Do You Have True Penicillin Allergy?

Dr. Cosby Stone, a ​​Research Fellow in the Allergy Immunology Fellowship at VUMC, discusses prevelance of penicillin allergies, testing for true pencillin allergies, and how an incorrect drug allergy diagnosis may be harmful to an individual and society at large.

Begin Transcript

Welcome to this edition of the Vanderbilt Health and Wellness Wellcast.  I'm Shaina Farfel with Occupational Health.  Today, I'm speaking with Dr. Cosby Stone, a Research Fellow at Vanderbilt University Medical Center's Allergy and Immunology Fellowship Program.  Dr. Stone, thanks so much for being with us today.

Dr. Cosby Stone:  Oh, yeah.  Thank you for having me.  It's my pleasure.

Shaina Farfel:  Thanks.  So, today, we are going to discuss drug allergies, specifically to penicillin.  Dreaded by patients and providers alike, penicillin allergies can significantly impact a patient's treatment and plan of care but may not have to.  So, that's what we are going to discuss today.

Dr. Cosby Stone:  You bet.

Shaina Farfel:  First off, can you tell us the symptoms of a penicillin allergy?

Dr. Cosby Stone:  There's really two kinds of things that we worry about as being penicillin allergy.  One is the immediate symptoms that start with something like hives and then lead to nausea, vomiting, diarrhea, shortness of breath, and then swelling, and then loss of consciousness, low blood pressure, and shock.  That's called anaphylaxis.  So, that's a severe, immediate penicillin allergy.  Then, there is a category of severe delayed reactions where you have really bad skin rashes that can lead to blistering or fevers or organ injuries.  So, between those two, those are what we call penicillin allergy.  Then, in addition to that, there's a lot of things that happen to people while they are on penicillin that aren't allergy, and the vast majority of things that people think of as being penicillin allergy actually fall into that category where it's a mimic of allergy that isn't really something that you necessarily have to avoid the drug in the future.

Shaina Farfel:  What's the estimated number of people who have a documented penicillin allergy in their medical record versus the number of people who have a true penicillin allergy?

Dr. Cosby Stone:  At Vanderbilt, we looked at this recently and it is something on the order of 270,000 people who have contact with the Vanderbilt Medical system have a penicillin allergy listed in their chart, which is the something on the order of about 8% of our total Vanderbilt patient population.  Of those, in series of testing that we've done here in our clinic, when we test the patients who come to us from all walks of life, only about 1-4% of those patients actually will test positive to a penicillin.

Shaina Farfel:  That's a big difference there.

Dr. Cosby Stone:  It's a big difference.  So, there's tons of people who think that they are allergic to penicillin because of some event that happened to them at some point, usually in childhood, but the vast majority of those folks are not allergic to penicillin.  There's a couple of reasons for that.  One is that the initial events that people often call a penicillin allergy are actually not allergy.  So, amongst those things include, "I took it when I was a child and I had a viral infection at the same time," and viruses and drugs can interact with one another to cause rashes.  That's the most common reason for why you would end up with a penicillin allergy listed in your chart, actually.  Seventy-five percent of penicillin allergy labels are put onto a child's chart by the time they are three years old.  So, it’s usually these childhood virus-drug interactions that are causing people to get it put in their chart.  Another reason why people often have a label in their chart is because they have indigestion with a penicillin and antibiotics.  Antibiotics cause lots of indigestion and penicillin is no exception.  Amoxicillin is no exception.  So, nausea, vomiting, and diarrhea - people say, "Oh, I am allergic to that."  It wasn't really an allergy.  You shouldn't avoid the drug if you need it in the future, but it was something that made you say, "Oh, I think I'm allergic."  Why is a misdiagnosis of a penicillin allergy potentially harmful to an individual and then maybe to society at large?

Dr. Cosby Stone:  So, the complications that come from having a penicillin allergy in your chart when you have an infection are that you get a second or a third-line antibiotic.  Those second and third-line antibiotics can have side effects of their own and sometimes they are actually less effective.  By giving the wrong antibiotic in place of the penicillin that you think you have to avoid, you end up having longer hospital stays, treatment failures, and more likely to get surgical site infections.  So, we know all these things to be true based on research that others have done and some research that we've done here, and these are things that should be avoidable just by getting rid of the penicillin allergy that is no longer true, if it ever was true to begin with.

Shaina Farfel:  How do you test for a true penicillin allergy, and again, we touched on this a bit, but who are good candidates for testing?

Dr. Cosby Stone:  So, the people who are the best candidates for testing are the people who have had a recent reaction, if we are talking about immediate reactions.  So, if you had one of those immediate reactions, and you really want to know whether it was the penicillin that did it, coming in early and finding out as soon after the reaction as possible is going to give us the best chance of telling you the right answer.  And then if you have a severe skin allergy where, you know, you have that blistering skin rash or that severe skin rash along with organ injuries, something called Stevens-Johnson syndrome or DRESS, something like that, we can still do appropriate testing or give you advice on what you can take and can't take.  Now, all the doctors at VASAP and the nurse practitioners at VASAP, our allergy clinics here at Vanderbilt, can now provide penicillin allergy testing to low-risk patients who they have that history and they are still just not quite sure that they want to take a dose without having had a skin test beforehand, and we also have nurse practitioners who can do testing for people who have had those immediate, more concerning reactions, and then in our drug allergy clinics with Dr. Phillips and myself, we are going to be handling the medium and the higher-risk patients.

So, in our drug allergy clinic, whatever the patient needs, we are going to try to figure out how to do it, especially if you have a need for that drug and you think you might be allergic to it.  That's where we really will go to bat for you.

Shaina Farfel:  So, these sound like great services that you guys provide.  How do patients access them?  Is this something that is covered by insurance generally?

Dr. Cosby Stone:  It is, yes, and especially since I know that the majority of the listeners are going to be Vanderbilt employees, we take ... you know, the Vanderbilt insurances cover what we do, no problem.  Sometimes we have to go to bat for some patients who have different insurance plans, but we will do that as well.  Our services are covered and patients can access them.

Shaina Farfel:  Wonderful.  Wonderful.  Well, this has been very interesting, super informative.  I'm sure a lot of our listeners can relate to this issue, and now, knowing a bit more, will be able to access services, and so, thank you so much for your time today.  We really appreciate it.

Dr. Cosby Stone:  Absolutely, yeah, and if somebody wants to come see us, the main thing is just have your doctor put in a referral and try to be as detailed as possible about what happened to you and which drugs are the most important ones for you.

Shaina Farfel:  Wonderful.  Thank you so much.

Dr. Cosby Stone:  Thank you.  

Shaina Farfel:  Thanks for listening.  If you have a story suggestion, please email it to us at or you can use the "Contact Us" page on our website at