Sulfonamides, sometimes called sulfa drugs, are medicines that prevent the growth of bacteria in the body. The sulfonamides have largely been replaced by the antibiotics which generally are safer and more effective.


Sulfonamides are used to treat many kinds of infections caused by bacteria and certain other microorganisms. Physicians may prescribe these drugs to treat urinary tract infections, ear infections, frequent or long lasting bronchitis , bacterial meningitis , certain eye infections, Pneumocystis carinii pneumonia , traveler's diarrhea , and a number of other kinds of infections. These drugs will not work for colds, flu, and other infections caused by viruses.


Although there were many sulfonamides, relatively few are in use as of 2004:

  • Sulfisoxazole (Gantrisin) is used to treat urinary tract infections. In combination with erythromycin, sulfisoxazole may be used to treat ear infections in children.
  • Trimethoprim/sulfamethoxazole (Bactrim, Septra) is a combination of two sulfonamides used together. The combination is more effective than giving either drug alone in a larger dose. The combination is commonly used to treat urinary tract infections and other infections that cannot be treated with antibiotics.
  • Sulfadiazine may be used to protect people with rheumatic fever from infections. It is used to treat toxoplasmosis . An ointment containing silver sulfadiazine is widely used for treatment of burns.
  • Sulfasalazine (Azulfadine) is used to treat infections of the colon and intestine.

General use

The most common use for sulfonamides in adults is treatment of urinary tract infections. In children, sulfonamides have more limited use. Sulfisoxazole may be used for prophylaxis of ear infections and prevention of meningococcal infections. Sulfasakazube is used to treat children over the age of two years with ulcerative colitis.


Sulfonamides should never be used in infants under the age of two months. They should also be used with extreme care in patients with liver problems, kidney problems, and some types of anemia.

Side effects

Although such side effects are rare, some people have severe and life-threatening reactions to sulfonamides. These include sudden, severe liver damage; serious blood problems; breakdown of the outer layer of the skin; and a condition called Stevens-Johnson syndrome, in which people get blisters around the mouth, eyes, or anus. People should call a physician immediately if any of the following signs of a dangerous reaction occur:

  • skin rash or reddish or purplish spots on the skin
  • other skin problems, such as blistering or peeling
  • fever
  • sore throat
  • cough
  • shortness of breath
  • joint pain
  • pale skin
  • yellow skin or eyes

This medicine may cause dizziness . Sulfonamides may also cause blood problems that can interfere with healing and lead to additional infections. This medicine may increase sensitivity to sunlight. Even brief exposure to sun can cause severe sunburn or rash. While being treated with this medicine, people should avoid being in direct sunlight. Very rarely, systemic sulfonamides may even cause kidney stones.

The most serious adverse effects of sulfonamides cannot be predicted. Some steps can minimize some of the less severe adverse effects. Because sulfonamides are not very soluble, they should always be taken with a full glass of water. Moreover, sulfonamides increase sensitivity to sunlight and increase the risk of sunburn. People taking sulfonamides by mouth should avoid direct sunlight and stay covered up. They should not rely on sunscreens . This risk does not apply, however, to people using sulfonamide eye or ear drops. Oral sulfonamides should always be taken in evenly spaced doses to maintain a steady blood level throughout the day.


Sulfonamides may interact with a large number of other medicines. When interaction occurs, the effects of one or both of the drugs may change or the risk of side effects may be greater. People who take sulfonamides should let their physician know all other medicines they are taking. Among the drugs that may interact with sulfonamides are:

  • acetaminophen (Tylenol)
  • medicine for overactive thyroid
  • other medicines used to treat infections
  • birth control pills
  • medicines for diabetes, such as glyburide (Micronase)
  • anticoagulants, such as warfarin (Coumadin)
  • amantadine (Symmetrel)
  • water pills (diuretics) such as hydrochlorothiazide (HCTZ, HydroDIURIL)
  • the anticancer drug methotrexate (Rheumatrex)
  • antiseizure medicines such as valproic acid (Depakote, Depakene)

The list above does not include every drug that may interact with sulfonamides but is limited to drugs that might be used in treatment of children and adolescents. Parents should be sure to check with a physician or pharmacist before combining sulfonamides with any other prescription or nonprescription (over-the-counter) medicine.

Parental concerns

Parents giving their children eye or ear drops should be sure they know the proper way to administer these drops. Parents should review the technique with a physician or nurse to be sure the medication is given properly. If children are taking sulfonamides by mouth, parents should be sure that the children are drinking a full glass of water with each dose. Because some of the adverse effects of sulfonamides may be very serious, parents should report any suspicious symptoms to their physician promptly.

See also Cystitis ; Penicillins ; Tetracyclines .



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Nancy Ross-Flanigan Samuel Uretsky, PharmD

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