Primsol Side Effects

Generic Name: trimethoprim

Note: This page contains side effects data for the generic drug trimethoprim. It is possible that some of the dosage forms included below may not apply to the brand name Primsol.

It is possible that some side effects of Primsol may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

For the Consumer

Applies to trimethoprim: oral solution, oral tablet

As well as its needed effects, trimethoprim (the active ingredient contained in Primsol) may cause unwanted side effects that require medical attention.

If any of the following side effects occur while taking trimethoprim, check with your doctor immediately:

Less common
  • Skin rash or itching
  • 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

Some trimethoprim side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

Less common
  • Diarrhea
  • loss of appetite
  • nausea or vomiting
  • stomach cramps or pain

For Healthcare Professionals

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


The incidence of rash was 2.9% to 6.7% at recommended doses of 200 mg/day.

A higher incidence of rash was reported in clinical trials using large doses of trimethoprim (the active ingredient contained in Primsol) These rashes had an onset of 7 to 14 days after begin of therapy and were maculopapular, morbilliform, pruritic, and mild to moderate in severity.

One case report described Stevens-Johnson syndrome, arthritis, and uveitis associated with trimethoprim.

Common (1% to 10%): Rash (up to 6.7%)
Rare (less than 0.1%): Stevens-Johnson syndrome, exfoliative dermatitis, erythema multiforme, toxic epidermal necrolysis (Lyell syndrome)
Frequency not reported: Pruritus, phototoxic skin eruptions


Common (1% to 10%): Diffuse, often pruritic, maculopapular or urticarial rashes (up to 7%)
Rare (less than 0.1%): Anaphylaxis, diffuse pneumonitis
Frequency not reported: Fixed drug eruption, linear fixed drug eruption

A Dutch retrospective analysis identified 13 cases of probable or possible anaphylaxis with a probable or definite causal relationship to trimethoprim.


Rare cases of Clostridium difficile pseudomembranous colitis have been reported during or after trimethoprim (the active ingredient contained in Primsol) therapy.

Frequency not reported: Epigastric distress, nausea, vomiting, glossitis, Clostridium difficile associated diarrhea, mild abdominal distress, pseudomembranous colitis


Since trimethoprim (the active ingredient contained in Primsol) inhibits a step of folate synthesis in vivo, megaloblastic anemia was more likely in patients with folate deficiency, such as alcoholics, the malnourished, and in patients with chronic hemolytic anemia.

Frequency not reported: Leukopenia, megaloblastic anemia, methemoglobinemia, neutropenia, thrombocytopenia


Frequency not reported: Hyperkalemia, hyponatremia


Trimethoprim may inhibit renal tubular creatinine secretion, resulting in increased serum levels. Some data indicated a significant decrease in creatinine clearance associated with trimethoprim (the active ingredient contained in Primsol) These changes appeared to be completely reversible upon discontinuation of therapy.

Trimethoprim acts like amiloride and blocks apical membrane sodium channels in the distal nephron. This resulted in inhibition of potassium secretion and mild hyperkalemia in some cases. Up to 20% of patients with AIDS who were given trimethoprim-sulfamethoxazole developed mild hyperkalemia due to the effect of trimethoprim, not sulfamethoxazole, on the kidney.

Frequency not reported: Increased BUN, increased serum creatinine levels, renal tubular creatinine secretion inhibited, decreased creatinine clearance, aldosterone-antagonistic effect in the renal tubule

Nervous system

Trimethoprim-induced aseptic meningitis was characterized by a sterile cerebral spinal fluid pleocytosis (usually lymphocytic) associated with meningismus. Trimethoprim-associated aseptic meningitis, like that associated with some nonsteroidal anti-inflammatory medications, may be more likely in patients with underlying connective tissue diseases, such as systemic lupus erythematosus or Sjogren's syndrome. Occult bacterial, viral, and atypical etiologies of meningitis must also be considered. Cases of aseptic meningitis have been reported in AIDS patients.

Rare (less than 0.1%): Aseptic meningitis


Rare (less than 0.1%): Cholestatic jaundice
Frequency not reported: Elevated serum transaminases, elevated bilirubin


Frequency not reported: Fever


One case report described Stevens-Johnson syndrome, arthritis, and uveitis associated with trimethoprim (the active ingredient contained in Primsol)

Rare (less than 0.1%): Arthritis (at least 1 case)


One case report described Stevens-Johnson syndrome, arthritis, and uveitis associated with trimethoprim (the active ingredient contained in Primsol)

Rare (less than 0.1%): Uveitis (at least 1 case)

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