Sulfonamide: Definition, Function, Side Effects, Interactions and Presentations

They are drugs derived from sulfanilamide, a chemical that contains sulfur.

Most sulfonamides are antibiotics, but some are prescribed to treat ulcerative colitis.


Sulfonamide antibiotics work by stopping the production of dihydrofolic acid, a form of folic acid that bacteria and human cells use to make proteins.

What are the side effects of sulfonamides?

Sulfonamides can cause:

  • Dizziness.
  • Headache.
  • Lethargy.
  • Diarrhea.
  • Anorexia.
  • Nausea.
  • Vomiting
  • Serious skin rashes.

Sulfonamides should be discontinued at the first appearance of a rash before the rash becomes severe.

Serious rashes include:

Stevens-Johnson syndrome, which includes symptoms such as:


  • Aching joints.
  • Muscle pain.
  • Redness.
  • Blisters

Toxic epidermal necrolysis, which includes symptoms such as:

  • Difficulty in swallowing.
  • Redness.
  • Blisters of the skin.

They can also cause sun sensitivity that causes extensive burns after exposure to sunlight (photosensitivity).

Patients receiving sulfonamides should avoid excessive exposure to sunlight and should use sunscreen.

Other rare side effects include liver damage, low white blood cell count ( leukopenia ), low platelet count ( thrombocytopenia ), and anemia.

The formation of urinary crystals can damage the kidney and cause bleeding. Adequate hydration is needed to prevent the formation of urinary crystals.

What are examples of sulfonamides?

Examples of sulfonamides include:

  • Sulfametoxazol / trimetoprima (Bactrim, Bactrim DS, Septra, Septra DS).
  • Sulfasalazina (azulfidina, sulfazina).
  • Sulfisoxazol (Truxazol).

Many of these medications are available only in generic forms.


They can increase the anticoagulant effects of warfarin (Coumadin), possibly leading to abnormal bleeding.

Increased metabolism (breakdown and elimination) of cyclosporine by the liver caused by sulfonamides reduces the efficacy of cyclosporine and may increase renal damage caused by cyclosporine.

All sulfonamides can crystallize in the urine when the urine is acidic. Since methenamine (Hiprex, Urex, Mandelamine) causes acid urine, it should not be used with sulfonamides.

Blood levels of digoxin can increase digoxin (Lanoxin) and possibly lead to severe toxic effects.

Due to a reduction in folic acid, anemia can occur in people receiving sulfonamides in combination with Divalproex, valproic acid (Depakote, Depakote ER, Depakene, Depacon, Stavzor), methotrexate (Rheumatrex, Trexall), pyrimethamine, triamterene or trimetrexate.

Elevated potassium levels in the blood may occur when sulfamethoxazole/trimethoprim is combined with angiotensin-converting enzyme (ACE) inhibitors.


They are available in tablets, injections, and oral solutions.

Pregnancy and lactation

Sulfonamides can cause the bilirubin to move from the proteins in the baby’s blood. The displacement of bilirubin can cause jaundice and a dangerous condition called kernicterus in the baby.

For this reason, sulfamethoxazole/trimethoprim should not be used in the short term (late pregnancy) among women.

Nursing mothers should not use Sulfonamides (e.g., sulfamethoxazole/trimethoprim) because sulfamethoxazole is excreted in breast milk and can cause kernicterus.


They are a class of drugs from a chemical substance that contains sulfur (sulfanilamide).

Los ejemplos de sulfonamidas incluyen sulfametoxazol / trimetoprima (Bactrim, Bactrim DS, cotrimoxazol, Septra, Septra DS, Cotrim, SMZ-TMP, SMZ-TMP DS, Sulfatrim); sulfasalazina (azulfidina, sulfazina); y sulfisoxazol (Truxazol, Gantrisina).

Some of these medications are available only in generic forms. Side effects of sulfonamides may include dizziness, lethargy, diarrhea, nausea, vomiting, headache, severe skin rashes, and anorexia.

They are not recommended for women who are pregnant or breastfeeding. Side effects and drug interactions should be reviewed before taking this medication.