Active Ingredient

Sulfamethoxazole

Sulfamethoxazole is an antibiotic used to treat a variety of bacterial infections. It belongs to a class of drugs known as sulfonamides.

This medication is often prescribed for infections where bacteria are the cause, helping to clear up the infection and prevent its spread.

Written By Douglas C. Goldberg, MD

Reviewed By Philip Schein, MD

Last Updated 28 Nov 2025

Sulfamethoxazole Uses

Sulfamethoxazole is commonly used to treat bacterial infections in different parts of the body.

Urinary tract infections
Respiratory tract infections
Ear infections
Traveler’s diarrhea
Certain types of pneumonia

How Sulfamethoxazole Works

Sulfamethoxazole works by stopping the growth of bacteria. It interferes with the production of folic acid, a nutrient that bacteria need to multiply.

By blocking this process, the medication helps to eliminate the bacterial infection from the body.

This action makes it effective against a broad range of bacteria.

Common side effects of Sulfamethoxazole

Not everyone experiences side effects with Sulfamethoxazole, and many are mild and temporary.

Nausea
Vomiting
Loss of appetite
Rash
Dizziness
Headache
Fatigue

If you experience serious or persistent side effects, contact your doctor.

Take this medication with a full glass of water to prevent kidney stones.
Avoid excessive sun exposure, as Sulfamethoxazole can increase sun sensitivity.
Inform your doctor if you have a history of kidney or liver disease.
Do not mix with alcohol, as it may worsen certain side effects.
Seek medical attention if you develop a rash or difficulty breathing.

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

Frequently Asked Questions

How quickly does Sulfamethoxazole start working?

Sulfamethoxazole may start to improve symptoms within a few days, but it’s important to complete the full course as prescribed.

Can I take Sulfamethoxazole with other medications?

Inform your doctor about all medications you are taking, as Sulfamethoxazole can interact with other drugs.

Is it safe to drink alcohol while taking Sulfamethoxazole?

It is advisable to avoid alcohol as it can increase the risk of side effects such as nausea and dizziness.

What should I do if I miss a dose of Sulfamethoxazole?

If you miss a dose, take it as soon as you remember unless it is almost time for your next dose. Do not double up to make up for the missed dose.

Can Sulfamethoxazole cause an allergic reaction?

Yes, some people may experience an allergic reaction. Seek immediate medical attention if you notice symptoms like rash, itching, or difficulty breathing.