How Is Sulfasalazine Used for Dogs?

Sulfasalazine can cause side effects, so it is important that its use be supervised by your veterinarian.
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Your dog can develop diarrhea for a number of reasons; one of the medications that may be prescribed as a treatment is sulfasalazine. This medication is an anti-inflammatory and antibiotic medication that improves diarrhea after it breaks down into an active form in the colon. Sulfasalazine is available by prescription only, because it has the potential to cause side effects and may interact with other medications your dog is receiving.

How It Works

Regardless of the cause of diarrhea in your dog, inflammation is created in the intestine or colon by the underlying ailment. Sulfasalazine improves the condition primarily by decreasing inflammation in the large intestine, allowing the affected tissues to heal and decreasing the chance that diarrhea will continue. Sulfasalazine is not active until it is broken down in the large intestine by bacteria. Once this occurs, it forms two parts -- the more important anti-inflammatory component and an antibiotic component. The anti-inflammatory component is a derivative of aspirin and therefore works in the same way.


Since sulfasalazine is effective at reducing inflammation, it is used to treat other symptoms caused by diseases that create inflammation of the intestines, particularly the large intestine. Two of the most common diseases of dogs treated with sulfasalazine are inflammatory bowel disease and ulcerative colitis. Both of these conditions create large amounts of inflammation in the colon; the use of sulfasalazine can diminish the symptoms. Additionally, the drug can serve to treat any condition that may cause inflammation, such as gastritis from eating foreign material, radiation-induced colitis in dogs receiving radiation therapy, and severe bacterial overgrowth. It is important to realize that sulfasalazine is not a treatment for the underlying disease itself; it is simply treating the symptom of diarrhea. Therefore additional treatments would be recommended for the actual disease process.

Side Effects

Like any drug, sulfasalazine has the potential for side effects and therefore is available only by prescription. Possible side effects of sulfasalazine include loss of appetite, vomiting, facial swelling or a rash, and fever and jaundice due to liver effects. With long-term use, sulfasalazine can lead to dry eye due to development of a condition known as keratoconjunctivitis sicca.

Drug Interactions

If your dog is prescribed sulfasalazine, discuss other medications she is receiving with your veterinarian. While your dog is receiving sulfasalazine, she must not receive any other type of anti-inflammatory medication such as Rimadyl, corticosteroids such as prednisone, or aspirin. Dogs receiving digoxin for heart disease or phenobarbital for seizures should not take sulfasalazine. Sulfasalazine can also interact with azathioprine and blood-thinning medications. If your dog must take any of these medications with sulfasalazine, have her closely monitored by your veterinarian. Immediately report any suspected adverse reactions so the medication can be discontinued and appropriate treatment can be initiated.