Cat · Felis catus · typical adult weight 2.50–7.00 kg
Trimethoprim-Sulfamethoxazole is dosed at 15–30 mg/kg PO q12h in cats, per Weese JS, Blondeau J, Boothe D, et al. International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. Vet J. 2019;247:8-25. doi:10.1016/j.tvjl.2019.02.008 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.1223 (2026-08-01).. Trimethoprim-Sulfamethoxazole is used in cats for Nocardia infections, Bacterial infections when oral not feasible, Pneumocystis (immunocompromised), UTI, skin infections, toxoplasmosis. Routes documented in cats: PO. A typical adult cat weighs 2.50–7.00 kg. ExoticRx lists 4 cited dose rules for Trimethoprim-Sulfamethoxazole in cats, drawn from published veterinary references. Verify against current literature before clinical use.
US trade names: Bactrim, TMS
| Route | Dose | Frequency | Duration | Indication | Evidence | Source |
|---|---|---|---|---|---|---|
| PO | 15–30 mg/kg | q12h | 6-12 weeks | Nocardia infections | Moderate | Weese JS, Blondeau J, Boothe D, et al. International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. Vet J. 2019;247:8-25. doi:10.1016/j.tvjl.2019.02.008 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.1223 (2026-08-01). |
| PO | 15–30 mg/kg | q12h | Until oral feasible | Bacterial infections when oral not feasible | Moderate | Plumb's Veterinary Drug Handbook, 9th Ed, p.1223 (Sulfa-/Trimethoprim, Dosages, CATS); corroborated by BSAVA Small Animal Formulary 10th Ed Part A p.419 'Dogs, Cats: 15-30 mg/kg p.o. q12h' |
| PO | 15–30 mg/kg | q12h | 21 days | Pneumocystis (immunocompromised) | Weak | Weese JS, Blondeau J, Boothe D, et al. International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. Vet J. 2019;247:8-25. doi:10.1016/j.tvjl.2019.02.008 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.1223 (2026-08-01). |
| PO | 15–30 mg/kg | q12h | 14-21 days | UTI, skin infections, toxoplasmosis | Strong | Weese JS, Blondeau J, Boothe D, et al. International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. Vet J. 2019;247:8-25. doi:10.1016/j.tvjl.2019.02.008 — Verified against Plumb's Veterinary Drug Handbook, 10th Ed, p.1223 (2026-08-01). |
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These ranges are per kg. Enter your cat's weight to get the precise dose and draw-up volume — unit and concentration math done for you.
Sequential blockade of folate synthesis: sulfamethoxazole inhibits dihydropteroate synthase; trimethoprim inhibits dihydrofolate reductase.
May cause keratoconjunctivitis sicca (KCS) in dogs with prolonged use. Can cause bone marrow suppression. Avoid in animals with hepatic disease. Adequate hydration required.
Species-specific contraindications and adverse-reaction reports for cats may differ from canine / feline reference data — consult the primary citations listed with each rule.
Trimethoprim-Sulfamethoxazole dose ranges in cats, with cited source references: PO 15–30 mg/kg q12h; PO 15–30 mg/kg q12h; PO 15–30 mg/kg q12h; PO 15–30 mg/kg q12h. Reference ranges from cited sources — verify against current literature before clinical use.
Documented routes for Trimethoprim-Sulfamethoxazole in cats: PO.
Cited course lengths for Trimethoprim-Sulfamethoxazole in cats include: 6-12 weeks; Until oral feasible; 21 days; 14-21 days. Duration depends on the indication — match it to the specific dose rule in the table above.
Trimethoprim-Sulfamethoxazole is indicated in cats for: Nocardia infections, Bacterial infections when oral not feasible, Pneumocystis (immunocompromised), UTI, skin infections, toxoplasmosis.
These are general warnings for Trimethoprim-Sulfamethoxazole across species; consult the cat dosing table above for species-specific guidance. May cause keratoconjunctivitis sicca (KCS) in dogs with prolonged use. Can cause bone marrow suppression. Avoid in animals with hepatic disease. Adequate hydration required.
Why a species-specific page? Trimethoprim-Sulfamethoxazole pharmacokinetics differ across species: dose ranges, intervals, and route preferences are not interchangeable. Cross-extrapolation from canine doses is unsafe in cats — the rules above are the citations specific to this species, not generic recommendations.
Sourced from published veterinary references; awaiting credentialed clinical reviewer. See our editorial process. Reference only — not veterinary advice.