Trimethoprim/Sulphonamide

Trimethoprim/Sulphonamide In Dogs & Cats: Uses, Dosage and Side Effects

Overview

• Trimethoprim and sulphonamides work together to block sequential steps in the synthesis of tetrahydrofolate, which is essential for the synthesis of various molecules, including nucleic acids.
• This two-step mechanism helps slow down the development of bacterial resistance compared to using either agent alone.
• Their mechanism of action is time-dependent.

Uses of Trimethoprim/Sulphonamide

• Trimethoprim/sulphonamide is effective against various organisms, including Nocardia, Brucella, some Gram-negative bacilli, Streptococcus, Pneumocystis carinii, Toxoplasma gondii, and other coccidians.
• However, Pseudomonas and Leptospira are typically resistant to this combination.
• It is useful for managing urinary, respiratory tract, and prostatic infections but ineffective in necrotic tissue.
• Trimethoprim alone can be used for urinary, prostatic, systemic salmonellosis, and respiratory tract infections, with fewer adverse effects compared to the combination.
• Trimethoprim is a weak base that gets trapped in fluids more acidic than plasma (e.g., prostatic fluid and milk).
• Patients receiving sulphonamides should be well hydrated and avoid urinary acidifying agents.

Dose of Trimethoprim/Sulphonamide in Dogs and Cats

Dogs, Cats:

• 15–30 mg/kg p.o. q12h. 30 mg/kg s.c. q24h.
• Doses (mg) of total product (trimethoprim + sulphonamide).

Side Effects of Trimethoprim/Sulphonamide in Dogs and Cats

• Cats may exhibit drowsiness, anorexia, leucopenia, anemia, and hypersalivation.
• Dogs may experience hepatic necrosis, vomiting, immune-mediated thrombocytopenia, and immune-mediated polyarthritis.
• Dobermanns appear to be more prone to developing immune-mediated systemic adverse effects.
• Acute hypersensitivity reactions, such as type III hypersensitivity reactions, are possible with sulphonamide products.
• Sulphonamides can reversibly suppress thyroid function.
• Keratoconjunctivitis sicca (KCS) has been reported in dogs treated with sulfapyridine and other sulphonamides. Therefore, monitor tear production, especially during long-term use and in breeds susceptible to KCS.

Contraindications of Trimethoprim/Sulphonamide in Dogs and Cats

• Avoid use in animals with keratoconjunctivitis sicca (KCS) or previous history of adverse reaction to sulphonamides such as KCS or polyarthritis.

Some Notes:

• Antacids may reduce the absorption of sulphonamides when taken together.
• Urinary acidifying agents can increase the risk of sulphonamide crystal formation in the urinary tract.
• Concurrent use of drugs containing procaine might hinder the effectiveness of sulphonamides since procaine acts as a precursor for para-amino benzoic acid.