About trimethoprim
Antibiotic; dihydrofolate reductase inhibitor
Used for
- Treats urinary tract infections caused by susceptible bacteria.
- Sometimes used to prevent recurrent urinary tract infections.
Usual adult dose
For uncomplicated urinary infections, usually 200 mg twice daily for 3 days; duration varies by infection.
Usual dose in children
For urinary infections, typically 4 mg/kg twice daily, up to 200 mg per dose; age and treatment duration vary.
Common side effects
- Nausea or vomiting
- Diarrhea
- Rash or itching
- Raised potassium or changes in blood counts, especially with prolonged use
Important warnings
- Not suitable for some people with severe kidney or liver problems.
- Can rarely cause serious blood disorders or severe skin reactions.
- May not work against bacteria that are resistant to trimethoprim.
- Dose and duration depend on infection, kidney function, and local guidance.
Pregnancy
Usually avoided in early pregnancy unless a clinician considers it necessary; it can interfere with folate metabolism.
Breastfeeding
Generally considered compatible with breastfeeding a healthy full-term infant; extra caution is needed for premature or jaundiced infants.
Interactions
- Warfarin: may increase bleeding risk.
- Methotrexate: may increase toxicity, including blood disorders.
- Phenytoin: may increase phenytoin levels.
- Potassium-raising medicines, including ACE inhibitors and spironolactone: may increase potassium levels.
AI-generated from general medical knowledge, not from this product's official leaflet. It may be incomplete or out of date. Not medical advice — ask a pharmacist or doctor before making any decision.