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By Hans P. Schlecht, MD, MSc, Assistant Professor of Medicine, Department of Medicine, Division of Infectious Diseases & HIV Medicine, Drexel University College of Medicine
Christopher Bruno, MD, Assistant Professor of Medicine, Division of infectious Diseases & HIV Medicine, Drexel University College of Medicine

Sulfonamides are a class of antibiotics that are effective against many gram-positive and gram-negative bacteria. Some sulfonamides are used topically to treat burns and skin, vaginal, and eye infections.

Sulfonamides include the following:

  • Mafenide

  • Sulfacetamide

  • Sulfadiazine

  • Sulfamethizole

  • Sulfasalazine

  • Sulfisoxazole

  • Sulfamethoxazole (in combination with trimethoprim)

Sulfamethoxazole is available only in combination with trimethoprim (as 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 sulfasalazine: Inflammatory bowel disease

For sulfacetamide: Superficial eye infections

For mafenide: 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 women or fetuses 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, which may be severe enough to cause brain damage (kernicterus) in the fetus or newborn.

Sulfonamides should not be taken during breastfeeding.

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