Cimetidine

What is cimetidine?

Cimetidine (brand name: Tagamet®) is an over-the-counter histamine2 (H2) blocker. Because it reduces acid production in the gastrointestinal tract, cimetidine may be recommended to treat or prevent stomach, esophageal, or intestinal ulcers or inflammation.

These conditions may occur without an identified cause or may be secondary to acid reflux, stress, drug reaction, or kidney disease.

Its use in cats, dogs, small mammals, and horses to treat stomach acid disorders is off label (extra label). Many drugs are commonly prescribed for off-label use in veterinary medicine. 

“Off label” means the drug is being used in a way that has not been reviewed or approved by the U.S. Food and Drug Administration (FDA) or Health Canada. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.

How is cimetidine given?

• Cimetidine is given by mouth in the form of a tablet or liquid solution. Do not switch forms of this medication without consulting your veterinarian as the dosages may be different.
• Measure liquid forms carefully.
• Give cimetidine about 30 minutes prior to a meal, usually in the morning.
• If vomiting occurs when dosed on an empty stomach, give future doses with a meal.

This medication should take effect within 1 to 2 hours, and improvements in clinical signs should follow.

What if I miss giving my pet the medication?

If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.

Are there any potential side effects?

Side effects are uncommon and are not well documented in animals. Side effects reported in humans, which may be seen in animals, include:

• Confusion
• Headache

In cats, drooling may occur due to the taste of the medication.

Other side effects may occur. If you notice anything unusual, contact your veterinarian immediately. This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

DO NOT USE cimetidine in pets that:

• Are allergic to it or other H2 blockers

USE WITH CAUTION in pets that:

• Are geriatric
• Have liver or kidney dysfunction
• Are pregnant and/or lactating pets (safety has not been established)

Are there any drug interactions I should be aware of?

Several medications should be used with caution when given with cimetidine, including:

• Antacids
• Benzodiazepines
• Beta- blockers
• Calcium channel blockers
• Certain antibiotics and antifungals, including cefpodoxime, chloramphenicol, itraconazole, ketoconazole, etronidazole, terbinafine
• Cisapride
• Clopidogrel
• Cyclosporine
• Lidocaine
• Loratadine
• Mirtazapine
• Myelosuppressive drugs
• Opioids
• Pentoxifylline
• Praziquantel
• Sildenafil
• SSRIs
• Tamsulosin
• Theophylline
• Tolazoline
• Triamterene
• Tricyclic antidepressants

This medication may also interfere with certain laboratory tests such as allergen skin tests; discontinue this medication at least 24 hours prior to these tests.

Certain medications may interact with cimetidine, so be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking before starting any new treatment.

Is any monitoring needed with this medication?

• Your veterinarian will let you know when and how they want to reassess your pet to ensure the medication is working and not causing side effects.
• At home, monitor for any side effects such as those noted above. If any occur, stop using the medication and contact your veterinarian.

How do I store cimetidine?

• Store the tablet form of this medication at room temperature and protected from light and moisture.
• For the liquid form of medication, follow the directions on the bottle.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility. Be prepared to provide information about the product and your pet’s weight and symptoms.