• Proven antibiotic for cystitis, trusted for decades
  • Brings fast relief from burning, urgency, and discomfort
  • Alternative to nitrofurantoin, effective when first-line options aren’t suitable

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Overview

Burning, stinging, constant bathroom trips? Trimethoprim is a trusted antibiotic that clears cystitis fast.

By stopping bacteria from multiplying in the bladder, it gets to the root of the infection - easing pain, urgency, and discomfort within days. A reliable choice when you need quick relief and proven results.


What is Trimethoprim 


Cystitis (urinary tract infection) happens when bacteria enter and irritate the bladder, causing painful symptoms. Trimethoprim is one of the most widely used antibiotics for UTIs, and for good reason - it directly stops bacteria from making the proteins they need to survive, clearing the infection at its source.

Many people notice improvement within 24–48 hours, and with a full course, trimethoprim not only treats symptoms but also prevents the infection from spreading to the kidneys. It’s often prescribed as an alternative when nitrofurantoin isn’t suitable.

Directions

  • Take as prescribed by your clinician - usually once or twice daily.
  • Swallow with water, with or without food.
  • Always complete the full course, even if symptoms settle quickly.
  • Drink plenty of fluids to support recovery.

Side Effects

Most people tolerate trimethoprim well. Side effects are usually mild and temporary.

Common (may affect up to 1 in 10 people):

  • Nausea or mild stomach upset
  • Headache
  • Skin rash


Less common (may affect up to 1 in 100 people):

  • Diarrhoea
  • Tiredness
  • Changes in taste


Rare but serious (seek urgent medical advice):

  • Severe allergic reaction (swelling, difficulty breathing, rash)
  • Unexplained bruising or bleeding (possible blood disorder)
  • Yellowing of the skin/eyes (liver issues)


Disclaimer: This is not a complete list of side effects. Always read the patient information leaflet for full details. If you notice anything unusual or concerning, stop taking the medicine and seek medical advice promptly. In an emergency, call 999 or go to A&E.

Warnings

Trimethoprim is widely prescribed for urinary tract infections, but it may not be suitable for everyone. Always tell your prescriber about your full medical history and any medicines you are taking before starting treatment.

  • Pregnancy - Trimethoprim is not usually recommended during pregnancy, especially in the first trimester, as it may affect folic acid levels. Your prescriber will advise on safer alternatives if needed.
  • Blood disorders - This medicine can occasionally affect blood cells. Let your prescriber know if you have a history of anaemia, folate deficiency, or other blood-related conditions.
  • Kidney or liver problems - Trimethoprim may not be suitable for people with significant kidney or liver disease. Dose adjustments may be needed.
  • Other medicines - Trimethoprim can interact with several medicines, including warfarin (increasing bleeding risk), methotrexate, and certain diuretics. Always disclose your full medication list during your consultation.
  • Allergies - Do not take trimethoprim if you are allergic to it or to other similar antibiotics.
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