Elena Resnick
Appearances
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
Huh. This patient told me they were allergic to penicillin. Oh, it's that your mom told you when you were a kid. Well, what happened? Oh, you don't even know what happened?
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
Atenosylins are an amazing drug also because we know them to be safe and effective in pregnancy. When a pregnant woman goes in to deliver, if she is colonized with group B strep, which is a very common vaginal infection, she must be given antibiotics before delivery to ensure that the baby is not exposed to the group B strep.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
So the antibiotic of choice for group B strep is in the penicillin family. Mom comes in. She's ready to deliver. She gets a dose of penicillin. She gets her second dose four hours later. She delivers the baby. Everything is fine. If she is thought to be penicillin allergic, instead she's given vancomycin. Vancomycin dosing interval is every 12 hours.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
So if she's not dosed appropriately, the baby can be considered inadequately treated, and that leads to all sorts of other complications. Potential decisions, maybe getting put on antibiotics, maybe going to the NICU. Again, the complications just from this penicillin label are intense. So in this particular scenario, this mom went in to deliver. She was thought to be penicillin allergic.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
They gave her vancomycin. She developed Redman syndrome from the vancomycin, which is just what it sounds like, where the body is. becomes completely red and flushed and other medications have to be given. And then she had a wound infection from her C-section because she was still thought to be penicillin allergic.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
They gave her clindamycin to treat the wound infection, and she developed C. diff from the clindamycin. And how did that play out? So when you develop C. diff, then you have to be put on oral vancomycin and then treated usually for two weeks. It's just a nightmare. It's one thing after another. And then she came to see me and we were able to clear her of that penicillin allergy.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
So her OBGYN, we also rely on the OBGYNs to find people who in their charts have this penicillin allergy. The problem with that is we're not going to test a pregnant woman just on the off chance that she does end up being one of these rare people who's truly allergic. Obviously, we don't want to put a pregnant woman into anaphylaxis.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
So we're sort of stuck with that label, which is hard for the OB because then their patient gets a simple infection. They can't use a penicillin. So a lot of the OBs will say to their patients, before you get pregnant again, better go get cleared of your penicillin allergy.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
Elena Resnick. I'm an allergist and immunologist.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
I always knew I wanted to be a doctor. My dad's a doctor, and there was never any doubt about that. I was lucky to have a lot of great mentors along the way. My mentor in college, Jerry Groupman, who's up at Harvard, was very instrumental in my choices. I worked in his lab for four years. applied to medical school, thought I wanted to be a hematologist oncologist like him, explored that field.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
And later into my residency, I explored allergy immunology, which has fascinating medicine and amazing potential to make people feel better.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
The immune system in particular is fascinating because we know so little about it. It's so important, right? We need our immune system to protect us from disease and to fight things off. When it goes haywire, we can end up with autoimmune disease, which is where our own antibodies attack us.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
Or we can end up with allergic disease, which is when different types of antibodies, IgE antibodies, react against substances that are harmless. But if we make antibodies against them, we can run into big trouble. Define IgE for me. IgE is immunoglobulin E. It's an immunoglobulin that's made by B cells.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
It probably had more of a function evolutionarily in terms of fighting off parasitic disease, etc., It certainly was not evolutionarily made to react to peanuts and pollens, but we don't know why in some people those types of antibodies are made that are specific against harmless substances.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
It's the most serious type of IgE-mediated allergic reaction where the allergy cells explode, they release all sorts of mediators, histamines, tryptase, etc., and that causes your vessels to vasodilate. Fluid runs in, people get hives, people get swelling, people's throat closes up, or you have difficulty breathing.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
Your airways constrict. And because the vessels all over the body are dilating, your blood pressure drops. You can't get blood back up to your heart and you have a cardiac arrest.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
The studies show that 90 percent of people who believe that they are allergic to penicillin actually can tolerate it.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
Oh, my gosh. I don't know that I can think of any. I think that the vast majority of people either have or were told that they had some sort of reaction in childhood. So that is the most common history.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
I think you are 100% wrong, I'm sorry to say. The other drugs, we're so lucky to have them, but many of them have much more severe side effect profiles than penicillin does. They can have more serious complications. They're much more expensive. And in certain cases, for example, vancomycin, they can actually increase the risk of drug-resistant bacteria.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
How do we do that? So every good experiment has a control. And the controls that we use are saline, which is salt water. Nobody is allergic to that. And histamine, which is the body's allergic chemical. So we prick you. And when I say prick, I mean we clean off the forearm. And then we use tiny needles to introduce just under the surface of the skin saline, histamine, and our penicillin reagents.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
So it's four small pricks under the surface of the skin.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
If you are allergic, we would expect that where we pricked you with the saline, nothing would happen. Where we pricked you with the histamine, you'll get a red itchy bump. And where we prick you with the penicillin, you will also get a red itchy bump. That's considered a positive test. We say you've tested positive for penicillin allergy. That's it. Go home. Continue to avoid penicillins.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
If it's negative, we go on and do the intradermal test, which hurts a little bit more. We're using the same reagents, and we're putting them just under the surface of the skin. And again, we look to see, do those bumps get any bigger during the waiting period? And we're comparing them again against saline. If that test is positive, again, you go home. That's it. You're allergic.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
But if that test is negative, we now have a skin prick and intradermal tests that are both negative. And the studies show that in those cases, it's 95% likely that you'll then pass a penicillin challenge. I think in real life, it's probably much, much higher than that. But we go ahead and we do an oral challenge, which is just what it sounds. We give you a dose of a penicillin.
Freakonomics Radio
617. Are You Really Allergic to Penicillin?
We use amoxicillin, which is a common oral penicillin. We give you that dose. We have you wait in the office for about two hours just to make sure that you're fine. And that's the gold standard, right? Tests are tests. But if you take the medication and you're fine, then we know you're not allergic.