Examples

How It Works

This antibiotic, which usually comes in pill or tablet form that you take by mouth (orally), kills the bacteria that commonly cause urinary tract infections (UTIs).

Why It Is Used

Trimethoprim is usually used with a sulfonamide to treat a UTI. If you are allergic to sulfa drugs, your doctor may prescribe trimethoprim by itself.

Trimethoprim treats uncomplicated urinary tract infections. These are UTIs that are not caused by an obstruction or structural problem or some other medical condition that affects urinary function, such as diabetes.

Trimethoprim can be used to prevent recurrent urinary tract infections.

How Well It Works

With trimethoprim treatment, you can expect relief of symptoms of a UTI within 2 to 3 days.

When taken as preventive therapy, trimethoprim also reduces the number of recurrent UTIs. But antibiotic studies show that this kind of therapy is short-acting-when you stop taking an antibiotic, your risk of getting a UTI is likely to go up again.¹

Side Effects

Common side effects are:

• Skin rashes.
• Upset stomach.
• Altered taste.
• Nausea.

Rare but serious side effects include destruction of red blood cells.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Take trimethoprim medication 1 to 2 hours before or after meals. Drink extra fluids while you are taking this medication.

You can take trimethoprim for either 3 or 7 days to treat an uncomplicated bladder infection. In most people, a 3-day dose of this antibiotic is as effective as a 7-day dose.²

Antibiotic resistance

Be sure to take all of the medication your doctor gives you, even if you are feeling better. If you do not take all of your antibiotics as prescribed, the infection may return. Not taking the full course of antibiotics also encourages the development of bacteria that are resistant to antibiotics. This makes antibiotics less effective and bacterial infections more difficult to treat. Antibiotic-resistance among bacteria that cause UTIs increased steadily in recent decades. You and your doctor may have to try different antibiotics, and different combinations of antibiotics, to find the right medication that will kill the bacteria causing your UTI.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.

Citations

1. Sen A (2006). Recurrent cystitis in non-pregnant women. Clinical Evidence (15): 2558–2564.

2. Miller LG, Tang AW (2004). Treatment of uncomplicated urinary tract infections in an era of increasing antimicrobial resistance. Mayo Clinical Procedures, 79(8): 1048–1054.