By Rania Gollakner, BS, DVM, MPH

What is sulfasalazine?

Sulfasalazine (brand names: Azulfidine®, Sulfazine®, Salazopyrin®) is a sulfonamide antibacterial and immunosuppressive medication used to treat inflammatory large bowel disease, as well as for vasculitis in dogs.  

Its use in cats, dogs, ferrets, and horses to treat inflammatory large bowel disease or vasculitis is ‘off label’ or ‘extra label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

How is sulfasalazine given?

Sulfasalazine is given by mouth in the form of a tablet. Give this medication with food. Handle this medication with caution if you have a known allergy to sulfa drugs; wearing gloves is recommended and be sure to wash your hands after administering. This medication should take effect within 1 to 2 hours, and while effects may not be visibly obvious, gradual improvements are usually noticeable after a few days.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects include decreased appetite, vomiting, yellowing of the skin, eyes, or body fluids. In cats, lack of appetite, vomiting, and anemia are possible. Serious side effects include dry eye/keratoconjunctivitis sicca (KCS) which will appear as squinting, mucoid eye discharge, and eye discomfort. Other serious side effects include lack of energy, persistent vomiting, diarrhea, lack of appetite, paleness, fever, and skin rashes.

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?

Sulfasalazine should not be used in pets that are allergic to it or other sulfonamides or salicylates. It should not be used in Doberman Pinschers, Miniature Schnauzers, or Samoyeds, or in pets with dry eye/KCS, intestinal or urinary blockages, or severe dehydration.

Sulfasalazine should be used cautiously in pets with liver, kidney, or blood diseases, or in pets that are pregnant or nursing. Use cautiously in cats, or in sensitive dog breeds such as Cocker Spaniels, Bulldogs, West Highland Terriers, Lhasa Apsos, or Shih Tzus.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with sulfasalazine: antibacterial agents, chlorpropamide, cyclosporine, digoxin, ferrous sulfate and other iron salts, folic acid, or warfarin.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Your veterinarian may monitor your pet to be sure that the medication is working. Your veterinarian may monitor for KCS/dry eye, by performing a tear test prior to starting therapy and rechecking regularly during therapy. In the case of long-term therapy, your veterinarian may regularly monitor blood cell counts and liver panels. Monitor your pet at home for side effects.

How do I store sulfasalazine?

Store the tablets at room temperature, preferably between 68°F and 77°F (20°C and 25°C); do not exceed 104°F (40°C). Protect from light.

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.

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