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

• Known hypersensitivity to the drug.
• Severe liver or kidney impairment.
• Significant blood disorders like megaloblastic anemia due to folate deficiency.
• Not recommended during the first trimester of pregnancy unless clearly needed.

Possible Side Effects

• Common: Nausea, vomiting, rash, and itching.
• Serious: Blood disorders (like leukopenia), liver enzyme elevation, Stevens-Johnson syndrome.

Seek immediate medical help for signs of allergic reaction, such as swelling or breathing difficulty.

Drug Interaction

• Methotrexate (increased toxicity).
• Phenytoin (prolonged half-life).
• 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.
• Do not use expired medication.

Disclaimer

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