Primsol (trimethoprim)

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

  • Medical and Pharmacy Editor: Jay W. Marks, MD
    Jay W. Marks, MD

    Jay W. Marks, MD

    Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

What is the dosage for Primsol (trimethoprim)?

  • The usual dose is 100 mg every 12 hours or 200 mg every 24 hours for 10 days.
  • As with all antibiotics, it is important to complete the entire course of Primsol even if symptoms improve early during therapy.
  • Persons with kidney diseases may need to receive lower doses since diseased kidneys may not eliminate Primsol adequately from the body, and levels of Primsol may increase in the body and lead to side effects.

Which drugs or supplements interact with Primsol (trimethoprim)?

  • Changes in one patient's mental status occurred when a combination of trimethoprim and sulfamethoxazole was given with amantadine (Symmetrel).
  • Blood levels of phenytoin (Dilantin) may be increased by treatment with trimethoprim. This may lead to side effects of phenytoin such as dizziness, and reduced attention.
  • Trimethoprim also may increase blood levels of digoxin (Lanoxin) and warfarin (Coumadin, Jantoven) and lead to serious toxic effects.
  • Anemia, due to a reduction in folic acid, can occur in persons receiving trimethoprim in combination with:
  • The combination of trimethoprim and cyclosporine can increase the risk of kidney damage from cyclosporine. When trimethoprim and dapsone are used together, increased blood concentrations of both drugs can occur, sometimes with side effects that include a toxic condition of the blood called methemoglobinemia.
  • Rifampin can increase the elimination of trimethoprim by the kidneys and may reduce the effectiveness of trimethoprim.

Is Primsol (trimethoprim) safe to use during pregnancy or while breastfeeding?

  • Although there are no human studies that have examined the effects of trimethoprim on the fetus, animal studies have shown adverse effects. Therefore, the physician must weigh the potential risks to the fetus against the potential benefits to the mother when considering trimethoprim therapy for pregnant women.
  • Trimethoprim is secreted into breast milk in high concentrations. Use of trimethoprim by mothers who are breast-feeding should be avoided.

What else should I know about Primsol (trimethoprim)?

What preparations of Primsol (trimethoprim) are available?
  • Tablets: 100 and 200 mg.
  • Solution: 50 mg/5 ml
How should I keep Primsol (trimethoprim) stored?
  • Tablets should be stored at room temperature, 15 C - 30 C (59 F - 86 F).
When was Primsol (trimethoprim) approved by the FDA?
  • Trimethoprim was first approved by the FDA in combination with sulfamethoxazole (for example, Bactrim, Septra) in 1973.
  • Trimethorpim was approved as a stand-alone drug in 1980.

Reference: FDA Prescribing Information

Medically Reviewed by a Doctor on 11/18/2016

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