What is Trimethoprim: Uses, Warnings & Interactions

Updated May 14, 2025  •  Published Dec 30, 2020

Trimethoprim overview

BRAND NAMES:

  • Trimpex Solution, Primsol

Generic Names:

  • Trimethoprim

Uses:

  • Treats infections, including urinary tract infections and ear infections.

Therapeutic Classes:

  • Antibiotic, Antiseptic

Forms:

  • Liquid, Tablet

How it’s taken:

  • By mouth

What is Trimethoprim used for?

Trimethoprim is an antibiotic used to treat bacterial infections. It stops the growth and spread of bacteria in the body. Trimethoprim treats only bacterial infections and will not work for treating viral infections such as the cold or flu. Trimethoprim also treats ear, bladder, and kidney infections caused by certain bacterias.

What form(s) does Trimethoprim come in

  • Liquid

  • Tablet

What are common Trimethoprim doses?

  • Tablet 100MG

Common Trimethoprim prescriptions

  • Trimethoprim
    100mg tablet

How to take Trimethoprim

  • Your doctor will tell you how much medicine to use. Do not use more than directed.

  • Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup.

  • You may take your medicine with food to avoid stomach upset.

  • Take all of the medicine in your prescription to clear up your infection, even if you feel better after the first few doses.

  • Your doctor will tell you how much medicine to use. Do not use more than directed.

  • Take all of the medicine in your prescription to clear up your infection, even if you feel better after the first few doses.

  • Measure the oral liquid medicine with a marked measuring spoon, oral syringe, or medicine cup.

  • You may take your medicine with food to avoid stomach upset.

What to do if you miss a dose of Trimethoprim

  • Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.

  • Ask your pharmacist, doctor, or health caregiver about the best way to dispose of any outdated medicine or medicine no longer needed.

  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Trimethoprim contraindications

  • You should not use this medicine if you have had an allergic reaction to trimethoprim, or if you have a certain type of anemia.

Trimethoprim warnings

  • Make sure your doctor knows if you are pregnant or breast feeding, or if you have liver or kidney disease.

  • Tell any doctor or dentist who treats you that you are using this medicine. This medicine may affect certain medical test results.

  • Swollen or sore tongue.

  • Unexplained fever or sore throat.

  • Unusual bleeding or bruising.

Trimethoprim interactions

  • Make sure your doctor knows if you are using phenytoin (Dilantin®).

  • Tell any doctor or dentist who treats you that you are using this medicine. This medicine may affect certain medical test results.

Trimethoprim side effects

Serious Side Effects

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing

  • Severe rash, hives, or itching.

  • Unexplained fever or sore throat.

  • Unusual bleeding or bruising.

  • Swollen or sore tongue.

Less Serious Side Effects

  • Nausea, diarrhea, or vomiting.

  • Muscle twitching.

Subscribe to our savings newsletter

Health education, drug info, wellness & more

By clicking 'Subscribe', I agree to SingleCare's Terms & Conditions.