Trimethoprim for Cats

Is it time for my medication?
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If Kitty has adverse reactions such as diarrhea to certain antibiotics, your vet might prescribe the broad-sprectrum drug trimethoprim. Unlike some other antibiotics, it does minimal harm to the good bacteria in Kitty's intestinal tract. There's also an advantage for your wallet -- it's relatively inexpensive.


Trimethoprim is marketed under the brand name Tribrissen by Merck Animal Health. For use in humans it's sold under the names Bactrim, Cotrim, Sulfatrim and Septra.

Each of these medications also contains sulfamethoxazole, another antibiotic. The two drugs work well in conjunction with each other to rid pets and people of infections. Together, they kill bacteria in different ways -- by destroying bacteria's proteins and nucleic acids and by preventing their replication. They can penetrate the blood/brain barrier and other areas that many antibiotics can't.

Trimethoprim is available as pills and as injections.


In cats, trimethoprim might be prescribed to treat respiratory or gastrointestinal infections. If Kitty develops an abscess -- for instance, after fighting with another cat -- your vet might prescribe the drug to combat or prevent an infection. It's prescribed for both bacterial and protozoal infections, such as coccidiosis.

Feline Kennel Cough

Your might think kennel cough is strictly for dogs. But although it occurs more regularly in dogs, cats aren't immune. It's extremely contagious and can quickly infect cats living in crowded conditions, such as at animal shelters or boarding facilities. One of trimethoprim's primary uses in cats is getting rid of the Bordatella bronchiseptica bacteria that causes the disease.

If Kitty has recently been in an environment with a lot of strange cats and starts sneezing and coughing, kennel cough could be the culprit. Take him to the vet for diagnosis and treatment.

Side Effects and Contraindications

Trimethoprim has relatively few side effects, and it's generally safe and effective in felines. It shouldn't be given to pregnant or lactating cats. If Kitty suffers from kidney disease or has had kidney stones in the past, he should be given a different antibiotic. It's also a no-no for cats with liver or blood problems. If your vet suspects Kitty has thyroid issues, he can't be tested until after he's through with the medication.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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