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Please note that the first line treatment for cystitis that is caused by a bacterial UTI is Nitrofurantoin, as there is quite a high bacterial resistance to Trimethoprim. Therefore it is wise to only use Trimethoprim to treat a UTI after a urine test has confirmed that the bacterial strain causing the infection is sensitive to Trimethoprim. Please note that this treatment is currently only offered for female patients. If you are male and are experiencing symptoms of a urinary tract infection, you should visit your GP or a sexual health clinic as this could be a sign of another infection or a more serious underlying problem.


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What is Trimethoprim?

Trimethoprim is an antibiotic medication commonly used for bladder infections and urinary tract infections (UTIs) – the most common being cystitis. It treats the infection while reducing uncomfortable symptoms quickly.

Whilst Trimethoprim is occasionally prescribed to treat other kinds of infections such as acne or chest infections, it is sold at euroClinix only for the treatment of UTIs.

The active ingredient trimethoprim can also be found in combination therapies with other antibiotics. For instance, Co-trimoxazole contains a combination of trimethoprim-sulfamethoxazole to treat a whole host of bacterial infections including pneumonia, bronchitis, UTIs, ear infections (otitis media) and gastrointestinal infections.

A reduced dose of Trimethoprim is commonly prescribed by pediatrics for UTIs in children (18 years and below), but at euroClinix we only provide treatment to adults. It’s recommended that you accompany your child (if applicable) to a pediatrician or GP if you think they have a UTI.

We offer Trimethoprim in 100mg and 200mg doses:

You can also be prescribed Trimethoprim in the form of an oral solution, known as Primsol, but only the tablets are offered at euroClinix.

All you have to do is fill out a short and discreet consultation form and one of our registered doctors will decide which dose is suitable for you.

How does Trimethoprim work?

Trimethoprim is an antimicrobial (antibacterial) that belongs to a class of drugs known as folate antagonists or antifolates. It works by preventing the bacteria that causes the infection from producing folate, which is what it needs to survive and multiply. The antibiotic does this by inhibiting the secretion of the DHFR (dihydrofolate reductase) enzyme, an enzyme that is key in folate growth. As a result of this inhibition, the bacteria cannot spread, which allows the immune system to destroy the infection.

Trimethoprim was designed, specifically, to tackle gram-negative bacteria (GNB) such as the Escherichia coli (E.Coli) bacteria that causes cystitis. GNB is a strain of bacteria that has thick outer cell walls which makes them harder to kill, as opposed to gram-positive bacteria (GNP) like staphylococcus that do not have a cell wall, making them more absorbent. GNP are less likely to be pathogenic (cause illness) as many types of the bacilli live harmlessly on the body, where they are known as resident flora. Both strains of bacteria are becoming more and more resistant to antibiotic treatments so it’s important you take Trimethoprim as instructed by your doctor.

Who can take Trimethoprim?

Trimethoprim is a commonly used antibiotic that is widely tolerated by most people. However, you should not take it if you:

Ask a doctor before taking if you:

Trimethoprim can increase potassium blood levels, and therefore can cause complications in those who already have high levels of potassium in their blood. This means those who have poorly controlled diabetes, kidney problems or are on certain potassium supplements are more at risk of hyperkalemia (a condition where your blood-potassium levels are too high).

It is not suitable for pregnant women or women who think they may be pregnant as it has been known to harm the unborn baby. Equally, Trimethoprim can be present in breast milk if taken whilst breastfeeding, which could also harm a newborn.

You should detail all your medical information and any medication you are taking during your consultation, as some antibiotics may react negatively with other medications.

How do I take Trimethoprim?

This medication should be taken as directed by your doctor. Different doses of Trimethoprim require slightly different treatment courses as they treat different ailments.

Trimethoprim 200mg is usually prescribed to treat uncomplicated urinary tract infections. It must be taken twice a day for 3-14 days to effectively clear the infection. Usually a short course of Trimethoprim will completely treat the infection. However, sometimes, a longer-term treatment is needed to avoid a reappearance.

Trimethoprim 100mg is usually prescribed for chronic UTIs in adults for a longer course. In these cases, it must be taken once a day at night.

Trimethoprim tablets should be swallowed whole with a glass of water, and they can be taken with or without food.

It is important to take antibiotics exactly as instructed. Even if your symptoms improve quickly, you should always finish the entire course of medication. Not only could your infection come back if you stop taking them too soon, but bacteria can build up resistance to antibiotics, which will make them less effective at treating infections in the future.

If you miss a dose, take your missed dose when you remember and then your next dose at your usual time. If you realise you missed a dose, and it’s nearly time for your next dose, you should not take two doses on the same day. It’s unlikely that a high-dose of Trimethoprim will harm you, it may just worsen or induce temporary side effects.

You should always read the patient information leaflet thoroughly before beginning any new medication. You can find the patient information leaflet at the bottom of this page.

Trimethoprim and alcohol

While you can drink alcohol while on Trimethoprim, it is not recommended. You should drink plenty of clear liquids and refrain from drinking alcohol if you are using it to treat a urinary tract infection or cystitis. Drinking alcohol whilst taking Trimethoprim could cause nausea, vomiting and other side effects.

Does Trimethoprim react with other medicines?

You should always inform your prescriber if you are taking any other medicines, whether they are over the counter or have been prescribed, because there can be drug interactions. This is also true of Trimethoprim, and you should notify your healthcare provider if you are taking any of the following medications:

If you are not sure whether you take any of these medications, please consult your GP or a healthcare professional.

What are the side effects of Trimethoprim?

As with all medications, it is possible that you may experience side effects, although not everyone will get them.

For those who do get them, the most common side effects (1 in 10) include:

  • Feeling sick
  • Diarrhoea
  • Headache
  • Itching or mild skin rash
  • Thrush
  • Hives

These symptoms are moderate, manageable and will most likely disappear once you finish your course of treatment. You may experience some rarer symptoms (occurring in 1 in 10,000) including a sore throat, tiredness or joint ache. For a more comprehensive list of rare side effects, please refer to the patient information leaflet.

Whilst the incidence is low, you may experience more serious side effects. If you experience any of the following symptoms, you may be having an allergic reaction or more severe complications. In this case, you should discontinue taking Trimethoprim and seek immediate medical attention:

  • Difficulty breathing
  • Swelling of the face, tongue, throat or lips
  • Blistering or peeling of the skin
  • Shock, fainting, or collapse
  • Chest pain
  • Inflammation of the pancreas (pancreatitis)
  • Skin eruptions or lesions
  • Deep swelling of the skin (angioedema)
  • Yellowing of the skin or eyes (jaundice)

If you are not sure about or experience any of these adverse effects, speak to a healthcare professional.

Where can I buy Trimethoprim online?

You can buy Trimethoprim tablets online from euroClinix by completing an online consultation form. Then, one of our UK doctors will review your consultation to ensure that this treatment is suitable for you. If approved, your prescription will be dispatched and dispensed by our pharmacy. Your order will then be sent with free next-day delivery, so you can start to get better sooner.

Note: You must complete a short online consultation so that our doctor can ensure that the treatment is suitable for you. The above pricing should only be used as a reference. The final decision to issue this treatment lies with the prescribing doctor.

Medically reviewed by Dr. Caroline Fontana Written by our editorial team
Last reviewed 27-07-2022
Trimethoprim information
Product nameTrimethoprim
Active ingredient(s)Sulfamethoxazole
ManufacturerCrescent Pharma
Trustpilot rating4.7/5
Trustpilot reviews83
AvailabilityIn stock
DescriptionTrimethoprim is an antibiotic that is used as an effective treatment for the bladder infection cystitis.
ExemptionSubject to medical prescription
Available dosage100mg, 200mg
ApplicationWomen over 18 with the symptoms of cystitis
UsageTake 1 tablet twice a day for up to 14 days
Drug classSulfonamides and folic acid inhibitors
Alcohol consumptionNo influence
When breastfeedingCaution is recommended, ask your doctor
When pregnantCaution is recommended, ask your doctor
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Trimethoprim reviews
Excellent 4.7 83 patients have reviewed Trimethoprim on Trustpilot
23 Jan

Very good antibiotic always treats the symptoms quickly and completely

Customer Mrs Joyce Percival
09 Nov

First prescribed for my chronic cystitis years ago and still reliable today. Complaint managed by 1x100mg every third or fourth day and never any side...

Hazel Whinfrey
21 Mar

Very good product always produces excellent results

Customer Mrs Joyce Percival
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