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 body’s response can affect many organ systems, but the skin is the 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 percent of adverse drug reactions are allergic. 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 irritating side effects such as nausea, vomiting, or diarrhea.

An allergic reaction is caused by the body's immune 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:
  • 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 for drug allergies
  • Frequent exposure to the drug

  • Large doses of the drug

  • Drug given by injection rather than pill

  • Family tendency to develop allergies and asthma

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, sometimes look like bull's-eye targets, sometimes 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 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.

• Skin reaction - Hives, redness/flushing, sense of warmth, itching

• Difficulty 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 of the first dose of the drug. Most occur within 1 hour of taking the drug, and many occur within minutes or even seconds.

Always contact the health care provider who prescribed the medication for advice.

• If the symptoms are mild, such as itching and localized hives, the provider may switch you to a different type of medication, recommend that you stop the medication, or, if appropriate, prescribe antihistamines to relieve your symptoms.

• If you cannot reach this provider for advice quickly, play it safe and go to a hospital emergency department.

• If you are having any "systemic" symptoms such as fever or vomiting, you should stop taking the medication and be seen immediately by a medical professional.

• If you are having difficulty breathing, your throat is swelling, or you are feeling faint, you may be having an anaphylactic reaction. Go immediately to a hospital emergency department. Do not attempt to drive yourself. If no one is available to drive you right away, call 911 for an ambulance. While waiting for the ambulance, start self-treatment.

Generally a drug allergy is identified by signs and symptoms. Medical professionals are trained to recognize hives, swelling patterns, and rashes associated with allergic reactions.

You will be asked questions about your medical history and possible triggers of the reaction.

Blood tests and other tests are needed only under very unusual circumstances.

After getting advice from your health care provider, some mild allergic reactions may be treated at home.

|Self-Care at Home|

For hives or localized skin reactions, perform the following:

• Take cool showers or apply cool compresses.

• Wear light clothing that doesn't irritate your skin.

• Take it easy. Keep your activity level low.

• To relieve the itching, apply calamine lotion or take nonprescription antihistamines, such as diphenhydramine (Benadryl) or chlorpheniramine maleate (Chlor-Trimeton).

For more severe reactions, self-treatment is not recommended. Call your health care provider or 911, depending on the severity of your symptoms. If you have symptoms of anaphylaxis, here's what you can do while waiting for the ambulance:

• Try to stay calm.

• If you can identify the cause of the reaction, prevent further exposure.

• Take an antihistamine (1-2 tablets or capsules of diphenhydramine [Benadryl]) if you can swallow without difficulty.

• If you are wheezing or having difficulty breathing, use an inhaled bronchodilator such as albuterol (Proventil) or epinephrine (Primatene Mist) if one is available. These inhaled medications dilate the airway.

• If you are feeling lightheaded or faint, lie down and raise your legs higher than your head to help blood flow to your brain.

• If you have been given an epinephrine kit, inject yourself as you have been instructed. The kit provides a premeasured dose of epinephrine, a prescription drug that rapidly reverses the most serious symptoms.

• Bystanders should administer CPR to a person who becomes unconscious and stops breathing or does not have a pulse.

• If at all possible, you or your companion should be prepared to tell medical personnel what medications you take and any known allergies.

|Medical Treatment|

Generally, treatment of a drug allergy falls into 3 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 or methylprednisolone (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 or 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.

|Follow-up|

Follow up with your health care provider after an allergic reaction to a drug. At this follow-up appointment, he or she can evaluate your recovery from the reaction and adjust any medications.

If you do not respond to the treatment prescribed for your drug allergy, it is important that you see a medical professional for re-evaluation.

|Prevention|

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 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 a 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 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, that you are taking.

|Outlook|

Most people who have mild to moderately severe allergic reactions to a drug do very well. With treatment and stopping of the drug, most people will be much better within 48-72 hours.

Most people also do well after a severe drug allergy if they are evaluated promptly by a medical professional and treatment is started. Some reactions can be life threatening, including serum sickness and anaphylaxis. People who have these reactions generally need to be admitted to the hospital.

|Support Groups and Counseling|

Allergy and Asthma Network - Mothers of Asthmatics

Asthma and Allergy Foundation of America
1233 20th St. NW, Suite 402
Washington, DC 20036
(202) 466-7643

|Web Links|

American Academy of Allergy, Asthma and Immunology

National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health

National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health

Nemours Foundation – For information on allergies in children

drug allergy, allergen, allergic reaction, anaphylactic shock, anaphylaxis, antibodies, antibody, hypersensitivity, immune system, immunoglobulin E, IgE, serum sickness 

Author: Kevin Hanson, MD, Staff Physician, Department of Emergency Medicine, University of Arizona College of Medicine.

Coauthor(s): Samuel M Keim, MD, Program Director, Associate Professor, Department of Surgery, Division of Emergency Medicine, University of Arizona Health Sciences Center.

Editors: Patrick Taylor, MD, FAAEM, Medical Director, Department of Emergency Medicine, CHRISTUS St Frances Cabrini Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, ; James S Cohen, MD, Consulting Staff, James Cohen, PC.