Sulfonamide: Mechanism of Action & Uses

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  • 0:03 Sulfonamides
  • 1:25 Sulfonamide Mechanism…
  • 2:32 Sulfonamide Uses
  • 3:50 Lesson Summary
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Lesson Transcript
Instructor: Alexandra Unfried

Alexandra earned her master's degree in nursing education and is currently a hospital supervisor/administrator.

Sulfonamides are also known as sulfa drugs. They are used as a type of antibiotic but can be used for other medical conditions as well. This lesson will discuss the mechanism of action and uses of sulfonamides.


Tiffany is a thirty year old who has been having painful urination. She is at her doctor's office describing her symptoms and is being prescribed a sulfonamide antibiotic medication for a urinary tract infection.

Sulfonamides, or sulfa drugs, are antibiotics that treat infections caused by bacteria. It's a synthetic drug, meaning that it is manufactured and is not naturally occurring. Sulfonamides are considered broad spectrum antibiotics. This means that they are able to treat a large variety of bacteria that cause disease.

Some diuretics, which are medications that increase the output of water and salt from the body, also have sulfa in them. An allergy to a sulfa-containing antibiotic doesn't necessarily mean that there's going to be an allergy to a diuretic that contains sulfa. This is because the two types of medication have different chemical make-ups. However, they should still be taken with caution and under the direction of a doctor.

Tiffany doesn't have an allergy to sulfa, so the sulfonamide antibiotic she is prescribed should be fine. Before she starts taking the medication the doctor wants to do a test called a urine culture to see what type of bacteria has caused her urinary tract infection. Since a sulfonamide is a broad spectrum antibiotic, it should be successful in treating the infection. However, if the antibiotic does not help, the results from the urine culture will help in deciding what type of antibiotic will work.

Sulfonamide Mechanism of Action

Folic acid is a vitamin that helps make DNA and red blood cells. A person has to ingest folic acid through their diet or supplements because the body cannot make it. On the other hand, bacteria can make their own folic acid which it uses to multiply and grow more bacteria. A sulfonamide interferes with the ability of bacteria to use folic acid to grow by stopping the metabolic process. Therefore, the bacteria are unable to reproduce.

Sulfonamide is considered a bacteriostatic because it's able to stop bacteria growth, but it isn't able to kill the bacteria. The white blood cells in the body are usually able to do that. Sometimes a different type of antibiotic is used along with a sulfonamide called trimethoprim. Trimethoprim is a bactericidal because it's able to kill the bacteria. The combination of the medications stops bacteria from multiplying and destroys them as well.

After two days of taking a sulfonamide antibiotic Tiffany is not feeling much better. Her doctor adds a trimethoprim antibiotic to help reduce the infection and promote healing. She's still waiting on the results of her urine culture which can take several days to result.

Sulfonamide Uses

One use of sulfonamides is to treat bacterial infections. Sulfonamide antibiotics may be prescribed for infections including:

  • Urinary tract infections
  • Pneumonia
  • Ear infections
  • Diarrhea
  • Bronchitis
  • Bacterial meningitis
  • Eye infections
  • Severe burns

Sulfonamides are also used to treat other medical conditions that include:

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