Trimethoprim is an antibiotic medicine indicated for the treatment of bacterial infections, including cystitis. It is available as a generic tablet and an oral suspension solution.

We do not provide cystitis medications via our online clinic service. See your GP if you think you may have cystitis or are experiencing similar symptoms.

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PLEASE NOTE: This treatment is not available through our online pharmacy service. This page is for information only. If you are experiencing any of the symptoms related to the condition(s) this medication treats, we strongly recommend that you see your GP in person.
Product information

Trimethoprim is an antibiotic medicine. It is used in the treatment of various bacterial infections, including cystitis. Presently, this antibiotic is the first-line treatment for UTIs. Trimethoprim is sold as a generic tablet and oral suspension fluid, but the same medication has previously been made by GlaxoSmithKline under the names Proloprim and Triprim.

It is thought that most will women will encounter cystitis at some point in their lives. The condition can be brought on by the presence of certain bacteria in the urinary tract, and can cause inflammation and feelings of pain in the bladder, as well as urinary discomfort. Some may notice that their urine becomes dark or discoloured too.

There are a number of reasons why someone might develop cystitis; but many of them involve the transfer of bacteria from other parts of the body, or from foreign objects, to the vagina. Bathroom habits (such as wiping from the anus to the vagina) can induce infection, as can sex, or the use of tampons or vaginally-inserted contraceptive devices.

Milder cases of cystitis may clear up without the need for treatment. In some instances, the body’s immune system is able to tackle the infection and stop it from developing. However, persistent or severe incidences of the illness will usually necessitate a course of medication.

When treatment for bacterial infections is required, this is issued in the form of antibiotics.  This is because they eliminate the illness by combating the bacteria responsible. Trimethoprim is the preferred treatment for cystitis, and is available as a standard tablet, as well as an oral suspension treatment.

Trimethoprim and Trimethoprim Oral Suspension work by stopping the growth of the infecting bacteria. This is done by inhibiting their capacity to duplicate themselves through the production of DNA material. Once the bacteria is no longer able to spread, the immune system takes over and destroys what remains of the infection.

This medicine is not available to buy through our clinic service. Talk to your GP if you think you may have cystitis, or are experiencing any of the symptoms referred to above.

Active Ingredient

The functioning constituent in both versions of this medicine is Trimethoprim. This is a bacteriostatic antibiotic, which means that it disables the target bacteria’s ability to self-replicate. It has been marketed under various names by GlaxoSmithKline, but the edition available here is a generic medicine. Aspen also sell the medication as a combination with co-trimoxazole, under the name Septrim.

To spread, bacteria need to reproduce, and they do so by copying their own DNA material. To create the right conditions to do this, they need to generate folic acid. Trimethoprim stops the bacteria from multiplying in numbers by preventing them from synthesising this acid. As a result, the bacteria becomes prone to attack from the immune system, which kills off their remaining number.

Page last reviewed:  23/10/2018


It is essential when using any medication to read the instructions provided first. Adhering to the guidelines set out in these, and following the directions supplied by your doctor, will help you to minimise the risk of side effects, and increase the efficiency of the medicine.

  1. Take as directed by your prescriber
  2. For cystitis infections, this might be one 200mg tablet or two 100mg tablets, taken twice a daily for a specified number of days.
  3. Swallow tablets whole with water.
  4. For the Oral Suspension fluid, see the instructions provided or refer to your prescriber’s directions. For adults, this might be 20ml taken twice a day.
  5. Never exceed the prescribed amount.
  6. Do not make up for a missed dose with a double dose. Continue taking the treatment as normal.

These directions are only intended as a guide. Please refer to the patient information leaflet for more detailed instructions.

Download Trimethoprim PDF

Download Trimethoprim Oral Suspension PDF

Page last reviewed:  23/10/2018
Please read the patient information leaflet for this medicine fully before use:

Trimethoprim 200mg

Trimethoprim 200mg

Trimethoprim 50mg/5ml

Side effects & Warnings

Side effects

Even though only a minority of people may experience them, you should always be aware of the potential side effects a medicine may cause. This is so that you can act fast and get the medical help you need if you notice the appearance of anything unusual. Side effects associated with this medicine include:

Common (frequency unknown):

Diarrhoea, nausea and vomiting, headache, rash, anaemia, thrush, sore throat, mouth ulcers.

Very rare (1 in 10000 people or less):

Feelings of agitation, allergic reactions, cough, redness of the eyes, low blood sugar, photosensitivity, kidney problems, constipation, jaundice, dizziness, tiredness, convulsions, sore tongue.

Contact your doctor if you notice any of the above. This is not a complete list of side effects. For a more detailed account, refer to the leaflet provided with the product.

Taking it with other medicines

Antibiotics can react with other medicines and affect their efficacy. Inform your prescriber during consultation of any other medications you are using. Never use more than one product or medication for cystitis unless your doctor tells you to.

If you are taking any of the following treatments, you may be unable to use Trimethoprim, or only be able to use it under careful medical supervision: repaglinide, procainamide, digoxin, diuretics, rifampicin, anticoagulants, phenytoin, pyrimethamine, dapsone, or immunosuppressant drugs.

Conditions to look out for

Disclose your medical history to your prescriber before use. Kidney problems, folic acid deficiency, high potassium levels, or porphyria, are examples of conditions that may affect your suitability to the medicine.

Pregnancy and breastfeeding

Trimethoprim must not be used during pregnancy.

If you are planning on becoming pregnant or are breastfeeding, speak to your doctor before using this drug.

Driving using machinery

Your driving and capacity to use machines is not likely to be affected by this medication.

Lactose intolerance

This medicine contains lactose. Your prescriber needs to know if you have any intolerances to sugar.

Page last reviewed:  23/10/2018
Please read the patient information leaflet for this medicine fully before use:

Trimethoprim 200mg

Trimethoprim 200mg

Trimethoprim 50mg/5ml


Can I still drink alcohol?

Alcohol is not known to affect the performance of this product. However, it can inhibit the function of some antibiotics, so we would recommend that you do not drink alcohol while using this medication.

Will I still be able to drive?

This medication should not have any effect on your capacity to drive. But if you experience any side effects which could impair your judgement or coordination, you should not drive and seek medical advice right away.

Can I take the medicine while pregnant?

No. This product is not suitable for use by those who are pregnant or breastfeeding.

How should I store it?

Always in a dry environment at room temperature, away from direct sunlight.

Am I allergic to anything in the medicine?

The tablets contain trimethoprim, lactose monohydrate, povidone K30, crospovidone, sodium starch glycolate Type A and magnesium stearate.

Trimethoprim Oral Suspension fluid contains trimethoprim, xanthan gum(E415), maltitol
liquid (E965), polysorbate 80, microcrystalline cellulose (E460), saccharin sodium(E954), citric acid monohydrate, sodium carboxymethylcellulose(E466), sodium methyl parahydroxybenzoate(E219), sodium propyl parahydroxybenzoate(E217), aniseed flavour and purified water.

Do not use either of the above if you are allergic to any containing ingredients.

Is it available over-the-counter?

No. You can only buy Trimethoprim with a prescription. This is because a doctor will need to assess the suitability of this medicine before issuing it to you.

Is it right for me?

Make an appointment with your GP if you think you may have cystitis. They will conduct an assessment of your symptoms and issue a prescription for treatment if required.


Page last reviewed:  23/10/2018

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