Major Uses

Sulfasalazine is a sulfanomide antibiotic that has been bonded to a salt of salicylic acid. It is used primarily for its anti-inflammatory effects on the colon and works by reducing production of inflammatory cytokines and eicosanoids and by inhibiting prostaglandin, a hormone-like compound involved in inflammation. Sulfasalazine is an effective treatment for colitis and other inflammatory bowel diseases and helps control associated diarrhea and other symptoms.

Sulfasalazine is not approved by the Food and Drug Administration for use in animals, but it is prescribed legally as an extra-label drug by veterinarians. It is most often prescribed for use in dogs, but the drug is also used in cats.

Common Precautions

Sulfasalazine is associated with several uncommon, but potentially serious side effects. In some cases, the drug may trigger an inflammatory syndrome that causes fever, arthritis, muscle soreness, eye inflammation, and kidney inflammation. These symptoms typically clear up about one week after stopping the medication.

The drug may also cause skin rash, poor tear production, and blood dyscrasias, which are abnormal blood cells. Hepatitis and liver failure are also possible and can lead to death. Jaundice and nausea are often the first symptoms associated with liver failure caused by sulfasalazine. Other possible side effects include Heinz body anemia, itching, urticaria, and liver or kidney damage.

Because cats are especially sensitive to salicylates, sulfasalazine should be used cautiously in felines and adjustments to dosing may be necessary. Male fertility may be negatively affected by the drug. This should be noted before beginning treatment. Sulfasalazine is not for use during pregnancy. Animals suffering from porphyria or intestinal or urinary tract obstruction should not be given sulfasalazine. Those with fever, severe allergy, jaundice, liver disease, kidney disease, blood dyscrasias, or low Schirmer tear test results should use the drug cautiously or not at all.

In cases of inflammation and/or ulceration of the intestinal wall, only enteric-coated sulfasalazine should be administered. Otherwise, vomiting, anorexia, diarrhea, and gastric distress may develop.

Sulfasalazine may interact with a variety of supplements and medications, including protein-bound drugs. Methotrexate, phenytoin, phenobarbital, iron supplements, antacids, warfarin, aspirin, thiazide diuretics, digoxin, folic acid, and sulfonylureas are all known to interact with sulfasalazine.

Sulfasalazine should not be used in animals with a known allergy or hypersensitivity to the drug. Any known or suspected overdose should be reported to a veterinarian right away.


Sulfasalazine should be stored in a tightly-sealed container, at room temperature, and away from children and animals.


Sulfasalazine is available as an oral suspension and as 500 mg tablets. In dogs, sulfasalazine is typically dosed at 10 to 25 mg/lb (20 to 50 mg/kg) every 8 hours for as long as 3 to 6 weeks. In cats, the typical dose is 5 to 10 mg/lb (10 to 20 mg/kg) every 12 to 24 hours.

Doses may vary in different species, when the drug is given by a different route or concurrently with other medications, and with regards to a patient's age, breed, and health status. A veterinarian's dosing instructions and/or those printed on the medication label should be followed closely.

If a dose of sulfasalazine is missed, it should be given as soon as possible. If it is almost time for the next dose, the missed dose should be skipped and the normal schedule resumed. Two doses of this medication should not be given at once.

This information is for general reference only and should not be used for the diagnosis or treatment of any condition of your pet. It's intended as a general reference, this information may not include all possible uses, precautions, directions, reactions (including allergic), drug interactions, or withdrawal times. Always consult your local veterinarian and have your pet examined for any advice concerning the diagnosis and treatment of your pet, including which products and doses are most appropriate. Any trademarks are the property of their respective owners. VetDepot is not a pharmacy. All prescription products are dispensed by our Pharmacy Partner. Article last updated 2/2014.