Overview of Trimethoprim + Sulfadiazine for Canines and Felines
- Trimethoprim is an effective antibiotic that becomes even more effective when combined with a sulfonamide (sulfa drug), such as sulfadiazine and sulfamethoxazole. The combination, better known as Tribrissen®, exhibits a greater spectrum of activity against microorganisms that cause infectious disease for dogs and cats. The addition of trimethoprim to a sulfa drug forms a potentiated sulfa.
- Trimethoprim plus sulfadiazine and trimethoprim plus sulfamethoxazole are the most often-used combinations in veterinary medicine. These are similar in antibiotic function and may be used interchangeably.
- Trimethoprim-sulfa can kill a variety of bacteria. An additional effect of potentiated sulfa drugs is an ability to kill or suppress certain intracellular parasites, particularly Coccidia spp. and the microorganism responsible for the disease Toxoplasmosis.
- Trimethoprim/sulfadiazine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
Brand Names and Other Names of Trimethoprim/Sulfadiazine
- This drug is registered for use in humans and animals.
- Human formulations: Proloprim® (Glaxo Wellcome), Septra® (Glaxo Wellcome), Bactrim® (Roche) and various generic preparations
- Veterinary formulations: Tribrissen® (Schering) and various generic preparations
Uses of Trimethoprim/Sulfadiazine for Dogs and Cats
- Trimethoprim/sulfadiazine is used in dogs and cats to treat infections likely to be susceptible to the drug.
- Trimethoprim/sulfadiazine has also been used to treat parasitic infections caused by the microorganisms toxoplasmosis and coccidia (an intestinal parasite).
Precautions and Side Effects
- While generally safe and effective when prescribed by a veterinarian, trimethoprim/sulfadiazine can cause side effects in some animals.
- Trimethoprim/sulfadiazine should not be used in animals with known hypersensitivity or allergy to the drug.
- Trimethoprim/sulfadiazine should be avoided in animals with liver impairment or blood disorders.
- Due to the potential for injury to the fetus, trimethoprim/sulfadiazine should be avoided in pregnant animals.
- Some important adverse effects associated with trimethoprim/sulfadiazine include dry eye (keratoconjunctivitis sicca), liver inflammation, vomiting, lack of appetite, diarrhea, fever, facial swelling, arthritis and blood disorders such as hemolytic anemia or low platelet counts. Dry eye can be especially important and some veterinarians will measure tear production before and during treatment with the drug, especially if long-term treatment is indicated.
- Trimethoprim/sulfadiazine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with Trimethoprim/sulfadiazine.
- With prolonged administration, potentiated sulfa drugs have been associated with abnormal thyroid tests and possibly with hypothyroidism in dogs.
How Trimethoprim/Sulfadiazine Is Supplied
- Trimethoprim/sulfadiazine is available in 30 mg, 120 mg, 480 mg and 960 mg tablets.
- A 400 mg oral paste is also available.
- Trimethoprim/sulfamethoxazole is available in injectable form.
Dosing Information of Trimethoprim/Sulfadiazine for Dogs and Cats
- Medication should never be administered without first consulting your veterinarian.
- In dogs and cats, trimethoprim/sulfadiazine is typically dosed at 7 to 15 mg per pound (15 to 30 mg/kg) one to three times daily.
- Alternative dosing may be indicated in some dogs treated chronically with this drug.
- The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your dog or cat feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.