Last Updated on December 18, 2025
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Think you have a drug allergy to penicillin? Or maybe it was another medication you took years ago? The truth is, many of us walk around with a drug allergy reaction noted in our medical records that may no longer be accurate… or were never true allergies to begin with.
Having a drug allergy reaction correctly documented on your chart can massively impact your care and what medications you have access to.
So if you no longer have a penicillin allergy, but it’s still on your chart… you might end up being given treatment options that aren’t ideal.
And on the flipside, you can develop a drug allergy later in life!
This shocking information about drug allergies will be surprising.
In today’s episode, I’m joined once again by Dr. Mariana Castells. We’re diving deep into how drug allergies are diagnosed, what actually counts as a drug allergy, and why some drug allergy reactions may disappear over time. Plus, we unpack how something called “drug delabeling” could open up better treatment options and protect you from more serious side effects caused by substitute medications.
Mariana Castells, M.D., Ph.D., is a physician and researcher at Brigham and Women's Hospital with over 30 years of experience in allergy and immunology. She is Director of the Mastocytosis Center, one of the few nationally and internationally recognized centers of excellence providing diagnosis, management, and treatment options for patients with mastocytosis and mast cell activation disorders.
Dr. Castells is also the Director of the Drug Hypersensitivity and Desensitization Center, which provides over 900 high-risk desensitizations per year for over 20 years to patients with cancer, severe infections, and inflammatory diseases who are allergic to their first-line therapy.
Let’s get into it!
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In This Episode:
- The difference between a side effect and a real drug allergy reaction
- Why you shouldn’t automatically blame meds if you get hives or rashes
- How to safely test for a drug allergy (like a penicillin allergy)
- Drug delabeling: What is it?
- Safer antihistamine options to choose OVER Benadryl
- Why adults develop allergies later in life
- The most common signs of anaphylaxis (and when to use an EpiPen)
- What Stevens-Johnson Syndrome is and why it’s so serious
- Is a drug allergy a genetic issue?
Quotes
“80% of the time when we have a manifestation in the skin after taking a medication, it’s more likely that the cause of us taking the medication induces the rash, not the medication itself.”
“Drug allergy is not forever in the majority of people.”
Links
Find Dr. Mariana Castells online
Healthy Skin Show ep. 327: Demystifying Food Allergy Signs, Symptoms + Skin Rash w/ Dr. Ruchi Gupta
Healthy Skin Show ep. 400: Is Tylenol Safe? The Acetaminophen Side Effects That Wreck Your Liver
407: When A Penicillin Drug Allergy (Or Allergic To Other Meds) Goes Away: How To Figure This Out w/ Dr. Mariana Castells {FULL TRANSCRIPT}
Jennifer Fugo (00:06.988)
Dr. Castells, I am so honored to have you back on the Healthy Skin Show. Thank you for joining us again today to discuss drug allergy.
Mariana Castells (00:13.53)
Thank you so much for inviting me again. I hope there is more hunger for allergies and some of the diseases that we encounter in the daily living, like either environmental allergies, food allergies, or drug allergies.
Jennifer Fugo (00:26.444)
Yeah, I mean, I will say that allergies fascinate me because they are more complicated than, a lot of times, what we think they are. So I have a drug allergy, at least I think I do. I think I'm gonna learn a lot from you today. As a teenager, I was exposed to erythromycin and I developed hives (drug allergy skin rash) everywhere from taking it, but I'm now 45 and I still tell people that I have this allergy, though I've never been exposed to it. And some of the things that you've shared with me before we started recording are making me wonder, maybe my assumption wasn't exactly correct, I have no idea. But it sounds like drug allergies, which can happen, it's not just like, you might have this for life, like there actually is maybe a pathway to becoming free from that drug allergy.
So with that being said, could you share with us what is a drug allergy, and what are the differences between some symptoms that are, like we might as the patient think, oh, I have an allergy, but aren't really signs of an allergy, versus what would be signs of an allergy?
Mariana Castells (01:40.518)
Yeah, that's a great question. For example, somebody taking an aspirin or ibuprofen, having abdominal pain, a little bit of regurgitation, that is a side effect of the medication. Somebody taking an antibiotic and having a headache, that is a side effect of the medication. That is not an allergy. An allergy is something that is unexpected, that occurs pretty quickly. Some of the more acute reactions, within hours of taking a medication, sometimes a little bit days after taking the medication, and that leads to, mainly, the more common presentation is like something in the skin. So either hives, or an itch, or a rash. And that actually is kind of the telltale sign that there is a reaction occurring, and most of the time within hours of taking an amoxicillin and ampicillin tablet, there is such a reaction.
Now I have to say that the majority of, for example, antibiotics that we take are for a good reason. So there is an underlying infection. So a child taking an amoxicillin tablet is because she has an infection, whether it's tonsillitis, whether it's a sinus infection, whether it's bronchitis. At the same time that we put that antibiotic, there is a virus or a bacterial infection that can also induce the rash. So again, 80% of the time when we have a manifestation in the skin after taking a medication, it’s more likely that the cause of us taking the medication induces the rash, not the medication itself.
Unfortunately, when somebody has a rash after taking a tablet of penicillin or amoxicillin or ampicillin, that is noted as an allergy, and about 20% of the general population in the United States claims to be allergic to penicillin. But when we evaluate that allergy at the time when the patient needs, when someone needs, again, an antibiotic, like at the time of a pneumonia or some other infection, at that time we realize that the allergy is lost or there was never an allergy in the first place. And the process is called delabeling.
Mariana Castells (04:08.134)
So it's critically important that when someone has somebody in the family presenting a reaction after taking a medication, that the causality be established so that there is a clear interaction between taking the medication and presenting the symptoms. And that can be done by an allergist. So after having a drug-induced reaction, whatever the kind of reaction, that being seen by a specialist is critically important.
Jennifer Fugo (04:33.952)
Yeah. With this, does it matter the exposure, so topical, say ointments, versus an oral, versus an IV med, does it differ? Is there a time delay between them that might be differing, or is it pretty much, like you said, within a few hours?
Mariana Castells (04:54.456)
Well, the timing is important, but also the presentation is important. For a topical, mostly it stays around the place where the drug has been exposed. So with a topical, it would be redness at the site, so we can identify that place. With the oral, the symptoms can be, like we were saying, like hives, and can be hives everywhere, but that can happen within one to six hours. With the intravenous medications, it's more immediate. It is within the time where the medication is being given, at the time of the infusion. So those are kind of the quickest ones, and potentially the more severe because that is introducing to the bloodstream and it can be what we call systemic reactions.
Jennifer Fugo (05:36.685)
Wow. Yeah. And is this a little different, like, so I know that with topical antibiotics, I had an allergist who talked about the problem with the, goodness, it's like the neomycin, bacitracin ointments, and polysporin, I forget, it's like the triple antibiotic cream that you can buy at the pharmacy. He's like, there's a lot of problems with that with an allergy because you can develop contact dermatitis. Is that a form of what you would consider a drug allergy skin rash, or is that a different type of reaction?
Mariana Castells (06:14.16)
No, that's a form of drug allergy, which is actually localized. And then normally when you reapply an ointment, then there's redness of the skin, there is itching of the skin, there may be hives, or maybe a rash. So that is due to a type of cells in the body that are called T cells that are in the skin, and then every time that this is applied, there is the initial sensitization, so the cells learn about it, and then they develop that rash. That rash may not be that severe, and that may not be to the rest of the body, so it can stay here. For example, poison ivy is similar to that. When people have poison ivy, they get the contact here, but sometimes the contact leads to a more systemic reaction, but we can identify the place where the contact occurs. So those are reactions that we say are limited, for example, to the skin.
But then there are the more severe reactions, for example, the penicillin reactions where penicillin is ingested or there is an injection, intramuscular or IV. And that can lead to what we call anaphylaxis, which is a reaction that can go with multiple organs, from the skin hives, to nausea and vomiting, to respiratory, like the lungs can be shut, the throat can be really tight. And then there can be some dizziness and some sense of impending doom, and sometimes there is, like patients pass out, and they need an epinephrine injection with that which is what would reverse the anaphylaxis.
Jennifer Fugo (07:47.139)
Right. Can I ask you really quickly too, because I've had, like I said, allergies and drug allergy reaction have been a topic that I'm fascinated by. Do you still feel that, especially with parents with kids at home, and this isn't just a conversation about kids, because obviously this can impact adults too. Do you still feel that Benadryl is like the thing to have in your house for allergies? I've had some dermatologists say, or actually allergists, like Dr. Ruchi Gupta who connected us, she really feels that maybe Zyrtec is a better option to have on hand if you feel like you're starting to present with these types of allergic symptoms that could possibly progress to anaphylaxis. What's your thoughts? And would that apply to drugs?
Mariana Castells (08:37.67)
Benadryl was the only antihistamine that we had about 30 years ago, and it's been phasing out because the onset of action of Benadryl is within a few minutes, but after an hour, then it decreases. So it can really not sustain a protection. Cetirizine, fexofenadine, Claritin, those are long-term antihistamines that have prolonged actions, and the one important thing is that they go in good to the brain, they don't cross the blood-brain barrier. So with Benadryl, people are extremely tired.
Jennifer Fugo (09:15.256)
Yeah.
Mariana Castells (09:31.14)
They are somnolent, they cannot drive, they cannot do heavy machinery, they cannot take a test, they cannot really do things that require the whole brain. With non-sedating antihistamines, we can actually do all those actions, and the action of those antihistamines is 12 to 24 hours. So we don't use any more Benadryl in our clinics, we use either cetirizine, fexofenadine, or Claritin. Those are the powerful antihistamines.
Now, having said that, when patients go to the hospital and they have had an allergic reaction, the only IV antihistamine available is still Benadryl. So they will still be injected with Benadryl. Cetirizine is available IV and it's coming to the clinics, so I think that we will be shortly having that also available. And again, the prolonged action and the lack of sedation are phenomenal. In children, there are studies that say that children that were treated with Benadryl had seizures.
Jennifer Fugo (10:21.484)
Wow.
Mariana Castells (10:28.966)
So seizures have been associated because Benadryl goes to the brain. In people who actually overdose on Benadryl or take it in a chronic way, it's associated with dementia also, so changes in the brain. So again, long and prolonged use or high doses of Benadryl are not recommended at all.
Jennifer Fugo (10:38.946)
Now, let's just say some of these other antihistamines that you're saying you now lean towards, if this, say, happened at night, or you woke up in the middle of the night and you've got hives, these medications aren't gonna keep you awake? Obviously some people are like, well, I wanna take Benadryl then because I wanna go back to sleep. But would these medications still allow you to sleep if you needed to?
Mariana Castells (11:03.312)
They will allow you to sleep, they won't keep you awake. They don't have, they're just not sedating. So the Benadryl will put you back to sleep, definitely. So again, taking a Benadryl here and there is not something that would harm people, but again, it will not lean onto protection. For example, if somebody says, I have hives in the middle of the night sometimes, if you take a cetirizine, you can sleep through the night, the hives will not happen. If you take a Benadryl before going to bed, the hives will happen at 2 a.m. because there is only two or three hours that Benadryl will protect. So prolonged protection is not afforded with Benadryl.
Jennifer Fugo (11:43.83)
I appreciate you for clarifying. I feel like every time I ask these questions, I get a little bit more information that is super helpful for everyone. I feel like if more people knew and understood some of, at least this basic stuff about allergies, like I kind of, maybe it's because my dad was a doctor, we always had stuff in our medicine cabinet and whatnot, but I feel like there's some basic things. Like if you think about having a kit at home, like a first aid kit or something, I do think that it's a good idea for everybody to have something like this just in their house. You may never need it, but if you do, it's there. Similarly to Tylenol or Band-Aids or something like that, just in the event, because we shouldn't assume, and this is something else I've learned, we shouldn't assume that it's just children that can develop allergies, because we can develop allergies as adults.
Mariana Castells (12:40.29)
Absolutely. Food allergies, drug allergies are things that we can develop as adults, at any age. We had an 80-year-old who developed a food allergy very recently to crustaceans, but the first 80 years of their life, nothing has happened. So again, allergies are on the rise. As a developed society, more clean society, less outdoor interactions, our immune system has a tendency to develop allergies to foods, and medications, and environmental things, and so that's going to be on the rise. So I absolutely agree with you that having cetirizine at home potentially. If somebody has ever had an anaphylactic reaction, they need to have their doctors write a prescription for epinephrine, and epinephrine has come in two options. There was only a needle that was available before, and people sometimes don't really like needles, and particularly for kids, there's like a nasal spray that can be used and was just approved.
Jennifer Fugo (13:40.174)
I know, that's new. That's new. I think that just got approved this year, in 2025, in the US.
Mariana Castells (13:45.696)
Exactly. And that is a fantastic medication that you can use without a needle, and it will have the exact same effect as the epinephrine injectable.
Jennifer Fugo (13:54.732)
Yeah. So let's talk a little bit more about drug reactions and what happens. So number one, can you take a drug for many, it sounds like this is possible, you could take, let's just say penicillin. You could take penicillin for many years, right, whenever you needed it. I'm not saying every year, hopefully not, but let's just say you take it 10 times throughout your 70-year-old life. And for some reason, this one time something happens that never happened before, and all of a sudden it sounds like you would develop some sort of rash, hives, maybe some swelling in the mouth, I have no idea, but that is possible, yes?
Mariana Castells (14:34.138)
That is totally possible. And the reason being that the infection that you're trying to use the penicillin for is a different type of infection. We had COVID-19, we never knew the new COVID. COVID other numbers, yes, coxsackieviruses were there, but never the number 19. So it can be depending on the kind of bacteria, virus, whatever the infection, it can be also depending on hormonal changes, for example, in women. During menopause is very different, and then there's a lot of things that change in menopause that may make the immune system more aware of medication.
People who also are treated for, say, cancer, or some other inflammatory diseases, change their immune system. There is a lot of things that can change your immune system. Taking antibiotics for a long time for, say, a Lyme disease, or some other, can also change what we call the microbiome. So again, there is a lot of internal and external things that may make your immune system different, and may look at medications in a different way. So anyone can become allergic anytime in their lives.
Jennifer Fugo (15:44.27)
Okay, and the most severe, what would you, obviously we have anaphylaxis, that's pretty severe. I think most people are familiar with anaphylaxis because we know your throat can close, you can stop breathing, you can potentially die, like you said, if you don't get that injection of epinephrine. But there's also something called Stevens-Johnson syndrome, which most people probably haven't heard of. I, fortunately, came across an article about this like 20 years ago and asked my dad who was a surgeon about it, so I'm familiar with it, but I don't think most people are. So do you wanna talk a little bit about that?
Mariana Castells (16:20.71)
So like you were saying, anaphylaxis is a broad-spectrum thing. Anaphylaxis can start with somebody having just an itch and hives, and then that can actually progress to the throat itching, and then throat closing, and then they're having an elephant in their chest, and then ended up throwing up, and then the blood pressure goes down. And that, it can happen like that in one single time, or it can be that at times we only have two.
And essentially the anaphylaxis happens when two organ systems are affected. So if there is the skin and the respiratory, or the skin and the gastrointestinal, or the skin and the blood pressure, like feeling this tunnel vision, and feeling passing out or impending doom, those things are not well known because a lot of people say, oh, I didn't know that if my throat was feeling tight and I was feeling dizzy, I needed to use my EpiPen. Well, the answer is yes, because two organs means that the reaction is systemic. But again, in acute reactions, we can have just hives, hives and itching and flushing, and that would be kind of a mild reaction. A moderate reaction will be if there is more, and then the severe reaction has the anaphylaxis. And again, the use of the epinephrine is mandatory, so people would need to use, immediately, the epinephrine. It saves lives, and it prevents the reaction from progressing.
Now those reactions are typically acute reactions. They occur when we take medication either orally, or intravenously, or intramuscularly, and within one to six hours there is something happening, we start to scratch, to itch, you have throat tightening. The other reactions, that are called delayed reactions, are reactions that are not mediated by the same cells of the acute reactions, which are called mast cells, but by T cells. And those T cells take some time to react, it may take days. So the patient takes, for example, a Bactrim, a sulfonamide medication, and within 10 days or seven days, then they start to have a rash, and it's not very itchy, it's more burning. And then suddenly there is blisters in that rash. And then there is, like the mouth has sores, vaginal lining can have sores too. The patient feels really bad, there might be a fever.
And that can lead to what we call Stevens-Johnson, which is a very dreadful type of presentation. The skin can blister, patients will need to be admitted to the hospital, and eventually going to the intensive care unit. There is treatments for this, but the important message is that they have to identify what medication they used that induced that, and then avoid, always, that medication because those reactions are for life.
Jennifer Fugo (19:13.134)
And so, you're saying that if you had one, we'll say episode of Stevens-Johnson syndrome, if you were exposed a second time or a third time, you again will have an episode like that.
Mariana Castells (19:27.702)
Yes, and those episodes can be more severe on second or third re-exposure.
Jennifer Fugo (19:30.871)
Oh, wow. Okay.
Mariana Castells (19:54.406)
We are learning that a lot of those reactions are mediated by a certain barcode in our genes that's called HLA. So the HLA is like a barcode that we inherited from father and mother, and also from grandfathers and the genetic family tree. And we are learning that some patients have this HLA, specific HLA, they are more prone to develop reactions either to sulfonamides, also to anticonvulsant medications, and other medications. So there is nowadays a lot of research trying to understand why people would develop that, and sometimes why two people in the same family will develop that, because that HLA is transmitted genetically from the grandparents to the children. So that is something really important, the genetic makeup for those reactions.
Jennifer Fugo (20:29.002)
So in terms of testing for drug allergy, is there testing or is it just like, oh no, we had this reaction to this or we suspect, like how do you know for sure that you have a confirmed drug allergy? I mean, I had hives, so I'm assuming that my erythromycin incident was confirmation of an allergy, but you know better.
Mariana Castells (20:52.378)
Well, there are three interesting facts here. One is that allergies, after a few years, have a tendency to disappear, they don't stay for life. So we say that penicillin, after 10 years, if there were 100 people allergic to penicillin, 10 years later, there is 10 people.
Jennifer Fugo (20:54.217)
Oh my gosh!
Mariana Castells (20:55.927)
And then 20 years later, there is one [person]. So the immune system has a tendency to actually forget about those, and it doesn't really register it again. The second thing is that the hives can come from the infection, as we were saying, and it was never the drug. So again, that is kind of a mislabel that we have. So delabeling can be done, absolutely.
We can actually do testing for most drugs. We put a little drop on the arm and we then see if there is a little bit of an itch, like a mosquito bite type thing, and if that itch, means yes, you're still allergic, we compare that to a positive control, that's called histamine. But if there is no such thing, then we say, well, what about taking it here in front of me, and you're sitting in a chair, and then I will monitor what happens. And then nothing happens, and you go home, and nothing happens. And you are, quote unquote, de-labeled, you can take, again, that medication. So the majority of the population, and 20% of the American population is thought to be penicillin allergic. When we examine them, when we do the evaluation, when we de-label those people, less than 1% will be allergic.
Jennifer Fugo (22:23.15)
So when I read your, you had given me some great guidelines just to ask you questions, because obviously I'm not an expert in this area. This is very new, so I'm coming at this from a patient's perspective. And I was like, delabeling? You mean you take the label off the container? And I looked it up and I'm like, oh, it's removing it from basically your medical record, and saying you're no longer allergic to this.
Mariana Castells (22:44.742)
That's right.
Jennifer Fugo (22:51.788)
So I got to learn in real time. And what I found fascinating, and I'll put this, this report is from 2020, it was printed in a journal where basically they discovered that so many people had said that they had, as you said, penicillin allergy or penicillin allergy reaction. And with the advent or shift to electronic medical records, it was actually discovered that something like only 5% of those people actually had that allergy, and so we wanted to remove it. And like you said, it's actually a good thing, right? We wanna get those labels off of an allergy if you don't have it anymore. Could you give a few, maybe like a reason or two why, or examples as to why it would be good if you did remove an allergy that you're actually no longer allergic to?
Mariana Castells (23:33.894)
So I had this woman, a patient of mine who came to the clinic after she had had a pretty bad pneumonia and she was admitted to the hospital. She told her doctors that she was allergic to penicillin. They gave her a couple of substitutes, one of them being vancomycin. She developed one of the most common severe side effects or complications, which is severe diarrhea. She was infected with another bacteria, which is called C. diff, and she had to spend 10 days in the hospital. She said to me it was the most horrendous experience I've ever had, not because of the doctors.
Jennifer Fugo (24:09.987)
Right.
Mariana Castells (24:33.768)
But because I saw myself sinking. And she had pneumonia, she was treated with antibiotics that were not penicillin, and she almost died. So she came to me and she said, I heard, Dr. Castells, that maybe I'm not allergic to penicillin. And then we started to do the delabeling process. How long ago? Oh, my mother told me. Did she tell you you went to the hospital? No. Did you remember anything about that? I don't. And I said okay, that looks like a low risk. We did penicillin skin testing, it was negative, it took about 15 minutes.
And then the big time came, can I put a penicillin tablet in your mouth, would you allow me to do that and then monitor you for the next hour, and then decide that you either never had a penicillin allergy, or you lost your penicillin allergy. She was really, really, really, shaky at that time. She didn't know how it would do. Then she did it, and within an hour there was nothing happening.
Jennifer Fugo (25:09.72)
Wow.
Mariana Castells (25:32.806)
And then I said you're delabeled. She was very happy. She then had another episode where she needed an antibiotic, she was able to take amoxicillin, ampicillin, penicillin. And then she sent me a note and it said, Dr. Castells, why didn't you tell me this before? Why people do not know that before? And I said, that's exactly right. This is the need, the unmet need, because at the time of the infection your doctors have their hands tied, they cannot delabel you at that very minute. They can just listen to you, I had this reaction, I don't know what it was, it could be severe, I have no idea. They cannot do skin testing at the time of a severe infection. So delabeling has to be happening before the time where the antibiotic is needed.
Jennifer Fugo (25:54.668)
So what I'm hearing you say is that for anybody listening to this who has been told, or in the past, maybe as a child and now they're an adult, has a penicillin allergy or penicillin allergy reaction, it actually is a good idea, in the event that you do need it in the future, and none of us have a crystal ball, so we don't know what's coming down the pipeline for us, that if you can get that delabeled, if you truly don't have that allergy, that could potentially mean you have a lot more treatment options than what you would if you went to the hospital in, like you said, pneumonia or something like that where you actually need to take those medications.
Mariana Castells (26:37.462)
Absolutely. And I would say, I would even be kind of stronger than that, I would say always question any drug allergy that you have been told you have. Even if at the time where they give you a medication, even Bactrim, they give you this medication, or erythromycin, or a penicillin, and then you had some hives or a rash, question that. See a specialist that can truly, truly see the correlation between the medication and your symptoms.
So again, I would question any of the drug allergy labels that people have and see a specialist to say, it true that I have a penicillin allergy, or is it not true? Because, and the reason is, like you said, you are going to be offered the best medication for your treatment. And that would be what we call the first line. You can get penicillin. There will be less time of staying in the hospital because you're treated with the best medication. There would be no complications with other medications that are not your first line. And so it's been shown that we shorten the time where the patient needs the antibiotic, we shorten complications, we shorten hospital stay. So it's really dramatic. And in the worst case scenarios, if you are not able to be getting that particular medication, things can go very south.
Jennifer Fugo (27:59.256)
Sure.
Mariana Castells (27:59.258)
Very south. On the other hand, if there is this potential that the label remains true, and the 1% of the people who are truly allergic to penicillin, we have actually developed a new modality to treatment, which is called desensitization. And desensitization is not removing the label, it's not making you less allergic, it's like tricking the immune system so that you can receive the medication.
So we have, for example, for people who have cancer, and a woman with ovarian cancer, the cancer comes back, she has been treated with really good medications, ane of them is called carboplatin. And 27% of the women who have ovarian cancer and who are treated with six treatments with carboplatin, 27% will become allergic. It's a lot.
Jennifer Fugo (28:53.133)
Yeah.
Mariana Castells (28:57.466)
A lot of them. And they will continue to respond to that carboplatin, but a lot of them are switched or were switched to another second line medication because they were truly allergic and had anaphylaxis. So in my laboratory, we have investigated what we call inhibitory mechanisms of mast cells, and we are able to come up with a formula, that actually dividing the dose in small steps, like what we call baby steps, we're able to put back that carboplatin, that penicillin, that medication, back to the patient when they need it and be able to tolerate that medication.
Jennifer Fugo (29:29.432)
Wow, that is amazing!
Mariana Castells (29:30.968)
It's great, it's absolutely great. We are now, we have a center for desensitization here, which is probably the biggest in the country and the world, where we do about a thousand desensitizations per year. So we are able to desensitize to antibiotics, to chemotherapy, to monoclonal antibodies, to anything that a patient is actually in need for first line therapy. We don't desensitize if the patient has an alternative medication or can be treated differently, but for first line. And for cancer, there is not many first lines, let's put it that way. There's one drug that really addresses the cancer, and the rest would be second line. So we are honing on that.
And then for patients, for example, with a disease that's called cystic fibrosis, where patients have lots of infections, there's one good antibiotic to treat, and we can desensitize to that antibiotic. Or for patients with inflammatory bowel disease, or any rheumatoid arthritis, they have a monoclonal antibody that is the best for them. And then they become allergic. We can put that back.
Jennifer Fugo (30:36.878)
That is amazing. I love learning, this is why I do this. I absolutely love this. And I think, so I just want listeners to know number one, the whole point of this conversation is not to be like, oh, yay, we should, we want to take antibiotics. But the reality is when you need them, and it's usually inconvenient, and you don't expect it, nobody plans to get sick. But there's a time and a place. Like, I don't want to take antibiotics if I don't need them, so I don't blame anyone for being gun shy or nervous. This isn't about saying like, we should just take them all the time. Because obviously, there are concerns with actually overusing and overtaking antibiotics for the gut microbiome, as you said.
Mariana Castells (31:21.22)
Absolutely.
Jennifer Fugo (31:29.326)
But this is about having more options. As you pointed out, to develop a C. diff, which is a very serious infection and has tons of long lasting issues associated with it, because you just couldn't take penicillin, it's not good for your health longterm.
Mariana Castells (31:40.795)
Right. And the delabeling process, again, is just knowing it and then choosing a specialist and allergist, and it takes, usually a delabeling process may take an hour.
Jennifer Fugo (31:52.887)
Okay.
Mariana Castells (32:07.782)
So it is really an easy process, but mentally we have to be prepared and we have to question the notion that drug allergy is not forever in the majority of people. Yes, there is a population that will remain allergic to penicillin for their lives, likely because of their genetic makeup, but the majority of the population loses their penicillin allergy and never come back to be allergic. So 90%, of the time or 95% of the time, we can delabel most people.
Jennifer Fugo (32:27.886)
And I think this might be a really great final question, because I just want to hammer this home. If you took antibiotics and you got GI issues like diarrhea, which is, I believe, a fairly common side effect.
Mariana Castells (32:43.62)
Correct.
Jennifer Fugo (32:45.301)
Would that be considered a possible allergy? Or would you say, no, that's a side effect of the medication?
Mariana Castells (32:52.262)
Correct, it's a side effect. So for an allergy, you need, really, to have either a drug allergy skin rash or two organ systems that are involved.
Jennifer Fugo (33:01.794)
I think that's helpful for people to know because I, in the past, have been like, I was three days into amoxicillin and I ended up with horrible diarrhea, I must be allergic to it. And I think having these boundary lines to help educate us to understand what's happening better, because I understand doctors don't always have the time to go into all of this. So this is a really great opportunity for everybody out there to understand this better, and to know, number one, your center exists. Number two, they can also work with a local allergist on this delabeling process. And if they need more help with the desensitization and whatnot, your clinic is available to them.
Mariana Castells (33:39.044)
If they can use desensitization, the word, they can google that or GTP and then put my last name, they'll have a ton of information, definitely. And many centers now do those desensitizations. I have to also tell you that the same principles for desensitization are used for oral immunotherapy for foods. So people allergic to peanuts use our protocols to do that peanut oral immunotherapy, the same thing.
Jennifer Fugo (34:08.514)
Wow! That is amazing. I'll tell you, science is just so fascinating. There's so much we don't know, and when you learn things, it's like, wow, this is so cool. Well, I will definitely, so number one, I'm going to link up to our previous episode, because I think for people who want to understand histamine and mast cells and such, it was such an informative episode. And then I'm also going to make sure to link to you, in the event that someone does want to come see you and work with you directly.
Mariana Castells (34:33.304)
Of course, of course.
Jennifer Fugo (34:38.08)
But I am so appreciative that you've given so much time to sharing your knowledge, your vast knowledge, and also making it digestible for people who don't understand any of this because it can be very overwhelming. So thank you so much for just your willingness and your, gosh, you're just so, gosh, the word is eluding me, of course, but you are so gracious with your time and giving with your time and it really means a lot, so thank you.
Mariana Castells (35:08.166)
Thank you so much. Yeah, I really appreciate you having me because I think, you know, as humans, we are going to have more and more wonderful and targeted medications, but we'll have to pay a price. And I think that everybody should know that adverse events with medications are coming our way, but there is ways to address that. Thank you so much. Thank you.
Jennifer Fugo (35:26.766)
Yeah, thank you.
Mariana Castells (35:27.943)
Have a great day. Yes. Bye bye.
