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Brand Name(s) : Trimopan, Monotrim
Side Effects


Trimethoprim should be used with caution in: patients with renal impairment (kidney disease or having dialysis), patients with folate deficiency, patients with liver problems , the elderly, during breast feeding, and in patients with acute porphyria.

It should not be used in: patients with any blood disorder, severe kidney disease, during pregnancy, or in premature babies or children under 6 weeks old.

Also see list of precautions and interactions


Store below 25°C in a dry place.


Trimethoprim is used to treat bacterial infections.

It is an antibacterial medication, sometimes known as an antibiotic.

It is used to prevent the growth of bacteria that are causing an infection.

In general this drug is used to treat a wide range of infections including urinary tract infections and respiratory tract infections and for the long-term prevention of recurrent urinary tract infections. It is also used in the treatment of pneumocystis pneumonia. Trimethoprim is often prescribed in combination with another antibacterial medication, sulfamethoxazole. In this combination form it is known as co-trimoxazole.

Benefits of being on this drug can include controlling and stopping urinary tract and respiratory tract infections and with long-term use, preventing repeated occurrences of urinary tract infections. In controlling or preventing infections, trimethoprim may reduce some of the symptoms of such infections such as a frequent urge to urinate and a painful, burning feeling during urination (urinary tract infections) or coughing, wheezing, and breathlessness (respiratory tract infections).

Listed below are the typical uses of trimethoprim.

  • Treatment of urinary tract infections
  • Treatment of acute and chronic bronchitis
  • Treatment of pneumocystis pneumonia


How often do I take it?

  • Take this medication orally usually twice each day (with a glass of water) for an acute infection or once each day for prevention of repeat infections.
  • Use this medication for the duration of the prescribed course of treatment in order to get the most benefit from it.
  • Remember to use it at the same time each day - unless specifically told otherwise by your doctor.
  • Certain medical conditions may require different dosage instructions as directed by your doctor.

What dose?

  • Dosage is based on your age, gender, medical condition, response to therapy, and use of certain interacting medicines.

Do I need to avoid anything?

  • There is no need to avoid alcohol or particular foods or to avoid driving or using machinery. However, if the drug causes you to feel sleepy then avoid driving or using machinery. However, if you have any concerns about driving or using machinery whilst using this medicine consult your doctor or pharmacist for advice.

When can I stop?

  • Always complete the full course as prescribed by your doctor. It is important to continue taking this medication even if you feel well, or the infection may come back.


Known side effects:

Rarely reported side effects include:

If any of these persist or you consider them severe then stop taking the medication and inform your doctor.

Tell your doctor immediately if you develop any of the following symptoms:

  • Allergic reaction such as swelling of the face, lips, tongue or throat, difficulty breathing, shock, or collapse.
  • Aseptic meningitis, which 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.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

The Yellow Card Scheme allows you to report suspected side effects from any type of medicine (which includes vaccines, herbals and over the counter medicines) that you are taking. It is run by the medicines safety watchdog called the Medicines and Healthcare products Regulatory agency (MHRA). Please report any suspected side effect on the Yellow Card Scheme website.


Before taking trimethoprim, tell your doctor or pharmacist if you are allergic to it; or to co-trimoxazole; or if you have any other allergies.

This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: blood dyscrasias (abnormality of the blood, such as low white blood cell count, low red blood cell count or low platelet count).

Before using this medication, tell your doctor or pharmacist your medical history, especially any of the following: renal (kidney) impairmentliver disease, folate deficiency, acute porphyria.

Before having surgery, tell your doctor or dentist that you are taking this medication.

Does alcohol intake affect this drug?

  • No.

The elderly: trimethoprim should be used with caution in the elderly because renal (kidney) function may be impaired.

Pregnancy and breastfeeding - please ensure you read the detailed information below


Trimethoprim is not safe to take if you are, or are planning to become, pregnant.

Ask your doctor or pharmacist if you have any doubts or questions about this.

First trimester: avoid
Second trimester: avoid
Third trimester: avoid

It is sensible to limit use of medication during pregnancy whenever possible. However, your doctor may decide that the benefits outweigh the risks in individual circumstances and after a careful assessment of your specific health situation.

If you have any doubts or concerns you are advised to discuss the medicine with your doctor or pharmacist.


Trimethoprim passes into breast milk. However, short term use is not known to be harmful.

Ask your doctor or pharmacist if you have any doubts or questions about this.

It is sensible to limit use of medication during breastfeeding whenever possible. However, your doctor may decide that the benefits outweigh the risks in individual circumstances and after a careful assessment of your specific health situation.

If you have any doubts or concerns you are advised to discuss the medicine with your doctor or pharmacist.


Before using this medicine, tell your prescriber of all the medicines you are taking including prescription medicines and medicines you have bought over the counter without a prescription. Tell your prescriber if you are taking vitamins or complementary remedies such as herbal products, as these can also interact with medicines.

If you are taking more than one medicine, these may interact with each other. Your prescriber may decide to use medicines which interact with each other if the benefit outweighs the risks. In these cases, the dose of your medicines may need to be adjusted or you may be monitored more closely.

The following medicines may interact with trimethoprim:

  • Warfarin
  • Antibiotics such as rifampicin and dapsone
  • Azathioprine (an immunosuppressant)
  • Ciclosporin (to prevent rejection after transplantation)
  • Digoxin (to treat heart conditions)
  • Eplerenone (a diuretic)
  • Methotrexate and mercaptopurine (cytotoxics)
  • Phenytoin (to treat epilepsy)
  • Pyrimethamine (to treat malaria)
  • Repaglanide (for diabetes)
  • Bone marrow depressants

This information does not contain all possible interactions. Therefore, tell your prescriber of all the products you are using before taking this medicine.

If you have a question or want to discuss anything about your medicine, speak to your local pharmacist.


If you think you, or someone you care for, might have accidentally taken more than the recommended dose of trimethoprim or intentional overdose is suspected, contact your local hospital, GP or if in England call NHS 111. In Scotland call NHS 24. In Wales, call NHS Direct Wales. In the case of medical emergencies, always dial 999.


If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

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CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgement of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse events, nor should it be construed to indicate that use of a particular medicine is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any medicine, changing any diet, or discontinuing any course of treatment.

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