About trimethoprim
Antibiotic; dihydrofolate reductase inhibitor
Used for
- Treatment of uncomplicated urinary tract infections caused by susceptible bacteria.
Usual adult dose
Commonly 200 mg twice daily for 3 days for uncomplicated urinary infections; duration varies by indication.
Usual dose in children
For children aged 6 months and older, dosing is weight-based, commonly 4 mg/kg twice daily; maximum 200 mg per dose.
Common side effects
- Nausea, vomiting, or diarrhea
- Skin rash or itching
- Raised potassium levels
- Changes in blood cell counts
Important warnings
- Avoid with significant folate deficiency or certain blood disorders unless prescribed with monitoring.
- Kidney impairment may require dose adjustment.
- Seek urgent care for severe rash, breathing difficulty, or facial swelling.
- Use only when infection is likely or confirmed susceptible.
Pregnancy
May affect folate metabolism, especially early in pregnancy; use requires clinician assessment and may call for folic acid supplementation.
Breastfeeding
Generally compatible with breastfeeding a healthy, full-term infant; extra caution is needed for premature, jaundiced, or ill infants.
Interactions
- Warfarin: may increase bleeding risk; monitoring may be needed.
- Methotrexate: increased risk of blood toxicity.
- ACE inhibitors, ARBs, or spironolactone: increased risk of high potassium.
- Phenytoin: may increase phenytoin 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 It may be incomplete or out of date.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.