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Allergic Reaction to Medication

What Is an Allergic Reaction?

An allergic reaction is a response of the immune system to a trigger, known as an allergen. The immune system is designed to fight harmful substances. But sometimes the system can overreact causing allergy symptoms. A serious allergic reaction is known as anaphylaxis.

Medicines are a common cause of allergic reactions. Allergic reactions may also result from pollen, food, pets, insect stings, and other causes. Depending on the body’s response, an allergic reaction may be mild or severe. In most cases, allergic reactions are mild and can be treated with over-the-counter medications.

Severe allergic reactions can be life-threatening and need immediate medical treatment. Families should know the symptoms of an allergic reaction and have an action plan for emergencies. It is important to avoid what caused the allergic reaction to prevent another reaction in the future.

Symptoms of an Allergic Reaction

Mild Allergic Reaction Severe Allergic Reaction
Runny or stuffy nose Swelling of mouth, tongue, lips, throat, or eyes
Sneezing Low blood pressure
Itching Dizziness or fainting
Watery eyes Trouble swallowing or breathing
Skin redness or rash Nausea or vomiting

Common Questions About Drug Allergies

  1. Any type of medicine can cause a reaction. However, some medicines have a higher risk of drug allergy. These include:

    • Antibiotics
    • Pain relivers
    • Anti-seizure drugs
    • Chemotherapy drugs
    • Autoimmune disease drugs
  2. The most common symptoms of a drug allergy are rash, hives, itching, wheezing, or swelling. A more severe allergic reaction may occur, called anaphylaxis. Symptoms of anaphylaxis include facial swelling, throat swelling, trouble swallowing, trouble breathing, nausea or vomiting, low blood pressure, and dizziness or fainting.

  3. Anaphylaxis can sometimes cause the body to go into shock. This results in a lack of blood flow, and cells cannot get the oxygen they need. Anaphylactic shock can be fatal if the person does not receive immediate medical treatment.

  4. Most allergic reactions occur within hours of taking the drug. But in more rare cases, allergic reactions can occur later. Sometimes it can be hard to identify the cause of a reaction. The care team may look at factors such as the timing of the reaction, whether the drug is known to cause a reaction, what happened when the drug was stopped or taken again, and whether there are other possible reasons for the symptoms.

  5. A person may be at higher risk for a drug allergy based on certain factors such as:

    • Genetic factors; the presence or absence of certain genes can influence a person’s response to some medicines (pharmacogenetics)
    • History of allergies to other drugs, foods, or seasonal allergies; this can increase the risk of an allergic reaction
    • Age; drug allergies are more common in young or middle-aged individuals
    • Gender; drug allergies are more common in women
    • Infections or medical conditions, such as HIV or asthma; this can increase the risk of an allergic reaction
  6. Yes, it is possible for an allergic reaction to develop at any time. The timing of when an allergic reaction occurs is different for each person. Some may experience a reaction after the first dose of a drug. Other people may experience a reaction after taking the drug multiple times.

    In addition, the first time you a take a drug, you may have no allergic reaction. This is because your body is processing the drug and preparing its response. Your body identifies the drug as a harmful invader and develops a substance called an antibody. Later, when you take the drug again, the antibody senses the drug and tells your body to fight which leads to the allergic reaction symptoms.

  7. Yes, drug allergies can change over time. For example, many people who are allergic to penicillin eventually outgrow this drug allergy. A doctor or pharmacist can answer questions about drug allergy status and whether this might change. A patient with a previous history of drug allergy should be evaluated by an allergist or immunologist before using the medicine again.

Talking with Your Pharmacist About Drug Allergies

Pharmacists are trained to educate patients about drug allergies.

  • Pharmacists can help patients and families identify drug allergies by asking questions such as:
    • When did your reaction occur?
    • Have you had any recent drug changes?
    • What were your symptoms?
    • Does anything make you feel better or worse?
  • Pharmacists can help prevent drug-related allergic reactions. Families should make sure that a patient’s medication profile is up to date and includes all medicines and drug allergies. The pharmacist can make sure that a patient does not receive these specific drugs in the future. The pharmacist can also help families know if a related drug might cause a similar reaction.
  • Pharmacists can help treat your drug allergies by being a part of the care team and offering treatment recommendations. This may include stopping the drug, using a different dose or form of the drug, or using additional drugs to relieve allergy symptoms.

Steps to Handle Severe Allergic Reactions

It is essential to prepare and have an action plan in place to manage a severe allergic reaction. A severe allergic reaction needs urgent medical care as soon as possible. Do not wait to see if an allergic reaction improves or worsens. Call 911 immediately. A severe allergic reaction can lead to death.

Steps to take when a severe allergic reaction occurs:

  1. Call 911. DO NOT wait to see if symptoms improve.
  2. Give epinephrine, if available.
  3. Ensure clothes are loose to help breathing.
  4. Try to remain calm.
  5. Do not let the person eat or drink to prevent choking.
  6. If the person has problems breathing, is wheezing, or has hives, keep in an upright position.
  7. If the person is flushed, pale, or has a weak pulse, position lying down flat with feet elevated. If vomiting occurs, turn on side to prevent choking.
  8. Monitor pulse, breathing, and consciousness.
  9. If the person has no pulse, is not breathing, and is not conscious, begin CPR until help arrives (100-120 compressions per minute)

After a severe allergic reaction, symptoms can return. Patients may need medical care and monitoring for a period of time to make sure that the reaction has fully resolved.

SAFE Guide for Allergic Emergencies

The following guide can help during and after an allergic emergency:

S Seek immediate medical help.
A — Identify the allergen. What may have caused the reaction?
F Follow up with a specialist. An allergist or immunologist is a doctor who specializes in allergies.
E — Carry epinephrine for emergencies.

Allergic Reactions: Tips for Families

  • Make an action plan, and let others know. An action plan lets other people know about a patient’s specific allergies, current medications, action steps to take, and emergency contact numbers. Be sure to inform others at the patient’s school, work, or other places the patient spends time.
    • Download a sample action plan from the American Academy of Allergy, Asthma & Immunology
  • Wear medical identification. Patients at risk for severe allergic reactions should wear an emergency medical identification necklace or bracelet. This can help patients quickly receive medical care in the event of an emergency.
  • Have emergency supplies. If epinephrine is appropriate, keep it with you or your child at all times in case of a medical emergency. With this in mind, teach family and friends how to administer the epinephrine in the event that a reaction occurs.
  • Learn CPR. To learn CPR, visit the American Heart Association or American Red Cross websites to find a CPR training session near you.

Find More Information on Allergic Reactions


Reviewed: December 2019