Trimethoprim

Trimethoprim is a broad spectrum antibiotic. One of its main uses is to treat bacterial urinary tract infections (UTIs). Urine is produced in the kidneys, temporarily held in the bladder and then passed through the urethra (the urine tube). Infection usually starts at the exit of the urethra, which is at the tip of the penis in men, or in the vaginal fold in women and moves into the bladder. If untreated, the infection can travel upwards to the kidneys, where it becomes much more serious. In its use against UTIs, Trimethoprim is targeted at bacterial infections of the bladder (cystitis) before they reach the kidney.

The active ingredient Trimethoprim prevents bacteria from taking up folic acid and therefore interferes with their reproduction. In the same way, it also prevents you absorbing folic acid, which is why Trimethoprim must not be taken during pregnancy. The symptoms should disappear within a few days. However, you must complete the full 3-day course of antibiotics to ensure the infection is completely treated to prevent the infection from recurring.

You should feel better within a day or two of taking Trimethoprim tablets. One course of Trimethoprim will last three days, after which you should have noticed a significant improvement. If your symptoms persist, it is important for you to seek medical help immediately. Your doctor will carry out further tests to establish the nature of your infection. It is important to seek help without delay, as urinary tract infections can quickly spread to the kidneys, making them more painful and harder to treat. If Trimethoprim does not work, it may be because your UTI is Trimethoprim resistant.

No. Trimethoprim is not targeted at the Chlamydia bacterium, which is a sexually transmitted infection (STI) that also causes Cystitis. If you have a UTI, it does not necessarily mean you have Chlamydia. In fact, Chlamydia is the cause of only a small proportion of UTIs. If you think you have chlamydia, please visit our chlamydia page for further information.

In rare cases, patients are allergic to Trimethoprim or one of the ingredients. If this applies to you, your doctor will be able to advise you, which alternative treatment to take. If you are suffering from a blood disorder or kidney disease, you must also speak to your doctor, as Trimethoprim may be harmful for you.

No. You must not use Trimethoprim if you are pregnant. Trimethoprim can lead to a folic acid deficiency which can, especially in the early stages of pregnancy, lead to an increased risk of neural tube defects. Taking Trimethoprim during this time can seriously affect the formation of your baby’s brain and spine.

Trimethoprim is passed into breast milk, however, short-term use of Trimethoprim is not a problem. You should consult a doctor to discuss the suitability of Trimethoprim while breast-feeding.

Antibiotics can make oral contraceptive pills less effective. In addition, antibiotics may cause vomiting or diarrhoea, which affect your contraceptive protection. Use need to use a condom in addition to your regular oral contraceptive to prevent unwanted pregnancy while taking Trimethoprim.

Yes. There is no interaction between alcohol and trimethoprim. Please note, that it is not advisable to consume alcohol during a bout of cystitis, as it can irritate your bladder further.

• If you are under 12 years old
• If you are pregnant
• If you are allergic to Trimethoprim or any other ingredients of the pill
• If you have severe kidney disease
• If you have a severe liver disease
• If you have a blood disorder

• If you have kidney disease or are having dialysis treatment
• If you have low levels of folic acid
• If you are using other antibiotics, especially rifampicin
• If you are using anticoagulants to prevent your blood clotting (e.g. Warfarin)
• If you are using Ciclosporin e.g. to prevent transplant rejection.
• If you are using digoxin e.g. for heart conditions
• If you are using phenytoin e.g. for epilepsy
• If you are using pyrimethamine e.g. to treat malaria
• If you are using bone marrow depressants