Sulfa Allergy

Antibiotics that contain a chemical called sulfonamides can trigger a reaction in individuals who have a sulfa allergy. Sulfa drugs are also known as sulfonamides, which include antibiotics and other types of medications, but allergy happens mostly with antibiotics. Sulfa allergy is an immunologically mediated hypersensitivity reaction. Your family doctor plays a critical role in reporting and documenting the allergic reactions properly. Some of the common sulfa-containing antibiotics that may cause undesirable allergic reactions include:

  • Sulfacetamide- Eye drops
  • Sulfamethoxazole-trimethoprim- Used to treat bacterial infections
  • Sulfasalazine- Used to treat inflammatory arthritis
  • Sulfadiazine- Used to treat bacterial infections
  • Sulfafurazole- Eliminates bacteria from the body

Causes of Sulfa Allergy

A sulfa allergy takes place when your immune system identifies the drug as a dangerous substance. Thus, your body develops antibodies specific to the drug and attack against it.

The presence of ‘sulfonamide’ in certain antimicrobial drugs can give rise to negative response when an individual has a sulfa allergy.

Such an allergic response takes place due to differences in the molecular structure between types of sulfonamides.

Chemically, sulfonamide antibiotics are different from other sulfonamides non-antibiotics because they have an ‘arylamine’ group. This arylamine group is associated with hypersensitivity and allergies.

A cross-reactivity between arylamine sulfonamides is common and thus, its use must be avoided in individuals who are sensitive to it.

Sulfa Allergy Symptoms

One may not experience allergic reactions the first time a sulfa-containing drug is taken, but your body could produce antibiotics against it. As a result, when you take a sulfa-containing drug the next time, your immune system may see it as a foreign substance and defend against it. Because of this, your body releases chemicals and you may develop symptoms.

Skin Reactions:

Allergic reactions caused by sulfa drugs can be commonly seen on the skin. These reactions on the skin can range from a simple rash to a life-threatening condition. Symptoms of sulfa-containing drugs on the skin include:

  • Hives
  • Itchy skin
  • Photosensitivity
  • Toxic epidermal necrolysis- A rare, but serious disorder of the skin and mucous membranes
  • Stevens-Johnson syndrome- A serious skin disorder in which, the skin turns red and blisters appear on the skin.

Initially, if the skin rashes go unnoticed and the drugs are not withheld, it may cause a serious health problem.

Respiratory System:

Sulfa-containing drugs may also have a negative impact on the respiratory system. Symptoms include:

  • Worsening of asthma
  • Wheezing
  • Congestion
  • Bronchoconstriction


Anaphylaxis is a life-threatening and severe allergic reaction. Such a case requires immediate medical attention. Symptoms include:

  • Low blood pressure
  • Heart Palpitation or rapid heart rate
  • Lightheadedness
  • Dizziness
  • Confusion

Other Symptoms:

  • Sulfa-medication may cause inflammation of the liver in individuals who are sensitive to sulfa
  • It can also damage the blood cells and cause kidney injury

Sulfa Allergy Diagnosis & Tests

It is important to quickly diagnose the condition and start with the treatment. Diagnosis relies on a careful history and physical examination.

History of Symptoms:

Your allergist may ask you details regarding the drug, such as:

  • Name of the drugs taken
  • Your doctor’s prescription
  • The time when the drug was taken
  • What symptoms were noticed first
  • When did the symptoms appear?
  • If any other multivitamin or herbal medications are taken

Your allergist may also ask you about other drug allergies and a family history of allergies.

All this investigation will give him a clear picture about your health status and drug allergy.

Besides this, there are no tests available that can be used to identify sulfa allergy.

Risk Factors

  • Individuals with a history of drug allergy are at a greater risk of sulfa allergy
  • Individuals with a family history of sulfa allergy
  • People with a poor immune system, for example- patients with HIV
  • Prolonged exposure to a drug or intake of high doses of a drug
  • Cross-sensitization

Treatment of Sulfa Allergy

  • Completely avoiding sulfa-containing medication is the best way to protect yourself against sulfa allergy
  • To treat the symptoms of sulfa allergy, such as hives, itching, redness and rash, your doctor may prescribe corticosteroids or antihistamines
  • Bronchodilator may also be advised if respiratory symptoms persist
  • Desensitization is a procedure, which your doctor may recommend if there is no sulfa-free alternative available. During this procedure, a low dose of the sulfa-containing drug is introduced to a point where the dose is effective and well tolerated. This process is monitored for allergic reactions
  • Stevens-Johnson syndrome and anaphylaxis are life-threatening conditions that require immediate medical attention and treatment. Antibiotics, corticosteroids and intravenous immunoglobulins are the different modes of treatment.


  • Inform all your healthcare providers about your sulfa allergy and the symptoms you experienced
  • Make a list of all the sulfa-containing drugs, which you need to avoid
  • Ask your doctor about the safe alternatives to sulfa-containing drugs
  • Carry an epinephrine syringe if you have had a severe anaphylactic reaction to sulfa drugs (1, 2, 3, 4)

List of Drugs to Avoid

Below mentioned are drugs that individuals sensitive to sulfa must avoid:

  • Sulfonamide antimicrobials are drugs used to treat microbial infections. Individuals with sulfa allergy must avoid sulfonamide drugs. These drugs are categorized by their common prefix ‘sulfa’.

Common sulfonamides include:

  1. Sulfadiazine
  2. Sulfacetamide
  3. Sulfasalazine
  • Diuretics are drugs that increase the production of urine. Loop diuretics and carbonic anhydrase inhibitors are two classes of diuretics that may cause cross-reactive sulfa allergy.
  • Sulfonylureas are drugs that increase the production of insulin and help in the management of diabetes. These drugs may trigger a cross-reactive allergy in people who are sensitive to sulfa drugs.
  • Some anti-inflammatory drugs contain a compound, which is similar to sulfonamide. Very little chances exist that these drugs may cause allergic reactions in individuals with sulfa allergy.

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