Trimethoprim is used to treat infections which are caused by bacteria, such as some chest infections and urine infections. It works by killing the bacteria responsible for the infection. is used to treat infections which are caused by bacteria, such as some chest infections and urine infections. It

What is Trimethoprim?

Trimethoprim is used to treat infections which are caused by bacteria, such as some chest infections and urine infections. It works by killing the bacteria responsible for the infection.

A urine infection is often called a urinary tract infection (UTI) by doctors. Most urine infections are caused by bacteria that come from your own bowel. They are usually easily treated with a short course of trimethoprim. Occasionally, longer-term treatment may be needed to prevent infections from coming back.

Before taking Trimethoprim

Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking trimethoprim it is important that your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breast-feeding.
  • If you know you have low amounts of the vitamin folic acid.
  • If you have problems with the way your kidneys work.
  • If you have a blood disorder, or a condition known as porphyria (this is a rare inherited blood disorder).
  • If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • If you have ever had an allergic reaction to a medicine.

How to take Trimethoprim

  • Before you start this treatment, read the manufacturer's printed information leaflet from inside your pack. The leaflet will give you more information about trimethoprim and a full list of side-effects which you may experience from taking it.
  • Take trimethoprim tablets exactly as your doctor tells you to. Your dose will depend upon whether you are being treated because you have an infection, or to prevent an infection. As a guide, the dose for adults with an infection is 200 mg twice daily (morning and evening). The adult dose to prevent an infection is 100 mg at night. If trimethoprim has been prescribed for a child, it is likely that you will be supplied a liquid medicine - the dose will depend upon the age of the child, so read the directions on the label carefully to make sure you give the correct dose.
  • Space your doses out evenly throughout the day - this means that tablets/medicine prescribed twice daily should be taken every 12 hours. You can take trimethoprim before or after meals.
  • Keep taking this antibiotic until the course is finished, unless you are told to stop. A normal course of treatment is likely to last 3-14 days. It is important that you do this even if you feel well, otherwise your infection may come back.
  • If you forget to take a dose, take it as soon as you remember. If it is almost time to take your next dose when you remember, skip the missed dose and take your next dose when it is due. Do not take two doses together to make up for a forgotten dose.

Side effects of Trimethoprim

  • Nausea
  • vomiting
  • gastrointestinal upset
  • dermatological reactions such as pruritus and skin rash

Rare cases of erythema multiforme, Stevens Johnson syndrome and toxic epidermal necrolysis have occurred. Disturbances of liver enzyme values and jaundice have been associated with trimethoprim. Isolated cases of aseptic meningitis, myalgia and uveitis have been reported. Photosensitivity and allergic reactions including angioedema and anaphylaxis have been reported. There is an increased risk of hyperkalaemia, especially in patients with impaired renal function and in elderly patients. Trimethoprim may affect haemopoiesis.

How to store Trimethoprim

  • Keep all medicines out of the reach and sight of children.
  • Store in a cool, dry place, away from direct heat and light.

If you have any more questions please ask your Pharmacist.

Remember to keep all medicines out of reach of children

Please Note: We have made every effort to ensure that the content of this information sheet is correct at time of publish, but remember that information about drugs may change. This sheet does not list all the uses and side-effects associated with this drug. For full details please see the drug information leaflet which comes with your medicine. Your doctor will assess your medical circumstances and draw your attention to any information or side-effects which may be relevant in your particular case.


Health Reference: Urinary tract infection