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Drug Allergy


Allergic reaction is an uncommon and unwanted side effect of medication.

Several different types of allergic reactions can occur. Reactions to drugs range from a mild localized rash to serious effects on vital systems. The allergic response can affect many organ systems, but the skin is the most frequently involved.

It is important to recognize the symptoms of drug allergies, because they can be life threatening. However, death from an allergic reaction to a medication is rare.

An allergic reaction does not often happen the first time you take a medication. A reaction is much more likely to occur the next time you take that medication. If you have a reaction for the first time, you probably were exposed to the medication before without being aware of it.

Not all adverse reactions to drugs are allergies. In fact, less than 10 percent of adverse drug reactions are allergies. Other causes of adverse reactions are interactions between 2 or more drugs, inability to break the drug down completely in the body (as in liver or kidney damage), overdose, and unwanted side effects such as nausea, vomiting, or diarrhea.

Signs and symptoms

Drug allergies may cause many different types of symptoms depending on the drug and how often you have taken it. These are the most common reactions:

  • Skin
    • Measles-like rash
    • Hives – Slightly red and raised swellings on the skin, irregular in shape, itchy
    • Photoallergy – Sensitivity to sunlight, an itchy and scaly rash when you go out in the sun
    • Erythema multiforme – Red, raised and itchy, may look like bull’s-eye targets lesions, sometimes associated with swelling of the face or tongue
  • Fever
  • Muscle and joint aches
  • Lymph node swelling
  • Inflammation of the kidney
  • Unlike most allergic reactions, which occur fairly quickly after exposure to the allergen, allergic reactions to drugs tend to occur days or weeks after the first dose.
  • Anaphylaxis or anaphylactic reaction – This is a serious allergic reaction that can be life threatening. A person with anaphylaxis must be treated in a hospital emergency department.
    • Skin reaction – Hives, redness/flushing, sense of warmth or feeling itching
    • Difficulty in breathing – Chest tightness, wheezing, throat tightness
    • Fainting – Light-headness or loss of consciousness due to drastic decrease in blood pressure (“shock”)
    • Rapid or irregular heart beat
    • Swelling of face, tongue, lips, throat, joints, hands, or feet
  • Almost all anaphylactic reactions occur within 4 hours after the first dose. Most occur within 1 hour of taking the drug, and many occur within minutes or even seconds.

Common Cause of Drug Allergy

An allergic reaction occurs when the body immune system overreact to the drug, which is viewed as a chemical “invader,” or antigen. This overreaction is often called a hypersensitivity reaction.

The body produces antibodies to the antigen and stores the antibodies on special cells.

  • The antibody in an allergic reaction is called immunoglobulin E or IgE.
  • When the body is exposed to the drug again, the antibodies signal the cells to release chemicals called “mediators.” Histamine is an example of a mediator.
  • The effects of these mediators on organs and other cells manifest as symptoms as a result of the reaction.

The most common triggers of drug allergies are the following:

  • Painkillers (called analgesics) such as codeine, morphine, nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen or indomethacin), and aspirin
  • Antibiotics such as penicillin, sulfa drugs, and tetracycline
  • Antiseizure medications such as phenytoin (Dilantin) or carbamazepine (Tegretol)

Risk Factors

Risk factors for drug allergies

  • Familial tendency to develop drug allergy
  • Multiple drugs taken at the same time (drug-drug interaction)
  • The kidney or liver not functioning well
  • Diseases that affects immune system such as systemic lupus erythematosis or HIV


Treatment for drug allergies includes understanding of what to do if you have a severe allergic reaction, avoiding the medicine that causes the allergy, and using medicines such as antihistamines for mild symptoms.

If you suspect having allergy shortly after taking a medication or various medications, see your doctor. You can take an antihistamine such as chlorpheniramine malaete (piriton or others) to relieve itching and calm a rash. More severe reactions may require treatment with oral or injected corticosteroids. Anaphylaxis is an emergency situation requiring an immediate epinephrine injection and hospital care to maintain blood pressure and support breathing.


  • There is no known way to prevent drug allergies. You can reduce your risk by taking as few medications as possible. The more exposure your body has to medications, the greater is the likelihood of a drug allergy.
  • Always tell any new health care provider you see about your allergies and the types of reactions you have had.
  • Do not take any drug that you have reacted to in the past. Once you have a reaction to a drug, your risk of having a more severe reaction the next time increases dramatically.
  • Consider wearing a medical alert ID bracelet or necklace. These devices are worn on the wrist or neck and can alert medical personnel and others about the risk for an allergic reaction.
  • Adults might carry a card with pertinent medical information in a wallet or purse. Tell your health care provider about any adverse reactions to medications in the past before he or she prescribes medications to you.
  • Tell your health care provider about any medications, prescription or over-the-counter drugs that you are taking.
Last Reviewed : 25 April 2012
Writer : Ali bin Puteh
Reviewer : Datin Dr. Asmah Johar