Sulfonamides: Types, Usage, Side Effects & More

By Zina Semenovskaya, MD
Medically reviewed checkmarkMedically reviewed
December 28, 2021

Sulfonamides were the first antibiotics discovered and used, and have been used by doctors since the 1930s.

Also referred to as sulfa drugs, sulfonamides are man-made antibiotics that are used to treat bacterial infections.

If you are struggling with a UTI, bronchitis, pneumonia, or have an eye or ear infection that requires an antibiotic, your health care provider may prescribe you sulfonamides. 

In this article, I’ll explain what sulfonamides are, how they work, and what conditions they’re used to treat.

I’ll list some common sulfa drugs, and talk about their side effects and dosage.

I’ll also provide some precautions about these antibiotics, and tell you when you should talk to a doctor.

What are Sulfonamides?

Sulfonamides are a class of broad-spectrum antibiotics, meaning they work against a wide range of bacteria. 

How do Sulfonamides Work?

Sulfonamides, or sulfa drugs, are a class of broad-spectrum antibiotics that act on a wide range of gram-positive and gram-negative bacteria.

Sulfa drugs do not kill bacteria, but instead work by inhibiting the bacteria from growing and multiplying, thus stopping the infection.

They do this by stopping bacteria from making folic acid, which is necessary for their growth.

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What are Sulfonamides Used to Treat?

Sulfonamides have been around since the 1930s and were some of the first effective antibiotics to be introduced into clinical medicine.

Unfortunately, bacterial resistance to sulfonamides is now common, making them less effective against the most common bacteria.

Urinary tract infections

If you have a urinary tract infection (UTI) that is known to be susceptible to sulfonamides, you may be prescribed these antibiotics by your doctor.

UTIs occur when bacteria from the skin or rectum enter the urethra and infect the urinary tract.

A UTI can infect any part of the urinary system, including your kidneys, bladder, or urethra 


Bronchitis is an infection of the lungs that causes the lining of your bronchial tubes to become inflamed.

While most cases of bronchitis are caused by a virus, it can sometimes also be caused by bacteria.

If you have persistent bronchitis, or other symptoms that lead your healthcare provider to suspect that it may be due to a bacterial infection, they may prescribe you antibacterial agents such as sulfonamides.

Eye infections

If you have a bacterial eye infection such as conjunctivitis, your doctor may prescribe you sulfonamides to treat it.

For eye infections, antibiotics are typically prescribed in the form of eye drops or ointment.

Bacterial meningitis 

Meningitis is a severe brain infection that can be viral or bacterial.

When it is caused by a bacteria called Listeria monocytogenes and the patient has an allergy to penicillin, sulfa drugs may be prescribed to treat meningitis. 


If you are diagnosed with pneumonia, this means the air sacs of one or both lungs have become inflamed and may also be full of liquid or pus, making it difficult to breathe.

Pneumonia is caused by bacteria, fungi, viruses, or chemical irritants.

When pneumonia is caused by a bacterial infection, your doctor may prescribe sulfonamide antibiotics to treat it.

Ear infections

Sulfonamides are used to treat bacterial ear infections, especially in children.

The medication is usually a combination of erythromycin and sulfafurazole, and has been proven to be highly effective, with significant improvement within a few days.


If you have an extensive second or third-degree burn, you may contract a bacterial infection.

Sulfa drugs can help treat these infections and may sometimes be used prophylactically, especially when applied in the form of a cream to the affected skin.

Common Sulfonamides


Gantrisin (acetyl sulfisoxazole pediatric suspension) (sulfisoxazole) is an antibacterial sulfonamide used to treat bladder infections, ear infections, and meningitis.

It is available in liquid form, which is especially useful for pediatric patients.

It is also available as an eye drop or ophthalmic ointment.


Sulfadiazine is usually prescribed in tablet form.

It is used to treat infections including urinary tract infections, ear infections and parasitic infections such as toxoplasmosis.

It can also help prevent rheumatic fever and meningitis.

Bactrim or Septra

Bactrim or Septra are two antibiotics (sulfamethoxazole and trimethoprim) that are usually prescribed together to treat common infections, including urinary tract infections and skin infections. 


Sulfasalazine delayed-release (Azulfidine EN-tabs) is used to treat a specific type of bowel disease called ulcerative colitis.

It can also be used for rheumatoid arthritis in adults and children when other medications have not worked effectively.

Sulfasalazine is an anti-inflammatory drug that works by reducing inflammation in the body.


Zonegran is primarily used as an epilepsy medication.

It is used to prevent and control seizures in adults in conjunction with other medicines. 

Side Effects of Sulfonamides

Sulfonamides may cause you to have adverse reactions that require medical attention.

Common side effects you may experience from taking sulfonamides include:

Less common side effects you might experience include:

  • Aching muscles and joints
  • Trouble swallowing
  • Sore throat 
  • Fever
  • Unusual bleeding or bruising
  • Yellow eyes or skin
  • Pale skin

In rare circumstances, you may experience any of the following:

  • Abdominal or stomach cramps, pain, or tenderness 
  • Blood in urine
  • Diarrhea that is watery or bloody
  • Changes in urination: urinating a lot, or not at all
  • Pain or burning when urinating
  • Dehydration
  • Mood changes
  • Lower back pain
  • Swelling of the front part of the neck

Always check with your healthcare professional if you have any of the above symptoms.

If you suspect you are having a serious allergic reaction or have overdosed, stop taking the medication immediately and call 9-1-1.

You can also report your symptoms to the FDA at 1-800-FDA-1088.

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Sulfonamides Precautions

Before taking sulfonamides, tell your doctor about all medical conditions you have, especially if you have any liver, kidney, or blood disorders.

Mention all prescription and non-prescription drugs that you are taking, including all herbal, nutritional, or dietary supplements.

Sulfa drugs should not be given to infants younger than two months old.

Tell your doctor if you are pregnant, planning on becoming pregnant, or are breastfeeding, as the drug can be passed through breast milk.

Sulfa drugs can cause a serious, even life-threatening, skin rash and make your skin extremely sensitive to the sun.

Avoid unnecessary sun exposure, and inform your healthcare provider immediately if you notice a rash or other unusual skin changes.

Always read all of the information on the prescription label and only take the medication as directed by your doctor or pharmacist.

Your dosage may change as your doctor monitors your body’s response to the medicine.

If you feel dizzy or nauseous, avoid driving or operating heavy machinery. 

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Frequently Asked Questions

What are examples of sulfonamides?
Sulfonamides include Gantrisin, Sulfadiazine, Bactrim or Septra, Azulfidine, and Zonegran.
Which drugs are sulfa drugs?
Sulfa drugs are broad-spectrum antibiotics that are used to treat a wide variety of bacterial infections. Sulfa drugs include Gantrisin, Sulfadiazine, Bactrim or Septra, Azulfidine, and Zonegran.
What are sulfonamides used for?
Sulfonamides inhibit the growth of harmful bacteria in the body. They are used to treat a variety of infections, including urinary tract infections, skin infections, lung infections, and other bacterial and parasitic infections.
What is the mechanism of action of sulfonamide?
Sulfonamides work by preventing bacteria from making folic acid, preventing their growth and reproduction.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.

Zina Semenovskaya, MD

Dr. Semenovskaya specializes in emergency medicine, and received her medical degree from Weill Cornell Medical College. She is currently the medical director at Remote Emergency Medicine Consulting, LLC and splits her time working clinically as an emergency medicine attending in California and Alaska. She is the first of our doctors to be fluent in Russian.

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