stimulating vomiting). In other words, famotidine is not only an antacid but also an antinauseal for dogs, but for cats is only an antacid.

Famotidine is given once or twice daily. If a dose is accidentally skipped, simply give it when you remember.  Do not double up on the next dose, but the broad safety range of this medication allows for leeway in the spacing of doses. 

Famotidine works best when given before the first meal of the day but can be given with or without food. Famotidine loses its power with long term use (over 14 days).

Side Effects

The H2 blockers as a group have a limited potential for side effects, hence their recent release to over-the-counter status.

Interactions With Other Drugs

Antibiotics of the cephalosporin class (particularly cefpodoxime) may not work as well when given with famotidine. It is best to separate their administration by at least 2 hours.

Some drugs are better absorbed in the presence of stomach acid (examples: itraconazole, ketoconazole, fluconazole, and oral iron supplements). These drugs should be given at least an hour apart from famotidine.

Cefpodoxime is not as well absorbed in the presence of famotidine. Giving both medications with food reduces this effect.

Oral iron supplements do not absorb into the body as well in the presence of famotidine. Stagger their administration by at least an hour.

Concerns and Cautions

It appears that famotidine is safe for use in pregnancy.

Famotidine tablets should be stored at room temperature and protected from light.