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Trimethoprim Side Effects

For the Consumer

Applies to trimethoprim: oral solution, oral tablet

Side effects requiring immediate medical attention

Along with its needed effects, trimethoprim may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking trimethoprim:

Less common


  • Black, tarry stools
  • blood in urine or stools
  • bluish fingernails, lips, or skin
  • changes in facial skin color
  • chills
  • difficult breathing or shortness of breath
  • fever with or without chills
  • general feeling of discomfort or illness
  • headache
  • joint or muscle pain
  • nausea
  • neck stiffness
  • pale skin
  • pinpoint red spots on skin
  • redness, blistering, burning, tenderness, peeling, or loosening of skin or mucous membranes
  • redness, swelling, or soreness of tongue
  • red skin lesions, often with a purple center
  • sore throat
  • swelling
  • thickened or scaly skin
  • unusual bleeding or bruising
  • unusual tiredness or weakness

Side effects not requiring immediate medical attention

Some side effects of trimethoprim may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

For Healthcare Professionals

Applies to trimethoprim: compounding powder, oral solution, oral tablet


Common (1% to 10%): Rash (e.g., maculopapular, morbilliform, pruritic), pruritus

Rare (less than 0.1%): Photosensitivity, angioedema, erythema multiforme, Stevens Johnson syndrome, toxic epidermal necrolysis (Lyell Syndrome

Frequency not reported: Exfoliative dermatitis, urticaria[Ref]


Common (1% to 10%): Epigastric distress, nausea, vomiting, glossitis, abdominal pain, sore mouth

Frequency not reported: Pseudomembranous colitis, Clostridium difficile associated diarrhea[Ref]


Frequency not reported: Thrombocytopenia, leukopenia, neutropenia, megaloblastic anemia, methemoglobinemia[Ref]


Rare (less than 0.1%): Cholestatic jaundice

Frequency not reported: ALT and AST elevations, elevated bilirubin[Ref]


Rare (less than 0.1%): Anaphylaxis[Ref]


Frequency not reported: Hyperkalemia, hyponatremia[Ref]


Frequency not reported: Myalgia[Ref]

Nervous system

Rare (less than 0.1%): Aseptic meningitis, headache[Ref]


Frequency not reported: Fever[Ref]


Frequency not reported: Increased BUN, increased serum creatinine[Ref]


1. "Product Information. Trimethoprim (trimethoprim)." Teva Pharmaceuticals USA, North Wales, PA.

2. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

3. Cerner Multum, Inc. "Australian Product Information." O 0

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

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