Mar Vista Animal Medical Center

3850 Grand View Blvd.
Los Angeles, CA 90066




(for veterinary information only)




75 mg TABLETS,
150 mg TABLETS,
300 mg TABLETS



Stomach ulceration in humans is a prominent medical condition and there has long been pressure to develop effective and convenient ways to address it. Until relatively recently, we relied on simply neutralizing stomach acid by pouring alkaline solutions (ie alka seltzer, Tums, Rolaids etc.) into the stomach. This was a temporary and often incomplete solution to an on-going stomach acid problem. In fact, stomach ulceration is a complicated process and more sophisticated treatments have become available.

Controlling stomach acid remains an important part of treating and preventing stomach ulcers. Acid secretion by the parietal cells of the stomach is stimulated by three main things: gastrin (a hormone secreted when there is food in the stomach to digest), acetylcholine (a neurotransmitter) and histamine (the same histamine that is involved in allergy).

There are two types of histamine receptors in the body: H1 receptors which are involved in the symptoms of "hay fever" and H2 receptors which are located in the stomach and turn on stomach acid secretion. Ranitidine is a special antihistamine, as are its cousins cimetidine (Tagamet HB®) and famotidine (Pepcid AC®). These medications are not useful in combating allergic symptoms where histamine causes its unpleasant effects by binding so-called “H1” receptors; instead they bind to histamine receptors in the stomach called “H2” receptors and control stomach acid secretion.

Cimetidine was the first such “H2 blocker” available and each generation has brought about improvements in terms of fewer drug interactions and stronger effect. Ranitidine offers an additional benefit in that not only does it act as an effective antacid but it also aids in encouraging normal stomach contractions. When it comes to managing nausea, normal stomach contractions are crucial in preventing the pooling of food in the stomach. Stomach distension is a stimulus for vomiting. Ranitidine helps with nausea by addressing both stomach acid and stomach contractions. As an antacid, Ranitidine is between 3 and 13 times stronger than its predecessor cimetidine.



Ranitidine is useful in any situation where stomach irritation is an issue and ulceration is a concern. It is often used in the treatment of Helicobacter infection, inflammatory bowel disease, canine parvovirus, kidney failure, ingestion of a toxin that could be ulcerating (over dose of aspirin, for example), any disease involving protracted vomiting, or chronically in combination with medications which may have stomach irritating properties.

In diseases involving frequent vomiting or regurgitation, the esophagus (tube connecting the mouth and stomach) can be ulcerated by continuing exposure to vomit/stomach acid. Antacids are also helpful in this type of situation to reduce damage to the esophagus.

Ranitidine is generally used twice a day and can be used long term. If a dose is accidentally skipped, give it when it is remembered and time the next dose accordingly. Do not double up on the next dose.

Ranitidine works best if given before the first meal of the day.




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

Occasionally humans report headache or mental confusion.



Medications that do not work as well in the presence of ranitidine: Ketoconazole, itraconazole, and fluconazole (all antifungals) are not absorbed into the body as well when the stomach is less acid. Ideally they should be given an hour prior to the ranitidine. Cefpodoxime (an antibiotic) is not absorbed as well with concurrent use of ranitidine but giving the cefopodoxime with food can mitigate this.



  • The dose of ranitidine may require reduction in patients with liver or kidney disease as these diseases tend to prolong drug activities.
  • It appears that ranitidine is safe for use in pregnancy but should probably be avoided during lactation.
  • The use of ranitidine can cause a urine dipstick to falsely test positive for protein.


Short version (to help us comply with "Lizzie's Law")

Page last updated: 7/25/2020