What is trimethoprim used for?

  • Trimethoprim, thanks to its bactericidal action mechanism, inhibits bacterial growth by interfering with the synthesis of nucleic acids, preventing their growth and development, thus eliminating infections caused in certain organs of the human body . 
  • It is used to treat: 

Dosage and routes of administration of trimethoprim

Trimethoprim comes as tablets, usually containing a strength of 100 mg. The administration is orally and the posology as a reference can be the following:

  • Tablets: The usual dose is one 100 mg tablet every 12 hours, which can be taken with or without food. According to the medical diagnosis this dose may vary.
  • Urinary infection : Children ≥ 2 months of age, from 4 to 6 mg/kg/day, every 12 hours. Children ≥ 12 years of age and adults 100 mg every 12 hours or 200 mg every 24 hours.
  • Urinary tract infection prophylaxis : 100 mg daily.

What products contain trimethoprim?

Some of the medicines that contain trimethoprim are:

  • Septrin®
  • Soltrim®
  • Bactiver®
  • Neolag®


  • Septrin® is a medicine that contains the combination of trimethoprim and sulfamethoxazole, which comes in the form of tablets in a concentration of 80 mg of trimethoprim and 400 mg of sulfamethoxazole.
  • It is indicated for the treatment of urinary tract infections , acute otitis media. among other diseases.


  • Soltrim® is the brand name of a combination drug in the form of powder and solution for solution for injection, which contains 160 mg of trimethoprim and lyophilized powder containing 800 mg of sulfamethoxazole.
  • It is indicated in the treatment of pneumonia, pharyngitis and nocardiosis .
  • If you need to know more about this medicine, see What is soltrim and what is it used for? .


  • The bactiver® is an antibiotic medicine, which contains 40/200 mg/5 ml in suspension with trimethoprim and sulfamethoxazole.
  • It is used in the treatment of acute otitis media , acute exacerbations of chronic bronchitis, acute uncomplicated infections of the urinary tract.
  • For more information about this medicine, see Bactiver: What is it and what is it for? .


  • Neolag® is a combination drug containing dexamethasone , sodium phosphate 5.0 mg, polymyxin B sulfate 50,000 IU and trimethoprim 5.0 mg.
  • It is indicated for the treatment of acute bacterial conjunctivitis , blepharitis and blepharoconjunctivitis.

Trimethoprim Side Effects

Clinical data indicate that therapeutic treatment with trimethoprim may cause some of the following adverse effects in a certain patient population:

  • Possible allergic reactions due to contact with any component of the formula.
  • Erythema multiforme, exfoliative dermatitis and pruritus.
  • Cutaneous phototoxicity, Stevens-Johnson syndrome .
  • Aseptic meningitis, fever and headache.
  • Toxic epidermal necrolysis.
  • Epigastric discomfort, anemia , glossitis, nausea and vomiting .
  • Maculopapular rash, hyperkalemia, hyponatremia.

Important: Stop treatment and notify your doctor if any of these symptoms or others not listed appear while taking this drug.

Contraindications and warnings of trimethoprim

The use of trimethoprim is contraindicated in the following cases:

  • Hypersensitivity to the components of the formula.
  • Patients with blood dyscrasias.
  • People with megaloblastic anemia due to folic acid deficiency .
  • Premature patients and those less than 2 months old.
  • If you are being medicated with other drugs for other pathologies, without consulting the doctor.
  • Patients with renal or hepatic insufficiency.
  • During the pregnancy period.
  • During breastfeeding .

You should know: Before starting treatment with trimethoprim, provide all information about your medical history to your doctor.

Avoid it if you have:

  • Hypersensitivity to trimethoprim.
  • Folic acid deficiency.


  • Pharmaceutical products such as trimethoprim must be administered with a prescription or prescription.
  • Its prolonged use can cause a fungal or bacterial superinfection.
  • Particular caution should be exercised in patients with renal insufficiency and hepatic insufficiency.
  • Likewise, elderly patients and patients undergoing chronic anticonvulsant treatments should be constantly monitored.
  • Keep this medicine out of the reach of children.

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