Major Uses

Sulfadimethoxine is a sulfonamide antibiotic that kills bacteria by interfering with reproduction. The drug is generally used in combination with other medications, such as trimethoprim or ormetoprim, but is sometimes used alone in the treatment of infections with certain intestinal parasites.

Sulfadimethoxine is indicated for the treatment of various enteric, respiratory, soft tissue, and genitourinary tract infections in cats and dogs. It generally works quickly and provides broad-spectrum coverage when combined with other drugs. It is very effective when treating coccidial infections in many animal species, including dogs and cats.

Common Precautions

Sulfadimethoxine may cause a variety of side effects, most of which occur rarely. Some of the more common adverse effects include joint inflammation, skin rash, inadequate tear production, and blood dyscrasias. If eye discharge, redness, or other symptoms develop, the medication should be stopped.

Less commonly, treatment with sulfadimethoxine can result in anemia and associated pale gums and tiredness. Low platelets, vomiting, diarrhea, and fever are also possible. Kidney damage is a rare but serious adverse effect that is sometimes seen.

Due to potentially harmful effects, sulfadimethoxine should not be administered to animals with kidney or liver disease, or to those experiencing dehydration or at increased risk for kidney or bladder stones. Animals with existing dry eye disease should only use this medication when absolutely necessary. Sulfadimethoxine is not safe for use during pregnancy. It should not be used in lactating animals.

Sulfadimethoxine may cause sulfa crystals to appear in the urine of animals undergoing treatment with the medication. This shows up on urinalysis, but is not a problem in animals that drink plenty of fluids.

The drug is known to interact with numerous other medications and supplements, including methotrexate, probenecid, phenylbutazone, salicylates, warfarin, thiazide diuretics, phenytoin, and antacids.

Sulfadimethoxine should not be used in animals with a known allergy or hypersensitivity to the drug. Signs of sulfadimethoxine overdose are similar to reported side effects. Behavior changes may also occur. Any known or suspected overdose should be reported to a veterinarian right away.


Sulfadimethoxine should be stored in its original packaging, at room temperature, and away from children and animals. It should be kept away from light sources.


Sulfadimethoxine is available as an oral suspension and as tablets in strengths of 124 mg, 250 mg, and 500 mg.

Following an initial dose of 25 mg/lb (55 mg/kg) of body weight, sulfadimethoxine is typically dosed at 12.5 mg/lb (27 mg/kg) of body weight once every 24 hours. Treatment generally continues for 3 to 5 days.

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 sulfadimethoxine 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.