Active Ingredient

Trimethoprim

Trimethoprim is an antibacterial medication commonly used to treat bacterial infections. It is often prescribed for infections of the urinary tract and other specific types of infections.

By targeting bacteria, it helps to alleviate symptoms and clear the infection.

Written By Douglas C. Goldberg, MD

Reviewed By Philip Schein, MD

Last Updated 28 Nov 2025

Trimethoprim Uses

Trimethoprim is used to treat a variety of bacterial infections. It is effective in managing:

Urinary tract infections
Acute bronchitis
Traveler’s diarrhea
Shigellosis
Bacterial prostatitis

How Trimethoprim Works

Trimethoprim works by inhibiting the growth of bacteria. It does this by blocking a specific bacterial enzyme that is crucial for their survival.

As a result, the bacteria are unable to produce essential proteins, which stops them from multiplying and spreading.

This action helps your body’s immune system to eliminate the infection more effectively.

Common side effects of Trimethoprim

Not everyone experiences side effects from Trimethoprim, and many are mild and temporary. Common side effects include:

Nausea
Vomiting
Rash
Itching
Stomach upset
Diarrhea

If you experience serious or persistent symptoms, contact your doctor.

Inform your doctor about any allergies or medical conditions before starting Trimethoprim.
Avoid consuming large amounts of alcohol while taking this medication.
Monitor for any signs of an allergic reaction, such as rash or itching.
Do not take this medication if you have a known folate deficiency without consulting your doctor.
Stay hydrated and maintain a balanced diet during treatment.

Always consult your doctor for personalized advice and before making any changes to your medication routine.

Frequently Asked Questions

What is Trimethoprim used for?

Trimethoprim is used to treat bacterial infections such as urinary tract infections and bronchitis.

How long does it take for Trimethoprim to work?

The effects of Trimethoprim can vary, but improvement in symptoms is often seen within a few days of starting treatment.

Can I drink alcohol while taking Trimethoprim?

It is advisable to limit alcohol consumption while taking Trimethoprim, as alcohol can increase the risk of side effects.

Are there any foods I should avoid while taking Trimethoprim?

There are no specific foods to avoid, but maintaining a balanced diet and staying hydrated is recommended.

Can Trimethoprim cause allergic reactions?

Yes, Trimethoprim can cause allergic reactions in some people. If you experience symptoms like rash or itching, seek medical advice.