Last updated on RxList: 3/1/2021

What is Trimethoprim and how is it used?

Trimethoprim is a prescription medicine used to treat the symptoms of bacterial infections. Trimethoprim may be used alone or with other medications.

Trimethoprim belongs to a class of drugs called Antibiotics, Other.

It is not known if Trimethoprim is safe and effective in children younger than 12 years of age.

What are the possible side effects of Trimethoprim?

Trimethoprim may cause serious side effects including:

  • new signs of infection (sore throat),
  • easy bruising or bleeding,
  • pale skin,
  • unusual tiredness,
  • fast or irregular heartbeat,
  • mood changes,
  • nausea,
  • vomiting,
  • dark urine,
  • stomach pain,
  • yellowing of the skin or eyes (jaundice),
  • stiff neck,
  • headache,
  • muscle weakness,
  • extreme drowsiness,
  • sudden sweating,
  • shaking,
  • hunger,
  • blurred vision,
  • dizziness, and
  • tingling hands or feet

Get medical help right away, if you have any of the symptoms listed above.

The most common side effects of Trimethoprim include:

  • itching,
  • rash,
  • diarrhea,
  • nausea,
  • vomiting,
  • stomach upset,
  • loss of appetite,
  • changes in taste,
  • headache,
  • skin sensitivity to sunlight,
  • swollen tongue, and
  • fever

Tell the doctor if you have any side effect that bothers you or that does not go away.

These are not all the possible side effects of Trimethoprim. For more information, ask your doctor or pharmacist.

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


Trimethoprim (trimethoprim tablet) is a synthetic antibacterial available as 100 mg tablets for oral administration.

Trimethoprim (trimethoprim tablet) is 2,4-Diamino-5-(3,4,5-trimethoxybenzyl) pyrimidine. It is a white to cream colored, odorless, bitter compound. The structural formula is represented below:

Trimethoprim Structural Formula Illustration

Trimethoprim (trimethoprim) Tablets USP, 100 mg contain the following inactive ingredients: anhydrous lactose, colloidal silicon dioxide, magnesium stearate, sodium lauryl sulfate, sodium starch glycolate and stearic acid.