Trimethoprim 50 mg / 5 ml suspension – patient leaflet, side effects, dosage

1. What Trimethoprim is and what it is used for

Trimethoprim is an antibiotic which is used to treat or prevent bacterial infections, including urinary tract infections, in adults and children.

2. What you need to know before you take Trimethoprim

Do not take Trimethoprim:

• If you are allergic to trimethoprim or any of the ingredients of this medicine (listed in Section 6).
• If you are pregnant (first 3 months) or might be pregnant, or if you are breast-feeding long-term.
• If you have anaemia or other serious blood disorders.
• If you have severe liver problems.

Warnings and precautions

Talk to your doctor before taking Trimethoprim:

• If you have folate deficiency anaemia (especially in the elderly).
• If you have or might have had acute Porphyria (blood disorders).
• If you suffer from kidney problems or are having dialysis treatment.
• If you are also taking repaglinide (medicine for treating diabetes).
• If you have fructose intolerance or an intolerance to some sugars.
• If you have ever developed a severe skin rash or skin peeling, blistering and/or mouth sores after taking trimethoprim.

Trimethoprim can increase potassium blood levels. Patients at risk of increased potassium blood levels include those with kidney problems, poorly controlled diabetes, or those on certain medicines or potassium supplements. The symptoms of severe hyperkalaemia might include muscle cramps, irregular heart rhythm, diarrhoea, nausea, dizziness or headache. Your doctor may perform blood tests to monitor your potassium blood levels.

Your doctor may wish to do regular blood tests if you need long-term treatments or are prone to anaemia.

Serious skin reactions, such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), drug reaction with eosinophilia and systemic symptoms (DRESS) have been reported in association with trimethoprim treatment. Stop using trimethoprim and seek medical attention immediately if you notice any of the symptoms related to these serious skin reactions described in section 4.

Other medicines and Trimethoprim

Tell your doctor or pharmacist if you are taking, have recently taken or might take any other medicines. In particular:

• Folate antagonists, used to treat folate deficiency (e.g. aminopterin or methotrexate)
• Bone Marrow depressants (e.g. azathioprine, cytarabine, or daunorubicin)
• Repaglinide, used to treat diabetes
• Procainamide, to treat abnormal heart rhythm
• Digoxin, to treat heart conditions
• Diuretics (e.g. water tablets such as eplerenone, spironolactone, amiloride or triamterene)
• Rifampicin, used to treat TB
• Anticoagulants (to prevent clots from forming in the blood e.g. warfarin)
• Phenytoin to treat epilepsy
• Pyrimethamine and dapsone, used to treat malaria
• Immunosuppressant drugs – used in cancer treatment (e.g. methotrexate) or to treat organ rejection after transplant (e.g. azathioprine or ciclosporin).
• Potassium supplements
• Medicines known as ACE inhibitors and angiotensin II antagonists (used to treat high blood pressure and certain heart conditions).
• Heparin (used to treat and prevent blood clots)

Trimethoprim with food and drink:

Trimethoprim can be taken with or without food.

Pregnancy and breast-feeding

If you are pregnant or breast-feeding, think you may be pregnant or are planning to have a baby, ask your doctor or pharmacist for advice before taking this medicine.

This medicine should not be taken during first three months of pregnancy. Treatment with trimethoprim in the first three months of pregnancy may increase the risk of miscarriage. Children born to mothers treated with trimethoprim during the first trimester of pregnancy may have an increased risk of birth defects, in particular neural tube defects (where the spine and spinal cord do not form properly), oral clefts (where the lip and palate do not form properly) and defects affecting the heart.

Ask your doctor or pharmacist for advice if you are pregnant or planning on becoming pregnant or are breast-feeding long term.

Trimethoprim contains sorbitol (E420), methylhydroxybenzoate (E218) and propylhydroxybenzoate (E216)

• Sorbitol (E420): If you have been told by your doctor that you have an intolerance to some sugars, contact your doctor before taking this medicinal product.
• Methylhydroxybenzoate (E218) and propylhydroxybenzoate (E216): may cause allergic reactions (possibly delayed).

3. How to take Trimethoprim

Always take Trimethoprim exactly as your doctor has told you. Check with your doctor or pharmacist if you are not sure. Shake well before use. The recommended dose is:

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The adult dose may need to be reduced depending on how well your kidneys function. Your doctor will advise you.

Renal Impairment

It may be necessary to reduce the dosage if you are suffering from kidney problems. Your doctor will advise you.

If you forget to take Trimethoprim

Take the missed dose as soon as you remember, unless its nearly time for your next dose. Do not take a double dose to make up for the missed dose.

If you take more Trimethoprim than you should

If you take too much Trimethoprim, go immediately to your nearest hospital casualty department, taking your medicine bottle with you to show what you have taken.

If you stop taking Trimethoprim

Remember to keep taking this medicine until your doctor tells you to stop. Do not stop just because you feel better. If you stop too early, your infection may return, or get worse.

If you have any further questions on the use of Trimethoprim, ask your doctor or pharmacist.

4. Possible side effects

Like all medicines, this medicine can cause side effects, although not everybody gets them.

Contact your doctor or hospital at once if you get an allergic reaction such as swelling of the face, lips, tongue or throat, difficulty breathing, shock or collapse. Aseptic meningitis can occur in some patients. This may show as a combination of symptoms such as headache, fever, stiff neck, tiredness, feeling ill and your eyes become very sensitive to bright light.

Stop using Trimethoprim and seek medical attention immediately if you notice any of the following symptoms:

• Reddish patches on the trunk, often with central blisters, skin peeling, ulcers of mouth, throat, nose, genitals and eyes. These serious skin rashes can be preceded by fever and flu-like symptoms (Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN)).
• Widespread rash, high body temperature and enlarged lymph nodes (DRESS syndrome or drug hypersensitivity syndrome).

Tell your doctor or pharmacist if you notice any of the following side effects:

Common (may affect up to 1 in 10 people)

• Feeling and being sick, diarrhoea • Headache
• High levels of potassium in the blood (may result in abnormal heart rhythm) • Skin rashes
• Sore throats or mouth ulcers (due to a decrease in white blood cells) • Thrush.

Very rare (may affect up to 1 in 10,000 people)

• Constipation, severe watery/bloody diarrhoea • Cough
• Agitation • Jaundice (yellowing of the skin or whites of the eyes)
• Abnormal behaviour • Dizziness, tiredness
• Kidney problems (signs may include painful urination or blood in the urine) • Involuntary movements
• Convulsions • Ringing in the ears, vertigo
• Pins and needles, shakiness • Increased sensitivity of the skin to the sun
• Eye redness and pain • Low blood sugar
• Low levels of sodium in the blood (may cause nausea, tiredness, muscle cramping) • Depression, anxiety, sleeping difficulties, nightmares
• Weight loss • Confusion, hallucinations
• Elevation of serum transaminases (an indication of liver damage) • Joint and muscle ache
• Elevation of bilirubin levels • Wheezing, nosebleeds
• Meningitis (signs may include stiff neck, fever and vomiting) • Lupus erythematosus (an auto-immune disorder).

Not known (frequency cannot be estimated from the available data)

• Anaemia (may cause you to feel tired and look pale)
• Elevated levels of methaemoglobin (may cause shortness of breath, tiredness, headache and dizziness)
• Sore tongue and mouth
• Gastro-intestinal disturbance
• Itching.

Reporting of side effects

If you get any side effects, talk to your doctor. This includes any possible side effects not listed in this leaflet. You can also report side effects directly via the Yellow Card Scheme at www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in Google play or Apple App store. By reporting side effects you can help provide more information on the safety of this medicine.

5. How to store Trimethoprim

Keep this medicine out of the sight and reach of children. Store in the original container. Do not use this medicine after the expiry date which is stated on the label or carton. Do not throw away any medicines via wastewater or household waste. Ask your pharmacist how to throw away medicines you no longer use. These measures will help protect the environment.

6. Contents of the pack and other information

What Trimethoprim contains:

• the active substance is trimethoprim; each 5 ml of the oral suspension contains trimethoprim 50 mg.
• the other ingredients are agar, polysorbate 80, saccharin sodium, sorbitol (E420), methylhydroxybenzoate (E218), propylhydroxybenzoate (E216) and purified water (see end of Section 2).

What Trimethoprim looks like and contents of the pack

Trimethoprim is a white, opalescent, viscous oral suspension. This medicine contains no flavour. It is available in 100 ml amber glass bottles with pilfer-proof screw cap and expanded polyethylene liner.

Marketing Authorisation Holder and Manufacturer

Pinewood Laboratories Ltd., Ballymacarbry, Clonmel, Co. Tipperary, Ireland

PL04917/0065

This leaflet was last updated in 01/2026

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