Drug Allergies

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What is a drug allergy?

A drug allergy is due to a specific and reproducible immune response to a particular medication.  Some drug allergies carry a risk of "allergic shock" or anaphylaxis if the medication is taken again.  There are other types of immune reactions that carry different risks.  Skin rashes are common in many types of drug allergies.

What is the difference between a drug allergy and other drug reactions?

Drug allergy is one type of severe adverse drug reactions.  These are dangerous reactions, and medication and related substances need to be avoided.  Intolerances are less severe and do not involve the immune system.  In these cases, although the effects are undesirable, they may be worth the benefit received by taking the medication.  Drug intolerance reactions may respond to dose reduction or taking a different but related medication.  These actions could be dangerous if you have a true drug allergy.

How common are drug allergies?

Only 5-10 percent of adverse drug reactions are drug allergies.

What causes drug allergies?

Acute or rapid drug allergies are generally due to allergic antibodies (IgEs) to the drug in question.  Interactions between the problem drug and allergic antibodies (IgE) cause the allergic reaction by releasing histamine and other inflammatory chemicals.  This cascade causes allergy symptoms that can range from uncomfortable to life threatening such as hives, swelling, trouble breathing, vomiting, or even anaphylaxis ("allergic shock") if the medication is taken again.

There are other types of immune reactions that work on different pathways and result in different reactions.

Which medications are most often associated with drug allergies?

Any medication can cause a drug allergy but some are more likely.  Drug allergies to antibiotics including penicillin and related medications are the most common.  Many people are allergic to aspirin and related drugs called NSAIDs (nonsteroidal anti-inflammatory drugs) such as ibuprofen or naproxen.  Anti-seizure medications can cause severe adverse drug reactions.   Always consult your doctor and pharmacist about potential drug allergies. 

What are the symptoms of drug allergies?

Rash is the most common symptom. The symptoms and severity of drug allergy reactions can vary from person to person and also depend on the specific medication(s) you are taking.  Always consult your doctor for a diagnosis.  Some common symptoms are listed below:

  • Rash including raised or flat skin color changes
  • Hives, or itchy, raised bumps
  • Swelling of the skin or mouth
  • Tightness in the throat or hoarse voice
  • Trouble breathing or wheezing

Severe reactions such as anaphylaxis are medical emergencies and are treated with epinephrine.  Call 911 for immediate medical assistance. 

Can I be allergic to a drug I have taken many times before?

Yes, repeatedly taking the same medication for limited periods of time actually increases the likelihood of a drug allergy.  For example, some people can develop drug allergies to antibiotics.

Can people outgrow drug allergies?

Drug allergies can change with time.  In fact, many, but not all people with a documented drug allergy to penicillin outgrow this allergy after 10 years.  Other drug allergies are considered life-long.  If you want to find out the status of a drug allergy, discuss this with your doctor.

How is a drug allergy diagnosed?

The most important tool to diagnose a drug allergy is a discussion with your doctor about the exact details of the reaction and a detailed physical exam.  If you are not able to see your doctor right away, take pictures of the rash or other problem.

Unfortunately, there are very few good tools to help us identify drug allergies and it can be difficult to identify which drug is responsible for a rash or other problem.  For some medications, skin tests or laboratory tests can be helpful.  Sometimes, a referral to a dermatologist is needed for a skin biopsy.  Other times a closely monitored drug challenge is needed to determine if an allergy is present.

Can I be tested for a penicillin allergy?

Luckily, there is an excellent test for penicillin allergy.  This is a skin test that first pricks the top layer of skin with the medication.  If this does not show a reaction, injections of the medication are then placed under the skin.  If no reaction occurs, then you are no longer allergic.  The reason that penicillin skin testing is an effective test is that all of the important metabolites have been identified.  This means that the penicillin skin test can correctly identify not only who is allergic to penicillin, but also who is not allergic.

What is a drug challenge?

Graded dose drug challenges are performed when drug allergy testing is unlikely to prove that you are not allergic to a medication.  In a monitored setting, increasing amounts of the medication in question are given by doctors and nurses skilled at recognizing and treating allergic reactions.

How does a drug challenge work?

We offer drug challenges in the inpatient and outpatient setting. The drug challenge is generally performed only if medically acceptable alternatives do not exist and only when any other concurrent health issue is under optimal control.

This is a >4 hour procedure involving the administration of a carefully monitored test dose in one or more steps.The challenge procedure starts with tiny doses of the medication that we gradually increase to the goal dose. Should the patient have any reaction, we will stop the medication and treat with supportive therapies.

What treatments are available for drug allergy?

Avoidance is the only way to prevent reactions.  It is important that you tell doctors and pharmacists about your drug allergies.   You should carry identifying information about serious drug allergies such as a card in your wallet or a bracelet.  Accidental exposures to the medication in question should be treated immediately with the appropriate medications.

Sometimes, a drug you are allergic to may be the best treatment for your condition.  Depending on your prior reaction, you may be able to undergo a drug desensitization procedure.

What is drug desensitization?

For certain types of drug allergies, a drug desensitization procedure can temporarily allow you to tolerate a medication you are allergic to, especially if you absolutely need this medication.  To be done safely, this procedure must be closely supervised by experienced allergists with the help of nurses and pharmacists.  It involves starting with tiny doses of the medication, and doubling the dose slowly until the full dose is taken.  The desensitization is temporarily stopped if there is any sign of allergy, and the reaction is treated.  When you recover from the reaction, the desensitization starts again.

It is not completely clear why this works, but it seems that this process makes allergy cells "nonreactive."  Desensitization is not a cure, but does allow temporary use of the medication as long as it is given at least once a day.  If you stop taking the medication for a day or longer, the process has to be repeated.  A typical procedure takes many hours to days to complete, and most reactions are mild.

How does drug desensitization work?

We offer drug desensitization in the inpatient and outpatient setting. Drug desensitization is generally performed only if medically acceptable alternatives do not exist and only when any other concurrent health issue is under optimal control.

This is a >4 hour procedure that allows a patient who is allergic to a medication to temporarily tolerate the medication when it is medically necessary. The desensitization procedure starts with tiny doses of the medication, and we gradually increase the medication to the goal dose, treating any signs and symptoms of an allergic reaction as it occurs with supportive therapies. At the end of the procedure, the temporary tolerance will remain as long as the patient continues to receive the medication regularly. If there is an interruption in use of the medication, an allergy evaluation is needed as the patient will need a repeat desensitization procedure.