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Brian J. Werth

, PharmD, University of Washington School of Pharmacy

Last full review/revision Jul 2020| Content last modified Jul 2020
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Sulfonamides are a class of antibiotics that are effective against many gram-positive bacteria and gram-negative bacteria. Some sulfonamides are applied directly to the skin (topically) to treat burns and skin, vaginal, and eye infections.

Sulfonamides include the following:

Sulfamethoxazole (SMX) is commonly used in combination with trimethoprim (TMP). The combination is called TMP/SMX.

Sulfonamides work by preventing bacteria from producing a form of folic acid they need to grow and multiply.




Common Uses

Some Side Effects









Urinary tract infections (except sulfasalazine, sulfacetamide, and mafenide)

For sulfanilamide: Inflammation of the vagina (vaginitis)

For sulfasalazine:Inflammatory bowel disease

For sulfacetamide: Superficial eye infections

For mafenide and sulfadiazine: Only topically for burns

For trimethoprim/sulfamethoxazole: Skin infections caused by susceptible bacteria that are resistant to other antibiotics, including methicillin-resistant Staphylococcus aureus (MRSA)

Nausea, vomiting, and diarrhea

Allergy (including rashes)

Crystals in urine (rare)

A decrease in white blood cell and platelet counts

Sensitivity to sunlight

Possibly increased tendency to bleed if used with warfarin

In people with G6PD deficiency (see table More About Some Causes of Anemia), the breakdown of red blood cells

G6PD = deficiency of glucose-6-phosphate dehydrogenase.

Use of Sulfonamides During Pregnancy and Breastfeeding

Sulfonamides should be used during pregnancy only when the benefits of treatment outweigh the risks. However, they should not be used when the due date is near because, taken at that time, they may cause jaundice in the newborn, which may be severe enough to cause brain damage (kernicterus) in the newborn. (See also Drug Use During Pregnancy.)

Sulfonamides should not be taken during breastfeeding. (See also Drug Use During Breastfeeding.)

Drugs Mentioned In This Article

Generic Name Select Brand Names
No US brand name
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