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Trimethoprim Side Effects

Medically reviewed by Last updated on May 23, 2023.

Applies to trimethoprim: oral solution, oral tablet.

Serious side effects of Trimethoprim

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

Other side effects of Trimethoprim

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.


The most common side effects were pruritus, rash, and mild gastrointestinal disturbances (including nausea, vomiting, glossitis); these effects were generally mild and reversed quickly when the drug was stopped.[Ref]


Very common (10% or more): Hyperkalemia

Very rare (less than 0.01%): Hypoglycemia, hyponatremia, anorexia[Ref]

Hyperkalemia has been reported, particularly in elderly patients and patients with HIV.[Ref]


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

Very rare (less than 0.01%): Photosensitivity, angioedema, exfoliative dermatitis, fixed drug eruption, erythema multiforme, erythema nodosum, Stevens-Johnson syndrome, toxic epidermal necrolysis (Lyell's Syndrome), bullous dermatitis, purpura, allergic vasculitis (resembling Henoch-Schonlein purpura)

Frequency not reported: Pruritus, phototoxic skin eruptions[Ref]

Rash was generally mild to moderate and appeared 7 to 14 days after starting therapy.[Ref]


Common (1% to 10%): Nausea, diarrhea, vomiting

Very rare (less than 0.01%): Constipation, glossitis, stomatitis, pseudomembranous colitis, pancreatitis

Frequency not reported: Epigastric distress, sore mouth, gastrointestinal disturbances, abdominal pain, Clostridioides difficile-associated diarrhea[Ref]

Nervous system

Common (1% to 10%): Headache

Very rare (less than 0.01%): Dyskinesias, aseptic meningitis, tremor, ataxia, dizziness, lethargy, syncope, paresthesia, convulsions, peripheral neuritis, vertigo, tinnitus[Ref]

Aseptic meningitis reversed rapidly when this drug was stopped but recurred in a number of cases upon re-exposure to sulfamethoxazole-trimethoprim or this drug alone.[Ref]


Common (1% to 10%): Monilial overgrowth

Very rare (less than 0.01%): Drug fever

Frequency not reported: Fever[Ref]


Fatalities have been reported (especially in elder patients or patients with renal or liver dysfunction), but most hematological changes were mild and reversed when therapy was stopped.[Ref]

Very rare (less than 0.01%): Thrombocytopenia, leukopenia, neutropenia, pancytopenia, bone marrow depression, agranulocytosis, aplastic anemia, hemolytic anemia, eosinophilia, purpura, hemolysis

Frequency not reported: Megaloblastic anemia, methemoglobinemia, depression of hematopoiesis, hematological changes[Ref]


Fatalities have been reported with cholestatic jaundice and hepatic necrosis.[Ref]

Very rare (less than 0.01%): Disturbance in liver enzymes, elevated serum transaminases, elevated bilirubin, cholestatic jaundice, hepatic necrosis

Frequency not reported: Elevated ALT, elevated AST[Ref]


Very rare (less than 0.01%): Hypersensitivity, anaphylaxis, anaphylactoid reaction[Ref]


Very rare (less than 0.01%): Depression, hallucinations, confusional states, agitation, anxiety, abnormal behavior, insomnia, nightmares[Ref]


Very rare (less than 0.01%): Cough, shortness of breath, wheeze, epistaxis[Ref]


Very rare (less than 0.01%): Myalgia, arthralgia, systemic lupus erythematosus[Ref]


Very rare (less than 0.01%): Impaired renal function (including renal failure)

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

Whether increased BUN and serum creatinine were due to inhibition of creatinine tubular secretion or genuine renal dysfunction was not established.[Ref]


Very rare (less than 0.01%): Hematuria[Ref]


Very rare (less than 0.01%): Periarteritis nodosa[Ref]


Very rare (less than 0.01%): Uveitis[Ref]

Frequently asked questions


1. Cerner Multum, Inc. UK Summary of Product Characteristics.

2. Cerner Multum, Inc. Australian Product Information.

3. Product Information. Trimethoprim (trimethoprim). Teva Pharmaceuticals USA. 2016.

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.