Cotrimoxazole
Tablet or syrup
Quick Summary
Cotrimoxazole combines two antibiotics that block bacteria from making folic acid.
Medical Uses
How it's taken
Drink plenty of fluids while taking it.
Take it for the full course, even if you feel better, unless your doctor tells you otherwise. Don't share antibiotics or keep leftovers.
Your doctor decides the right dose for you and how long to take it.
Your doctor decides the right dose for you. Follow their instructions and the label.
Common Side Effects
Nausea
And loss of appetite.
Rash
Stop and see a doctor.
Blood changes
With longer use.
Interactions
Warfarin
Bleeding risk.
Methotrexate
Toxicity risk.
Potassium-raising medicines
High potassium.
Critical Warnings
Severe skin reactions
Black Box Warning: Stop immediately for a blistering rash or mouth sores.
Sulfa allergy
Don't take if allergic to sulfa medicines.
Severe allergic reaction
Black Box Warning: Swelling of the face or throat, difficulty breathing or a widespread rash: get emergency help.
Antibiotic resistance
Using antibiotics when they aren't needed makes them less effective for everyone.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Co-trimoxazole: drug information(opens in a new tab) · MedlinePlus, US National Library of Medicine