Drug Allergy

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

It is important to recognize the symptoms of a drug allergy, because they can be life-threatening. Death from an allergic reaction to a medication is extremely rare, however.

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 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, fewer than 10% of adverse drug reactions are allergic. Other causes of adverse reactions are interactions between two or more drugs, inability to break the drug down completely in the body (as occurs with liver or kidney damage), overdose, and irritating side effects such as nausea, vomiting, or diarrhea. If you have experienced a nonallergic drug reaction, it is important to describe it as such to medical personnel-not as an allergy. If you don’t know just describe the reaction the best way that you can.

An allergic reaction is caused by the body’simmune system overreacting 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 cause the symptoms of the reaction.
  • The most common triggers of drug allergies are the following:
    • Antibiotics such as penicillin, sulfa drugs, and tetracycline
    • Painkillers (called analgesics) such as codeine, morphine, nonsteroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen or indomethacin), and aspirin
    • Antiseizure medications such as phenytoin (Dilantin) or carbamazepine(Tegretol)
    • Contrast dye agents used in CAT scans
  • Risk factors for drug allergies include the following:
    • Frequent exposure to the drug
    • Large doses of the drug
    • Drug given by injection rather than pill
    • Family tendency to develop allergies andasthma
    • Certain food allergies such as to eggs, soybeans, or shellfish

Drug Allergy Symptoms
Drug allergies may cause many different types of symptoms depending on the drug and the degree of exposure to the drug (how often you have taken it). These are the most common reactions:

  • Skin reactions:
    • A measles-like rash
    • Hives-Slightly red, itchy, and raised swellings on the skin, which have an irregular shape
    • Photoallergy-Sensitivity to sunlight, an itchy and scaly rash that occurs following sun exposure
    • Erythema multiforme-Red, raised and itchy patches on the skin that sometimes look like bull’s-eye targets and which may occur together 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 theallergen, allergic reactions to drugs tend to occur days or weeks after the first dose of the drug.
  • 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. Characteristics of anaphylaxis (sometimes referred to as anaphylactic shock) include:
  • Skin reaction-Hives, redness/flushing, sense of warmth, itching
  • Difficulty breathing-Chest tightness, wheezing, throat tightness
  • Fainting-Light-headedness 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 four hours of the first dose of the drug. Most occur within one hour of taking the drug, and many occur within minutes or even seconds.

allergy-testing1In order to determine if you have an allergy to a specific drug, your doctor may ask you to describe your symptoms in detail. A physical examination may also be performed to identify if other health problems may be causing the symptoms.  The following tests may also be recommended to check for drug allergy;

Skin Test   The skin on the forearm or back is pricked and a small drop of the purified allergen is injected into the body.

If you are allergic to the drug, there will be a raised red bump in the injected area. Depending on the severity and type of drug allergy you may be suspected to have, allergy testing may be preferrably performed in a hospital setting in case of a severe allergic reaction to the testing dose itself.

Blood Test     A blood sample is obtained and then analyzed in the laboratory. This test helps to study the response of the immune system to the suspected drug. It measures the levels of specific antibodies in the blood.

In case these tests are not helpful in determining a drug allergy, your doctor may recommend an intradermall challenge. Because of the risk of a severe allergic response to the injection, it is preferrable to perform the intradermal challenge in a hospital setting where emergency treatment for anaphylactic shock or other severe allergy symptoms may result from the test. The advantage of the test is that identifying the drug allergy can also help in treating it.

In case an allergy is still unconfirmed, your doctor may order additional tests in order to check for other medical conditions.

treatment-icon4Generally, treatment of a drug allergy falls into three categories:

  • Mild allergy (localized hives and itching
    • Treatment is aimed at caring for the symptoms and stopping the reaction caused by the drug
    • Medications prescribed may include antihistamines, such as diphenhydramine (Benadryl)
    • You may be advised to stop taking the medication that caused the allergy.
  • Moderately severe allergy (all-over hives and itching)
    • Treatment is aimed at caring for the symptoms and stopping the reaction.
    • Usually the offending medication is stopped.
    • Medications prescribed may include antihistamines such as diphenhydramine (Benadryl)), oral steroids (prednisone), or histamine blockers such as cimetidine (Tagamet),famotidine (Pepcid), or ranitidine (Zantac).
  • Severe allergy(shortness of breath, throat tightness, faintness, severe hives, involvement of many organ systems)
    • Treatment includes strong medications to quickly reverse the dangerous chain of events.
    • The offending medication is stopped immediately.
    • Medications prescribed may include antihistamines such as diphenhydramine (Benadryl), oral or IV steroids such as prednisone ormethylprednisolone (Solu-Medrol), or histamine blockers such as cimetidine (Tagamet), famotidine (Pepcid), or ranitidine (Zantac).
    • Depending on the severity of other symptoms, other medications may be used including epinephrine (also called adrenaline), which is inhaled, given by IV, or injected under the skin.
    • If your reaction is severe, you may need to be admitted to the hospital for continued therapy and observation.