Trimethoprim

Trimethoprim is a prescription-only antibiotic commonly used to treat uncomplicated urinary tract infections (UTIs) in women. UTIs are caused by bacteria — most commonly E. coli — infecting the bladder and urinary tract, causing symptoms such as a burning sensation when urinating, needing to urinate more frequently, cloudy or strong-smelling urine, and discomfort in the lower abdomen. Trimethoprim works by blocking an enzyme that bacteria need to produce folic acid — without it, the bacteria cannot grow or reproduce, allowing your immune system to clear the infection. It is one of the most commonly prescribed antibiotics for UTIs in the UK and can be prescribed quickly and conveniently through Access Doctor following a short online consultation.

Most women begin to feel a significant improvement in their UTI symptoms within 24 to 48 hours of starting trimethoprim. However, it is very important to complete the full course of antibiotics even if you feel better sooner — stopping early can allow the infection to return and may contribute to antibiotic resistance. If your symptoms have not improved within 48 hours of starting treatment, or if they get worse at any point, speak to your GP as you may need a different antibiotic.

The usual dose for treating a UTI in adults is one 200mg tablet taken twice a day — once in the morning and once in the evening, roughly 12 hours apart. Take each tablet with a full glass of water, and you can take it with or without food — taking it with food can help to reduce any stomach upset. Swallow the tablets whole and do not crush or chew them. The standard course length for an uncomplicated UTI is 3 to 7 days — Always complete the full course.

Most women tolerate trimethoprim well and complete their course without any significant problems. The most commonly reported side effects are nausea, an upset stomach, itching, and a mild skin rash. Some women may develop a thrush infection during or after treatment, which can be treated separately with an antifungal cream or tablet. In rare cases, more serious side effects can occur — including a severe skin rash, significant swelling of the face or throat, or unusual bruising or bleeding. If you experience any of these, stop taking trimethoprim immediately and seek urgent medical attention. If you develop severe or bloody diarrhoea during or after treatment, contact your GP as this can occasionally indicate a bowel infection.

Alcohol is not strictly prohibited while taking trimethoprim, but it is sensible to keep it to a minimum during your course of treatment. Drinking alcohol while you have a UTI can irritate the bladder further and worsen symptoms such as frequency and burning. It can also slow your body's recovery from infection. For the best results, try to avoid or significantly reduce alcohol intake until your UTI has fully cleared and your course of antibiotics is complete.

This is a commonly asked question. Current UK guidance confirms that trimethoprim does not reduce the effectiveness of the combined oral contraceptive pill or the mini pill. You do not need to use additional contraception solely because you are taking trimethoprim. However, if you experience significant vomiting or diarrhoea while taking it, your pill may not be absorbed properly during that time — in which case use additional contraception such as condoms until your next period starts.

Trimethoprim should be avoided during the first trimester of pregnancy, as it can interfere with folic acid — which is essential for the healthy development of a baby's neural tube — and may increase the risk of certain birth defects. It is also not recommended in the later stages of pregnancy. If you are pregnant and have a UTI, speak to your GP urgently, as UTIs in pregnancy can become serious quickly and need prompt treatment with a pregnancy-safe antibiotic such as nitrofurantoin or cefalexin. If you are breastfeeding, trimethoprim can pass into breast milk in small amounts — speak to your own GP before taking it who can advise on the safest option for you.

Alongside taking your antibiotic course, there are several self-care steps that can help speed up your recovery and reduce the risk of future UTIs. Drink plenty of water — at least 6 to 8 glasses a day — to help flush bacteria out of your urinary tract. Avoid holding in urine for long periods and always wipe from front to back after using the toilet. After sex, urinating as soon as possible can help to flush any bacteria away before it reaches the bladder. Avoid using perfumed soaps, bubble baths, or intimate deodorants around the genital area, as these can irritate the urethra and make infections more likely.