Trimethoprim

What is trimethoprim?

Trimethoprim is an antibiotic primarily prescribed to treat cystitis. Cystitis is an inflammation of the bladder that is most commonly caused by an infection. For this reason, cystitis is often referred to as a ‘UTI’ (urinary tract infection). In some cases, trimethoprim is prescribed to treat other infections such as chest infections.

How does trimethoprim work?

Trimethoprim is an antibiotic known as a dihydrofolate reductase inhibitor, which is used to treat bacterial infection. It works by inhibiting the production of folic acid by bacteria at the site of infection, preventing bacteria from being able to grow and spread.

How long does it take for trimethoprim to work?

Trimethoprim will usually make you feel better within a few days. However, like all antibiotics, it is vital that you complete the full course prescribed to you, even if you feel better to avoid developing a resistant infection. If you’ve finished the course and you’re not feeling any better, it’s important to see your GP as you may need a longer course of trimethoprim or an alternative treatment. 

Other uses of trimethoprim

Trimethoprim is primarily used to treat bacterial infections in the urinary tract. In some cases, it can be used for long-term prevention of recurrent UTIs. It can also be used to treat chest infections and acne.

Active ingredients

The active ingredient in trimethoprim is 200mg trimethoprim.

Inactive ingredients

The inactive ingredients in trimethoprim are colloidal silicon dioxide, lactose, macrogol, magnesium stearate, povidone, sodium starch glycollate, stearic acid and E460. 

Please note: different manufacturers of generic Trimethoprim can use different inactive ingredients in their drugs than those listed above.

Which ingredients can cause an allergic reaction?

In rare cases, it's possible to have a serious allergic reaction to trimethoprim which presents as a rash, trouble breathing, facial/lip swelling, and dizziness. If you experience these after taking the medication please seek medical attention as soon as possible.

How to use trimethoprim?

Always take trimethoprim as instructed by a healthcare professional. Swallow the tablet or tablets at the same times each day with a glass of water. If you take more trimethoprim than you should, contact a doctor immediately. If you forget to take a dose, take it as soon as you remember and then take your next dose at the usual time. Never take a double dose to make up for a missed one.

Trimethoprim dosage

The typical dose of trimethoprim for the treatment of uncomplicated mild cystitis in women is 200 mg twice daily for 3 days. If you are male, have severe symptoms, or have chronic cystitis (recurrent or persistent bladder irritation), your doctor may prescribe a different dose. Always take the dose prescribed for you. 

What if I take too many trimethoprim?

Always take the dose of trimethoprim prescribed by your doctor. If you take too much, contact a doctor immediately. 

When can I stop taking trimethoprim?

Your doctor will tell you when to stop taking trimethoprim. It is vital that you follow instructions and continue to take trimethoprim for the full course prescribed to you. Do not stop taking trimethoprim just because you feel better.

Do I need to finish the course of trimethoprim even if my symptoms have resolved?

You should always finish the course of antibiotics prescribed to you, even if you feel better after a few days. This is vital in preventing bacteria from developing antibiotic resistance.

Trimethoprim side effects

Like all medications, trimethoprim can cause side effects in some people. The most frequent side effects are itchy skin (pruritus), a skin rash (which occurs in up to 7% of patients) and mild, gastrointestinal disturbances including nausea, vomiting and diarrhoea. These effects are generally mild and resolve quickly after stopping the medication. If they are troublesome, speak to your doctor. 

If you experience any of the following rare but severe side effects, stop taking trimethoprim and seek immediate medical attention:

• Swelling of the face, lips, tongue or throat, or difficulty breathing
• Chest pain, shock, fainting or collapse
• Blistering or peeling of the skin, skin eruptions or lesions, or deep swelling of the skin known as angioedema
• Symptoms of pancreatitis (severe upper abdominal pain, often radiating through to the back)
• Jaundice (yellowing of the skin)

The following side effects can affect up to 1 in 10 people:

• High levels of potassium in the blood, which may manifest as palpitations or problems with the heart rhythm
• Nausea, vomiting or diarrhoea
• Headache
• Skin rashes or itchy skin
• Anaemia, which may cause you to appear pale and feel tired
• Sore throat or mouth ulcers
• Thrush

The following side effects are very rare, affecting up to 1 in 10,000 people:

• Constipation
• Severe, watery or bloody diarrhoea
• Cough
• Agitation or abnormal behaviour
• Aseptic meningitis, with symptoms such as headache, fever, stiff neck, tiredness, feeling unwell and sensitivity to bright lights
• Kidney problems, painful urination or blood in the urine
• Dizziness, tiredness
• Convulsions or involuntary movements
• Pins and needles, shakiness or tremors
• Ringing in the ears, vertigo
• Eye redness or pain
• Sensitivity to sunlight
• Low blood sugar levels, low levels of sodium in the blood, which may cause nausea, tiredness or muscle cramps
• Anorexia
• Depression, anxiety, sleeping difficulties, nightmares, confusion, hallucinations
• Jaundice (yellowing of the skin and whites of the eyes), elevation of serum transaminases (an indication of liver damage), or elevation of bilirubin levels
• Joint and muscle ache
• Shortness of breath, wheezing, nosebleeds
• Meningitis (stiff neck, fever, vomiting)
• Lupus erythematosus
• Purple discolouration of the skin
• Fever
• Anaemia or reduction in numbers of blood cells

Contraindications

Do NOT take Trimethoprim if you:

• Are allergic to trimethoprim or any of the other ingredients in this medication
• Are pregnant
• Have a blood disorder
• Have severe kidney disease
• Have severe liver disease

Before taking Trimethoprim, speak to your doctor if you:

• Have kidney disease or are having dialysis treatment
• Have a deficiency of folic acid
• Are elderly
• Are taking any other medications
• Are anaemic
• Have poorly controlled diabetes
• Have an abnormal heart rhythm

Drug interactions

Before taking trimethoprim, tell your doctor or pharmacist if you are taking any other medications, including those purchased over the counter without a prescription. In particular, tell your doctor or pharmacist if you are taking or have recently taken any of the following:

• Antibiotics such as rifampicin
• Anticoagulants such as warfarin
• Digoxin for a heart condition
• Phenytoin for epilepsy
• Pyrimethamine or dapsone for malaria
• Immunosuppressant drugs used in cancer treatment (such as methotrexate) or to treat organ rejection following a transplant (such as azathioprine or ciclosporin)
• Bone marrow depressants
• Spironolactone for fluid build-up
• Repaglinide for diabetes
• Diuretics, such as water tablets furosemide or eplerenone
• Procainamide for abnormal heart rhythm

How to cope with trimethoprim side effects?

Trimethoprim does not usually cause side effects, but when it does, they tend to be mild and easy to manage. Mild rashes and itching can be treated by taking antihistamines, which can be purchased over the counter from a pharmacy. If you experience nausea when you take your tablets, try taking them with or after a meal, and avoid rich or spicy foods. This is particularly important if your nausea leads to sickness, as Trimethoprim may not be absorbed by the body. Mild diarrhoea can be treated by staying hydrated and drinking plenty of water, but you should not take other medicines to treat diarrhoea without consulting a pharmacist. Headaches resulting from dehydration can be managed by staying hydrated, and by taking over-the-counter painkillers such as paracetamol and ibuprofen if needed.

Trimethoprim and alcohol

There is no known interaction between trimethoprim and alcohol, however, alcohol is best avoided if you have cystitis as it can also irritate your bladder, exacerbating your symptoms.

Trimethoprim and pregnancy

Trimethoprim should not be used during pregnancy.

Trimethoprim and breastfeeding

If you are breastfeeding, speak to a doctor for advice before taking this medication.

How to avoid UTIs?

Urinary tract infection (UTI) is the most common cause of cystitis, particularly in women. UTIs are caused by bacteria, usually E. coli from the bowel, entering the urethra and travelling up the urinary tract. UTIs often clear up on their own but do have a tendency to recur. There are some simple measures you can take to help prevent UTIs in the future. Avoid using perfumed soaps or bubble baths when cleaning your genitals, and avoid using heavily perfumed washing detergents for your underwear. Condoms and contraceptive diaphragms with spermicidal lubricant on them can also disturb the bacterial imbalance in the vagina, so try and avoid these. Go to the toilet as soon as you feel the urge to pee, and empty your bladder as soon as possible after having sex. Always wipe from front to back when you go to the toilet to avoid the spread of bacteria to the urethra. Avoid wearing tight jeans and trousers, and choose cotton underwear over synthetic materials such as nylon. Drinking plenty of water and staying well hydrated helps to flush out any bacteria in the urethra and prevent infection. 

Trimethoprim vs nitrofurantoin

Nitrofurantoin is another antibiotic that is also commonly prescribed for the treatment of cystitis and urinary tract infection. Both trimethoprim and nitrofurantoin are effective treatments for UTI, but each may be more suited to different patients. For example, trimethoprim is not suitable for pregnant women, or those taking certain other medications. Nitrofurantoin is also less suitable for those with kidney disease. Nitrofurantoin might also be used if you’ve previously been treated with trimethoprim. Speak to your doctor for advice on which antibiotic would be most suitable for you.

Alternatives to trimethoprim

There are a range of antibiotics used in the treatment of UTIs. The right choice of antibiotic will depend on your medical history, the severity of your infection, and if you have been treated for a UTI before. Other antibiotics often used for UTIs include nitrofurantoin, cefalexin, amoxicillin, ciprofloxacin and co-amoxiclav. Your doctor will be able to advise which is most suitable for you.

Is Trimethoprim an antibiotic?

Yes, trimethoprim is an antibiotic used to treat bacterial infection.

Will trimethoprim stop my contraceptive from working?

Trimethoprim does not interact with any contraceptives, however, it’s advisable to avoid sexual intercourse until your infection has cleared up.
 

Will trimethoprim give me thrush?

Thrush (vulvovaginal candidiasis) can occur in people taking trimethoprim. If you experience symptoms of thrush (typically a white lumpy vaginal discharge associated with vulval itching or discomfort) you should see your GP for treatment. Thrush is easily treated with oral or intravaginal antifungal medications.