Last updated on RxList: 8/5/2019
Primsol Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

Last reviewed on RxList 8/5/2019

Primsol (trimethoprim hydrochloride oral solution) is an antibacterial solution indicated for the treatment of infections caused by susceptible strains of the designated microorganisms in the following conditions: acute otitis media due to susceptible strains of Streptococcus pneumoniae and Haemophilus influenza, and treatment of initial episodes of uncomplicated urinary tract infections due to susceptible strains of: Escherichia coli, Proteus mirabilis, Klebsiella pneumoniae, Enterobacter species and coagulase-negative Staphylococcus species, including S. saprophyticus. Common side effects of Primsol include:

  • abdominal pain
  • diarrhea
  • vomiting, and
  • rash

The recommended dose of Primsol for pediatric patients with acute otitis media is 10 mg/kg trimethoprim per 24 hours, given in divided doses every 12 hours for 10 days. The usual oral adult dosage of Primsol to treat urinary tract infections is 100 mg (10 mL) every 12 hours or 200 mg (20 mL) every 24 hours, each for 10 days. Primsol may interact with phenytoin. Tell your doctor all medications and supplements you use. During pregnancy, Primsol should be taken only if prescribed. Primsol may interfere with folic acid metabolism. Primsol passes into breast milk and may interfere with folic acid metabolism. Consult your doctor before breastfeeding.

Our Primsol (trimethoprim hydrochloride oral solution) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


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Primsol Consumer Information

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Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • severe stomach pain, diarrhea that is watery or bloody (even if it occurs months after your last dose);
  • pale, gray, or bluish skin;
  • fever, weakness;
  • sore or swollen tongue;
  • easy bruising, purple or red spots under your skin;
  • a skin rash, no matter how mild; or
  • high potassium level--nausea, weakness, tingly feeling, chest pain, irregular heartbeats, loss of movement.

Common side effects may include:

  • vomiting, diarrhea, stomach pain;
  • rash, itching; or
  • swelling in your tongue.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Primsol (Trimethoprim Hydrochloride Oral Solution)


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To report SUSPECTED ADVERSE REACTIONS, contact FSC Laboratories , Inc. at 1-866-764- 7822, or FDA at 1-800-FDA-1088 or

Adverse Events Reported During Pediatric Clinical Trials With PRIMSOL

The following table lists those drug-related adverse events reported most frequently during the clinical trials in pediatric patients aged 6 months to 12 years. Most of these events were determined to be mild. The incidence of drug-related adverse events was significantly lower for PRIMSOL, which was most apparent for those events related to skin/appendages as a body system.

Drug-related Adverse Event Percent of Pediatric Patients
Body as a whole
  abdominal pain < 1 2.5
Digestive system
  diarrhea 4.2 4.6
  vomiting 1.6 1.5
  rash 1.3 6.1
* sulfamethoxazole + trimethoprim oral suspension

An increase in lymphocytes and eosinophils was noted in some pediatric patients following treatment with PRIMSOL or sulfamethoxazole + trimethoprim oral suspension.

Adverse Reactions Reported For Trimethoprim

In addition to the adverse events listed above which have been observed in pediatric patients receiving PRIMSOL, the following adverse reactions and altered laboratory tests have been previously reported for trimethoprim and therefore, may occur with PRIMSOL therapy:

Dermatologic reactions: pruritus and exfoliative dermatitis. At the recommended adult dosage regimens of 100 mg b.i.d., or 200 mg q.d., each for 10 days, the incidence of rash is 2.9% to 6.7%. In clinical studies which employed high doses of trimethoprim in adults, an elevated incidence of rash was noted. These rashes were maculopapular, morbilliform, pruritic and generally mild to moderate, appearing 7 to 14 days after the initiation of therapy.

Gastrointestinal reactions: Epigastric distress, nausea, and glossitis.

Hematologic reactions: Thrombocytopenia, leukopenia, neutropenia, megaloblastic anemia and methemoglobinemia.

Metabolic reactions: Hyperkalemia, hyponatremia.

Miscellaneous reactions: Fever, elevation of serum transaminase and bilirubin, and increases in BUN and serum creatinine levels.

Read the entire FDA prescribing information for Primsol (Trimethoprim Hydrochloride Oral Solution)

© Primsol Patient Information is supplied by Cerner Multum, Inc. and Primsol Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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