Drug allergy

Disease Description (Causes and Symptoms)

• Definition: Drug allergy is an adverse reaction that occurs when an immune-mediated (hypersensitivity) reaction is triggered by using a drug at a standard dose and through an appropriate route of administration. It includes both immediate (acute, IgE-mediated) and delayed (T-cell-mediated) reactions.
• Main causative drugs: Antibiotics (such as penicillins and sulfonamides), nonsteroidal anti-inflammatory drugs (NSAIDs), aspirin, anticonvulsants (such as carbamazepine), contrast media, anticancer drugs, and others.
• Pathophysiology summary: The drug or its metabolite acts as an antigen, triggering the production of specific antibodies (IgE) or a T-cell-mediated immune response → release of histamine and cytokines → symptoms involving the skin, respiratory system, blood vessels, and internal organs.
• Main symptoms: Rash (hives, erythema), itching, fever, swelling (of the face, pharynx, lips, and limbs), vomiting, nausea, diarrhea, joint pain, muscle pain, and enlarged lymph nodes. In severe cases, anaphylaxis (difficulty breathing, low blood pressure, decreased consciousness), damage to organs such as the blood, liver, and kidneys, or severe cutaneous reactions (SJS/TEN, DRESS) may occur.
• Time course: Immediate reactions occur within minutes to hours after administration, while delayed reactions appear within hours to weeks. The reaction may become more severe upon re-exposure.

Treatment Methods and Precautions

• Immediate treatment (stop all suspected drugs)
  • Mild symptoms (localized rash or itching): Stop the causative drug, use an antihistamine (oral H1), apply a topical moisturizer or steroid, etc.
  • Anaphylaxis: Immediately administer intramuscular epinephrine (adults: 0.3–0.5 mg, 1:1,000 dilution, into the lateral thigh), secure the airway, provide oxygen, administer large-volume fluids, and observe the patient in the hospital. Antihistamines and steroids are adjunctive treatments.
  • Serious allergic organ damage or severe cutaneous reactions (SJS/TEN, DRESS): Immediate hospitalization (intensive care or a burn specialty unit), discontinuation of the causative drug, and supportive treatment (fluids, electrolytes, infection control). Specialist immunotherapy (steroids, IVIG, cyclosporine, etc.) is determined according to the symptoms and available evidence.
• Diagnostic evaluation (performed alongside treatment)
  • Skin testing: Useful for some drugs, including penicillins (for confirming specific IgE).
  • Serum-specific IgE testing: An auxiliary test when an immediate reaction is suspected.
  • Patch testing: Used to evaluate delayed contact and skin reactions.
  • Drug provocation testing (challenge test): The gold standard for diagnosis, but contraindicated in patients with a history of severe reactions (SJS/TEN, DRESS, severe anaphylaxis, etc.). It must be performed by a specialist in a hospital setting.
• Drug re-administration and desensitization
  • When no alternative drug is available and use of the drug is essential, temporary tolerance may be induced through gradual desensitization under specialist supervision. Because it carries significant risks, it should be performed at a specialized center.
• Prevention and self-care
  • Record confirmed causative drugs in the electronic medical record, medical certificates, allergy cards, and medical alert devices (such as bracelets).
  • If there is a history of anaphylaxis, consider prescribing a disposable epinephrine auto-injector (EpiPen).
  • Always inform medical institutions of your allergy history and information about causative drugs when seeking care.
  • For suspected cross-reactions (e.g., penicillin–cephalosporin), consult a specialist to select a safe alternative.

Checklist Before an Outpatient Visit (Items to Bring and Sample Questions)

Items to bring

• A list of currently used medications (including prescription drugs, OTC drugs, herbal medicines, and nutritional supplements) or photos of medication packages
• Written records or photos (such as rash photographs) documenting the timing of past drug reactions, drug names, route of administration, dose, time of onset, symptoms, and treatment provided (including emergency department or hospitalization records)
• Results of previous allergy tests (skin tests, blood tests, and provocation tests), medical records, or medical certificates
• Notes on underlying conditions (asthma, heart disease, pregnancy, etc.) and current symptoms
  Examples of questions to answer yourself before asking the doctor during an outpatient visit
• After taking which drug did the symptoms begin? How many minutes, hours, or days after taking it did the symptoms appear?
• Did you have a problem when taking the same class of drug or a similar drug in the past?
• How severe were the symptoms, and did you receive emergency treatment (epinephrine administration, hospitalization, etc.)?
• Are there any warning signs currently present, such as difficulty breathing, fever, progressive skin damage, or decreased urination?

Examples of General Questions to Ask the Doctor

• How likely is it that this drug (or class of drugs) caused my symptoms?
• Do I need additional tests in my case (skin test, blood test, or drug provocation test)? What are the risks?
• What safe alternative drugs are available? What precautions should I take when undergoing surgery, anesthesia, or contrast media administration?
• If I have a history of anaphylaxis, do I need an EpiPen prescription? Could you explain how to use it?

Examples of Condition-Specific Questions

• Suspected penicillin allergy:
  • “A penicillin allergy is recorded in my medical history. Is it safe to confirm this with a skin test or provocation test? If the result is negative, can I use penicillin antibiotics?”
• Symptoms related to NSAIDs (aspirin):
  • “I experienced difficulty breathing, a runny nose, and hives when taking aspirin (or another NSAID). Do I need to avoid all NSAIDs? What pain relievers can I safely take?”