Trimethoprim

Trimethoprim is an antibiotic – a type of medicine that kills bacteria. It’s a broad-spectrum antibiotic, which means that it can kill a range of different bacteria.

The UTI antibiotic trimethoprim is used to treat cystitis. While cystitis means inflammation of the bladder and can be caused by many different things, the term is usually used as another way to describe a urinary tract infection that affects the bladder.

Cystitis is caused by bacteria, and typically, it causes symptoms including:

• a stinging or burning feeling when you pee
• feeling like you need to pee more often and more urgently
• darker, cloudier, or stronger-smelling pee than usual
• pain in your lower tummy
• blood in your urine

If you have symptoms of cystitis and they do not improve with time or with UTI home remedies, you may need treatment with an antibiotic to clear the infection.

Trimethoprim used to be the preferred treatment for cystitis. However, in recent years there has been an increase in antibiotic resistance to trimethoprim. Antibiotic resistance is when bacteria have evolved so they are not destroyed by medicines which used to be effective against them.

To treat cystitis, nitrofurantoin is now usually recommended as the first-line treatment. However if you are unable to take it or it does not work for you, trimethoprim may be a suitable alternative. Your doctor will advise if trimethoprim is suitable for you.

Trimethoprim is sometimes used to prevent cystitis from recurring (coming back). It’s also sometimes used to treat other conditions, including acne and chest infections.

Trimethoprim has been used to treat UTIs for decades and is a highly effective antibiotic. While nitrofurantoin is now the first-line antibiotic for UTIs, doctors may still prescribe trimethoprim if you are allergic to nitrofurantoin, or if there’s another medical reason it’s not suitable for you.

You need to take trimethoprim tablets orally. It is easiest to take your trimethoprim dose with a glass of water.

To treat cystitis, 1 trimethoprim tablet is normally taken twice a day, for 3 days.

Men and pregnant women usually take a course of trimethoprim for 7 days. Also for pregnant women, this will depend on which trimester you are in so consult your doctor prior to taking trimethoprim. For more severe UTIs, the course can be longer (up to 14 days).

You should take trimethoprim for as long as you have been prescribed it. Your doctor may recommend that for your first dose, you take 2 tablets of trimethoprim. You should always take your full course of trimethoprim antibiotics. Even if you feel better, you should keep taking it until the course is complete – this reduces the chances of the infection coming back.

If you forget a trimethoprim dose, do not take a double dose to make up for it. Continue taking your next dose as normal.

Trimethoprim is sometimes taken to prevent cystitis. The usual dose of trimethoprim to prevent cystitis is 100mg once a day, at night.

If your doctor decides that trimethoprim is the best course of treatment for you, they will give you a dosage schedule to follow.

Here is an outline of doses of trimethoprim for UTI treatment depending on whether you’re taking them as a standard or preventative course. Note that Trimethoprim is not available to request for prescription from ZAVA:

You need a prescription to buy trimethoprim. Once a doctor has prescribed it to you, you can pick it up at a pharmacy.

Trimethoprim is not available to request with ZAVA, however nitrofurantoin which is a more commonly prescribed treatment which works in a similar way is available to order with us online.

To request nitrofurantoin you will need to fill in a short questionnaire that one of our doctors will review. If the doctor thinks nitrofurantoin is a suitable antibiotic for you, they will prescribe it. Your UTI medication then gets delivered to you as quickly as the next day.

You should speak to your doctor before taking trimethoprim if you:

• have kidney disease
• are having dialysis
• have a folic acid deficiency
• are breastfeeding

You should not take trimethoprim if you have:

• an allergy to trimethoprim or any of its other ingredients
• a blood disorder, such as porphyria
• severe liver disease

It’s generally seen as safe to take trimethoprim while trying to get pregnant and in pregnancy, but only after the first 12 weeks. This is because it can affect the levels of folic acid in your body (folic acid plays an important role in the early stages of your baby’s development). If you need trimethoprim while you're trying to get pregnant, or during the first 12 weeks of pregnancy, your doctor will likely recommend taking 5mg of folic acid per day.

If your doctor or health visitor says your baby is healthy, you can take trimethoprim while breastfeeding. Talk to your doctor or midwife if your baby is:

• not feeding as usual
• has a stomach upset
• has oral thrush (a fungal infection in the mouth)

Trimethoprim works by killing bacteria, and it does this by stopping them from producing a substance called folic acid. Bacteria use folic acid to make proteins. Without folic acid, the bacteria cannot survive.

Trimethoprim kills the bacteria that cause cystitis. If you take trimethoprim to treat cystitis, your symptoms should get better straight away and clear up completely after a few days. If they do not, you need to see a doctor for advice on what to do next.

Trimethoprim may cause side effects. These are usually mild, and not everyone will have side effects when taking this antibiotic.

Common or very common trimethoprim side effects include:

• nausea (feeling sick)
• vomiting (being sick)
• diarrhoea
• electrolyte imbalance
• skin rashes and urticaria (hives)
• headache
• fungal overgrowth

If you’re taking trimethoprim long-term, such as for preventing cystitis, there’s a chance it can cause high levels of potassium in the blood, which can cause an abnormal heart rhythm. You may be at greater risk of developing a high level of potassium in the blood if you have kidney problems, diabetes that is not well controlled, or are taking potassium supplements or certain medications. You should speak to your doctor if this applies to you.

If you develop any of the following symptoms, you should stop taking trimethoprim straight away. Call 999 or go to your nearest A&E department if you have:

• signs of meningitis (a very rare side effect), such as headaches, fever, a stiff neck, tiredness, feeling ill, or your eyes becoming very sensitive to bright light
• signs of high potassium in your blood, such as muscle weakness, an abnormal heartbeat, or chest pains
• signs of an allergic reaction, such as difficulty breathing, swelling in your face, lips, tongue or throat
• chest pain, shock, fainting, or if you collapse
• blistering or peeling of the skin, lesions or eruptions in the skin, swelling of the skin (angioedema)
• signs of pancreatitis, such as a sudden, severe upper abdominal pain

Call a doctor or 111 straight away if you experience:

• diarrhoea that lasts longer than 4 days, or contains blood or mucus
• unexplained bruising or bleeding, sore throat, mouth ulcers, fever, or you feel generally unwell – this could be a sign of a problem with your blood

If you are worried about any side effects whilst taking trimethoprim, you can speak to your doctor or pharmacist. You can also report any side effects through the MHRA’s (Medicines & Healthcare products Regulatory Agency) Yellow Card scheme.

Before you buy trimethoprim, you should let your doctor know about any other medicines you are taking. When taken together, the effectiveness of trimethoprim and certain other medicines can change.

Trimethoprim may interact with:

• antibiotics, including rifampicin
• warfarin and heparin (to prevent and treat blood clots) and other anticoagulants (blood thinners)
• some medicines taken after a transplant to prevent or treat rejection, including ciclosporin and azathioprine
• digoxin, taken to treat some heart conditions
• phenytoin (for epilepsy)
• some medicines for malaria including pyrimethamine and dapsone
• some medicines used to suppress the immune system in cancer treatment (for example methotrexate)
• bone marrow depressants
• potassium supplements
• some medicines used to treat high blood pressure and heart conditions (including digoxin, ACE inhibitors, and angiotensin II antagonists)
• procainamide for abnormal heart rhythm
• repaglinide (for diabetes)
• diuretics including eplerenone, spironolactone, amiloride, and triamterene

The medicine usually recommended to treat cystitis is nitrofurantoin. This works slightly differently from trimethoprim but still works to kill the bacteria causing cystitis and is available to request from ZAVA.

Trimethoprim vs nitrofurantoin for UTIs

Trimethoprim and nitrofurantoin are both effective treatments for UTIs. Various medical reviews have shown they have similar success rates when used to treat or prevent UTIs. For example, one study found that:

• nitrofurantoin cured 81.5% of people’s UTIs
• trimethoprim cured 78.4%

However, growing antibiotic resistance to trimethoprim means nitrofurantoin is now usually the first-line treatment for UTIs.

Yes, trimethoprim is usually effective at treating cystitis even though it’s not the first choice offered. Because some bacteria have developed resistance to trimethoprim this does not mean it doesn’t work, just that it’s now used less to stop bacterial resistance from increasing.

Where resistance to trimethoprim has developed, an alternative treatment should be used instead. Nitrofurantoin is usually recommended as the first-line treatment for cystitis, and if it’s not suitable for you, trimethoprim would be an alternative.