Major Uses

Trimethoprim with sulfamethoxazole is a combination of two antibiotics that is commonly used in both dogs and cats to treat various infections such as urinary tract infections, enteritis, otitis media, pneumonia, prostatitis, kennel cough, staphylococcal, and coccidiosis.

Common Precautions

Pregnant animals should not be exposed to trimethoprim with sulfamethoxazole, as complications may arise. If the patient is taking other drugs, a veterinarian should be consulted to make sure that there are no conflicts between prescriptions. Animals with dehydration, severe liver or kidney disease, or bladder or kidney stones should not take this drug. It should be administered cautiously in patients with anemia or other blood cell disorders.

Some negative side effects associated with trimethoprim with sulfamethoxazole include sulfa crystals in the patient's urine and keratoconjunctivitis sicca, which is characterized by redness of the eye, squinting, and discharge from the eye. Other possible side effects are anemia, tiredness, diarrhea, vomiting, loss of appetite, fever, joint inflammation, kidney damage, liver damage, and skin rashes.

Trimethoprim with sulfamethoxazole should not be used in animals with a known allergy or hypersensitivity to the drug. A veterinarian should be contacted immediately if an overdose is suspected, the symptoms of which include depression, facial swelling, and confusion.


Trimethoprim with sulfamethoxazole should be kept at room temperature and stored in a childproof, light resistant container. It should be carefully kept out of the reach of children and pets.


Trimethoprim with sulfamethoxazole is typically administered in doses of 25-100 mg/kg depending on what it is being used to treat. It is administered once every 24 hours and can be administered as a tablet, oral paste, or injection. Treatment usually lasts from 10-20 days. In a case where a dose is forgotten, it should be administered as soon as possible. If it is nearing time for the next scheduled dose, the missed dose should be skipped and the regular administration schedule should resume. Two doses should not be given at the same time.

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.

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.