Trimethoprim is an antibiotic that can be used to treat urinary tract infections caused by bacteria. It is sometimes prescribed to treat chest infections.

Trimethoprim used to be the first choice treatment for UTIs, but guidelines from the National Institute of Health and Care Excellence changed as the bacteria that causes cystitis became resistant to Trimethoprim. Trimethoprim is available in tablet and liquid form.

What are trimethoprim tablets for?

Trimethoprim tablets are used to treat:

• urinary tract infections
• respiratory tract infections

What type of antibiotic is trimethoprim?

Trimethoprim is known as a broad spectrum antibiotic. That means it kills a wide range of bacteria, so can be used to treat different infections.

Trimethoprim works by stopping bacteria from producing folic acid, which they need to survive.

Folic acid helps the production of DNA in the bacteria. Their DNA helps them to grow and increase in numbers, so without the folic acid they are unable to do this. This helps to clear the infection.

How long does trimethoprim take to work?

For most infections, most people feel better within a few days of taking trimethoprim.

How effective is trimethoprim for UTI?

Trimethoprim is no longer the most effective treatment for cystitis. Studies testing the effectiveness of trimethoprim against the bacteria that causes UTIs have shown that 33% of samples tested were resistant against trimethoprim. The current recommended treatment is nitrofurantoin, which was only resisted by 3% of samples.

What dosage is trimethoprim available in?

Trimethoprim is available in two dosages:

• 100mg
• 200mg

The usual dose prescribed for a UTI is 200mg twice a day. The usual dose to prevent other infections is 100mg once a day. The trimethoprim dose you will need will depend on:

• your age
• the infection
• how well your kidneys work.

You should take trimethoprim exactly as your doctor has prescribed. In most adults your doctor will usually prescribe 200mg to be taken twice daily.

For long term treatment or to prevent recurring infections, you may be prescribed 100mg at night. When taking trimethoprim, you should:

• swallow the tablets whole with a glass of water, without chewing.
• take them at the same time each day.

Elderly people who need trimethoprim to treat a UTI and who have kidney problems will usually be given a lower dose.

Trimethoprim is an antibiotic used to treat bacterial infections. Trimethoprim is a prescription only medication, so you cannot get it over the counter.

Can I buy trimethoprim online?

Yes, you can buy trimethoprim online, but it is not something Superdrug Online Doctor advises.

Before you buy any medication online, you should make sure that the place you are buying from is registered with the General Pharmaceutical Council (GPhC). If they are not, then do not buy anything from them as they may be operating illegally.

Superdrug Online Doctor no longer offers trimethoprim, but we can offer alternative treatments.

Can I buy trimethoprim over the counter?

No, trimethoprim is a prescription only medication which means you must have a prescription from a registered doctor before you can get it from a pharmacy.

Trimethoprim can cause side effects but not everyone will experience them. A very common side effect is to have high blood potassium levels.

Common side effects include:

• diarrhoea
• headaches
• hives
• nausea
• skin rashes
• thrush
• vomiting

Rare or very rare side effects include:

• abnormal behaviour
• confusion
• constipation
• convulsions
• cough
• dizziness
• eye redness and pain
• feeling agitated
• hallucinations
• increased sensitivity of skin to the sun
• involuntary movements
• joint and muscle ache
• kidney problems
• pins and needles
• ringing in the ears (tinnitus)
• severe watery/bloody diarrhoea
• sore throat
• sore tongue and mouth
• tiredness
• tremors or shakiness
• vertigo

Other side effects include:

• itching
• high blood creatinine levels and blood urea nitrogen levels

You should stop taking trimethoprim immediately and seek urgent medical attention is you have:

• breathing difficulties
• swelling of the face, lips, tongue, and throat
• chest pain
• shock, fainting or collapse
• blistering/peeling of the skin
• skin lesions
• swelling of the skin
• jaundice
• pancreatitis

How long do side effects of trimethoprim last?

It is unlikely that you will get side effects when taking trimethoprim. Some people have itchy skin when taking it, but this usually goes away when they stop taking trimethoprim.

What should I do if I get side effects?

If you have side effects, speak to your doctor for advice. They may be able to offer a different medication. If you have any serious side effects, you should call 999 or go to A&E straight away. These may include:

• headaches
• fever
• tiredness
• sensitivity to light
• feeling generally ill

You should not take trimethoprim if you:

• are allergic to trimethoprim or any other ingredients included in the medication
• are pregnant
• have severe liver problems
• have any blood disorders such as a particular type of anaemia

Can you take trimethoprim when pregnant?

Trimethoprim is not recommended during pregnancy, especially during the first trimester. That’s because trimethoprim can cause folate deficiency, a nutrient that’s essential for the developing foetus and prevents neural tube defects.

But, it is important to treat UTIs when pregnant. So if you are pregnant, think you might be, or are trying for a baby and require antibiotic treatment, you should tell your doctor.

Can you take trimethoprim while breastfeeding?

Yes, it is thought to be safe to take trimethoprim while breastfeeding because only a tiny amount of the drug passes to the baby in breast milk. If you are worried about the effect of trimethoprim and you are breastfeeding, you should speak to your doctor.

List of medications that can interact with trimethoprim

Trimethoprim does not mix well with several drugs including:

• diuretics (water tablets) and other high blood pressure drugs
• rifampicin (a type of antibiotic)
• blood thinners such as warfarin
• digoxin (used to treat heart problems)
• some anticonvulsants such as phenytoin (epilepsy medication)
• repaglinide and pioglitazone (to treat diabetes)
• bone marrow depressants
• some malaria tablets

You should tell your doctors if you are taking any medication as it may interact with trimethoprim.

Can you drink alcohol when taking trimethoprim?

Yes, you can drink alcohol when taking trimethoprim.

Can you take paracetamol with trimethoprim?

Yes, it is safe to take paracetamol and ibuprofen when taking trimethoprim.

Does trimethoprim affect the contraceptive pill?

Trimethoprim does not affect how the contraceptive pill works. That means you can continue to take the combined pill, mini pill, or emergency contraceptive pill (if needed) and still be protected from pregnancy, if they are taken correctly.

If trimethoprim makes you sick or causes you to have diarrhoea, then your contraceptive pill may not protect you from pregnancy.

If you are concerned, you should read the patient information leaflet that comes with your pill.

In most cases, if you are sick or have diarrhoea within 2 hours of taking the pill, then it is unlikely it will have been absorbed by your body. If you are sick or have diarrhoea, you must ask your doctor for advice.