Trimethoprim
AntibioticsAn antibiotic that inhibits dihydrofolate reductase (DHFR), disrupting the folic-acid pathway required for bacterial DNA synthesis. It is usually combined with a sulfonamide (potentiated sulfonamide), producing a synergistic sequential blockade that is bactericidal and broad-spectrum.
Pharmacological information
A class-level scientific overview for general reference — no doses. The ultimate reference is always the locally approved product leaflet and consultation with a veterinarian.
Mechanism of action
An antibiotic that inhibits dihydrofolate reductase (DHFR), disrupting the folic-acid pathway required for bacterial DNA synthesis. It is usually combined with a sulfonamide (potentiated sulfonamide), producing a synergistic sequential blockade that is bactericidal and broad-spectrum.
Indications
- Respiratory, urinary, gastrointestinal, and skin infections caused by susceptible bacteria (as a potentiated sulfonamide)
Contraindications & warnings
- Hypersensitivity to sulfonamides (in the combination product)
- Caution in hepatic or renal impairment and bone-marrow disorders with prolonged use
- May be associated with dry eye (keratoconjunctivitis sicca) in dogs
Drug interactions
- Synergy with sulfonamides (the therapeutic basis of the combination)
- May increase the effect of some anticoagulants and other highly protein-bound compounds
Prudent use of antibiotics
Prescribed based on diagnosis and susceptibility testing where possible, to limit antibiotic resistance.
Withdrawal periods
| Species | Meat | Milk | Eggs |
|---|---|---|---|
| Cattle | 12 days | 2 days | — |
| Horses | — | — | — |
| Species | Meat | Milk | Eggs |
|---|---|---|---|
| Horses | — | — | — |
| Species | Meat | Milk | Eggs |
|---|---|---|---|
| Chickens | 6 days | — | — |
| Species | Meat | Milk | Eggs |
|---|---|---|---|
| Chickens | 5 days | — | — |
| Species | Meat | Milk | Eggs |
|---|---|---|---|
| Cattle | 12 days | 2 days | — |
| Species | Meat | Milk | Eggs |
|---|---|---|---|
| Chickens | 5 days | — | — |
| Species | Meat | Milk | Eggs |
|---|---|---|---|
| Rabbits | — | — | — |
| Species | Meat | Milk | Eggs |
|---|---|---|---|
| Cattle | 10 days | 60 hours | — |
| Horses | — | — | — |
Recorded adverse effects
openFDA veterinary reports — the numbers are report counts, not a severity rate.
Related products
Sources
- •Withdrawal periods: UK Veterinary Medicines Directorate (VMD).
- •European Medicines Agency (EMA) — Veterinary medicines
- •Merck Veterinary Manual — Pharmacology
- •World Organisation for Animal Health (WOAH) — Prudent use of antimicrobials
- •Always verify the locally approved leaflet and consult a veterinarian.