What allergies do you have to medications?

You are probably recalling years ago, perhaps even decades ago, of that time your parents told you had a rash to an unnamed medication ending in “-cillin” when you were a child, or that one time you developed a rash after taking something for infection. Was it really a true penicillin allergy? And why is this question so important

First, what are penicillins?

Penicillins are a group of beta-lactam antibiotics that kill bacteria by breaking down their cell walls. Penicillin antibiotics are used to treat ear infection, throat infection, sinus infection, dental infection, surgical infection, and many others.

Penicillin drugs, some of which you may be familiar with, include but are not limited to penicillin, amoxicillin, amoxicillin-clavulanic acid, ampicillin, piperacillin.

How does penicillin allergy occur and how common is it?

Penicillin allergy occurs when your body recognize it as a foreign threat, and consequently triggers an immune response against it. Immune responses could range from a skin reaction that goes away on its own to a full-body allergic reaction. CDC approximates that 10% of patients in the U.S. have reported as having an allergic reaction to a penicillin-class antibiotic in the past – but upon testing, less than 1% of these patients have a true allergy to penicillin. This means that out of 100 people that have reported penicillin allergy, the chance that even 1 person truly having a penicillin allergy is very unlikely. The rate is astoundingly low! Furthermore, studies have shown that most patients become tolerant to penicillin allergy over time, even those with severe allergic reactions to them.


Special note! Penicillin allergy is not inherited. Your immediate family’s allergy to penicillin does not have any implications on your own allergy/ability to take penicillin.


So why are allergies to penicillin so frequently reported?

Penicillins are very effective antibiotics, making them some of the most commonly prescribed antibiotics to treat a wide variety of infections – hence responses to penicillins are frequently reported.

Why is it important for us to identify if you truly have an allergy to penicillins?  What’s the big deal?

When you have penicillin allergy reported in your health profile, your health care team will likely avoid penicillin, even if they are the most effective antibiotics for your infection. Providers would instead choose alternatives or broad-spectrum antibiotics to avoid any potential harm. This practice is not ideal as broad-spectrum antibiotics increase toxicity, and overuse can lead to an increase in bacterial resistance, as well as other infections such MRSA (methicillin-resistant staph aureus), and Clostridium dificile. By accurately identifying your penicillin allergy, we can reduce these unnecessary harms and provide the safest, most effective therapy.

What are the types of reactions to penicillins? Which reactions indicate true penicillin allergy

 Side effects include: 

  • Diarrhea, nausea, upset stomach, headache, fatigue

Allergies include: 

  • Immediate life-threatening allergic reaction: within hours
    • rash, hives, swelling
    • shortness of breath/tightening of airway
    • drop in blood pressure
    • seizures, loss of consciousness
  • Delayed allergic reaction: days to weeks
    • serum sickness, drug-induced anemia
    • severe skin reactions:
So does my rash mean I’m allergic to penicillin or not?

Developing a rash to penicillin antibiotics does not necessarily mean you have a true allergy to penicillin.

Penicillin rash accompanied by shortness of breath, hives, swelling, drop in blood pressure, increased heart rate, and/or loss of consciousness indicate true penicillin allergy and should be avoided.

Penicillin rash that is not accompanied by these symptoms and is flat, blotchy, spreads over days (does not change by the hour) and typically starts days into therapy typically indicates non-allergic penicillin rash and should be tested to rule out allergy. It is important to discuss the timeline, presentations, and resolution of your allergies with your care team.

What are test methods to identify if you have a penicillin allergy?
  1. Direct oral penicillin/amoxicillin drug challenge:
    • Takes place in outpatient/hospital/clinic setting.
    • Receive 1 dose of penicillin in office and observe for 1 – 2 hours.
    • Safe and effective method for patients in which penicillin allergy suspicion is low.
  1. Skin test:
    • Takes place in outpatient/hospital/clinic setting, typically immunology clinic.
    • Non-invasive, not painful.
    • Results available in 45 minutes.
    • Safe and highly effective method for patients in which penicillin allergy suspicion is high.
    • More accurate than oral challenge test.
What can you do?
  • Take a picture of any rash that forms.
  • Talk to your primary care provider about your penicillin allergy.
    • What medications were you on at the time?
    • What were you being treated for?
    • What symptoms did you encountered?
    • When did it happen?
    • How long did the symptoms occur?
    • Did you have to go to the ED/hospital for it?
    • How did it resolve?
  • Discuss with provider about getting an allergy test to confirm.
  • Share with your pharmacists any reactions during your allergy incidence so we can document them clearly.
What do your pharmacists do? 

Your pharmacists routinely review your medications and check to make sure they are safe and compatible for you according to your age, medical condition, and known allergies. Studies found that pharmacists, who are experts on medications and disease managements, are some of the most knowledgeable health providers in penicillin allergy. They communicate with your doctors about any concerns relating to your health or medications, and advocate for your needs. Hence discuss your allergies with your local pharmacists to help them ensure that your care is safe and effective.


Prepared by:  Tiffany Dang, UWSOP PharmD Candidate 2022


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