Generic Trimethoprim

Common Use
Trimethoprim is an antibiotic primarily used to treat urinary tract infections (UTIs). It may also be prescribed for respiratory infections, traveler’s diarrhea, or prophylaxis in patients with frequent infections. It works by inhibiting bacterial DNA synthesis by blocking folic acid production.

Dosage and Direction
Trimethoprim is usually taken orally once or twice daily, with or without food. The typical adult dose for UTIs is 100 mg twice daily or 200 mg once daily, for 3–14 days depending on severity. Take the medication at evenly spaced intervals and complete the full course even if symptoms improve early.

Precautions
Inform your doctor if you have kidney or liver disease, folate deficiency, blood disorders, or if you are pregnant. Drink plenty of fluids during treatment to help prevent kidney complications. Monitoring may be needed for long-term use, especially in elderly or immunocompromised patients.

Contraindications
Trimethoprim is contraindicated in patients with known hypersensitivity to the drug, severe liver or kidney impairment, or significant blood disorders like megaloblastic anemia due to folate deficiency. It is not recommended during the first trimester of pregnancy unless clearly needed.

Possible Side Effects
Common side effects include nausea, vomiting, rash, and itching. Less common but serious effects include blood disorders (like leukopenia), liver enzyme elevation, and Stevens-Johnson syndrome. Seek immediate medical help for signs of allergic reaction, such as swelling or breathing difficulty.

Drug Interaction
Trimethoprim can interact with methotrexate (increased toxicity), phenytoin (prolonged half-life), and potassium-sparing diuretics (risk of hyperkalemia). Monitor electrolytes and blood counts if using with other medications affecting the kidneys or bone marrow.

Missed Dose
If you miss a dose, take it as soon as possible. If it’s almost time for the next dose, skip the missed one—do not double the dose.

Overdose
Overdose symptoms may include nausea, vomiting, dizziness, confusion, and bone marrow suppression. Seek medical attention immediately if overdose is suspected.

Storage
Store at room temperature away from heat, moisture, and direct sunlight. Keep out of reach of children and do not use expired medication.

Disclaimer

We provide only general information about medications which does not cover all directions, possible drug integrations, or precautions. Information at the site cannot be used for self-treatment and self-diagnosis. Any specific instructions for a particular patient should be agreed with your health care adviser or doctor in charge of the case. We disclaim reliability of this information and mistakes it could contain. We are not responsible for any direct, indirect, special or other indirect damage as a result of any use of the information on this site and also for consequences of self-treatment.

Clinical Verification

Last Clinically Updated: August 15, 2026

Written By

Dr. Elena Vance, PharmD

Clinical Specialist in Neuropharmacology

Fact Checked By

Marcus Thorne, MS

Biomedical Data & FDA Label Verification

Medically Reviewed By

Dr. Arthur Campbell, MD

Board-Certified Psychiatrist (ABPN)