Trimethoprim
What it's for
Trimethoprim is an antibiotic for urinary tract infections (UTIs) and cystitis. It kills the bacteria causing the infection. A short course usually clears the infection.
Comes as: Tablets or liquid
How to take it
- Adults: Usually 200mg twice daily for 3 days.
- Or 100mg twice daily for 7 days.
- Take with or without food.
- Complete the full course.
Doses here are typical. Always follow the instructions from your prescriber or on the packet — they come first.
Common side effects
- Feeling sick
- Diarrhoea
- Headache
- Itching or skin rash
The leaflet inside the packet lists all known side effects.
Important safety points
- Not suitable in pregnancy, especially first trimester
- Tell your doctor if you have kidney problems
- Can interact with methotrexate - avoid taking together
- Can affect blood tests for folate levels
Get medical help urgently if…
- You develop a severe skin rash or blistering
- You have a sore throat, fever, or mouth ulcers
- You have unusual bruising or bleeding
- You have severe stomach pain
Call NHS 111 for urgent advice, or 999 if someone is seriously unwell.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.