Why some drug allergies fade when our immune systems age

Published on Sunday, November 1, 2020

By: Gary Pettus, gpettus@umc.edu

Among the things we often lose as we age – hair, height, innocence, friends – there’s at least one departure we can get on board with: the loss of an allergy.

For instance, penicillin, an antibiotic you may want in your corner, is one of the most frequently accused drug allergens — but one that may be disarmed over time.

“Up to 95 percent of people who think they are allergic to penicillin are not, statistics say,” said Dr. Gailen Marshall, R. Faser Triplett Sr. M.D. Chair of Allergy and Immunology and professor of medicine, pediatrics, pathology and population health sciences at the University of Mississippi Medical Center. “So, many people are potentially avoiding a group of therapies that could really benefit them.

“When I was a kid, I took penicillin and got a rash. There’s a difference between getting a rash and having an allergy, but the doctor told my mother I was allergic, so I didn’t take it for 50 years. But as we get older, we can begin to lose that allergy, especially by age 65 to 70.

“Some people will lose it younger than that.”

There may be much to gain by that loss.

“If a penicillin allergy can be removed from certain patients’ medical records, it can make a tremendous difference for them,” Marshall said.

When penicillin was discovered by accident in 1928, it was considered a wonder drug, a treatment for blood poisoning, strep throat, scarlet fever, syphilis, tonsillitis, sinus infections and much more.

“Penicillin is in a class of drugs with many derivatives, and they’re still effective in treating multiple diseases,” said Dr. Stephen LeBlanc, UMMC assistant professor of allergy, asthma and clinical immunology. “If you can’t tolerate penicillin, that means there is a whole host of antibiotics you also may not tolerate. Which means there is a whole host of infections that will be treated with second-line drugs.”

In general, those B Team backups cost more, have more side effects or aren’t as effective, LeBlanc said.

“Before surgery, different derivatives of penicillin are administered to patients to reduce the likelihood of wound infections, but if they have an allergy listed on their chart, this doesn’t happen.”

With the substitute drugs, then, there is greater potential for longer hospital stays and other infections, LeBlanc said. Which doesn’t always have to happen.

“If you ask the general population if they are sensitive to penicillin, about 10 percent will say yes,” he said. “They were often told by mom, family or their physician that they should never take it again. If it isn’t investigated, they will avoid it for life.”

No wonder. If you do have an authentic drug allergy, it’s nothing to sneeze at.

“There is a potential danger if people don’t take it seriously, who believe that, because they are older, they are no longer sensitive,” Marshall said. “If they still are, though, at age 72, they may not be able to survive a reaction they survived at age 15.”

Hives, rash and itching may ensue. Worse, there’s the dreaded anaphylaxis, expressed by, among other symptoms, shortness of breath, a rapid but weak pulse, blue skin, swelling under the skin, vomiting, dizziness and fainting. It’s life-threatening.

If, however, you do lose your sensitivity, it could be because your immune system has changed. This happens with age, Marshall said.

“It’s called immune senescence. Your immune system begins to diminish.”

Sadly, that means you are more likely to die from such infections as the flu, for one. It means that you are more likely to get cancer. Happily, it also means your body is less apt to unleash its biological dynamite – that is, overreact to an internal trespasser, making you even sicker: the physiological equivalent of foiling a burglar by blowing up your house.

Marshall said there is another reason that an allergy may go away: abstinence.

“When you have a reaction, this involves something called Immunoglobulin E, or IgE. The ‘E’ is for evil, is what I tell my patients.

“For reasons we don’t know, when certain people are exposed to pollen, certain foods, medications and so forth, their body begins to develop this IgE antibody, which causes an allergic reaction.”

The only treatment is to shun those triggers, he said.

“Apparently, by avoiding exposure long enough, a fair number of people will lose their sensitivity.”

That’s true for children known to be allergic to such edibles as eggs, wheat and soy, LeBlanc said.

“About 80 percent can lose that sensitivity by adulthood,” he said.

There’s also good news for children with nut allergies. For peanuts, which are technically legumes, about 20 percent will lose their allergy in adulthood.

For tree nuts, such as almonds, pecans, walnuts and cashews, the rate is about 10 percent, LeBlanc said. It does matter, though, when an allergy first appears.

“For some foods, including shellfish, the reaction tends to last throughout life, especially if it develops during adulthood,” he said.

A childhood allergy is more likely to disappear later on than one acquired as an adult. Food allergies, though, find you less interesting as a host the older you get, especially by age 40, Marshall said.

“For people in their 60s and older, a food allergy is downright rare.”

Not as rare if you’re a carnivore who gets bitten by a tick. Thanks to a carbohydrate called alpha-gal, some people who have been eating cows, pigs, sheep and other mammals all their lives are suddenly stricken with stomach pain, nausea, headaches, itchy skin, swelling and more after taking on a T-bone.

In the U.S., the only "significant cause" of this setback is the bite of the lone star tick.

“Even then, you can lose your sensitivity if you can avoid meat for an unknown period of time, up to 10 years in some cases,” LeBlanc said. “As for penicillin, about half of those who have an allergy will lose it if they avoid the drug for five years. After 10 years, it’s about 80 percent, but it varies.

“We don’t know the statistics for other drugs that cause allergies. There’s a lot more data on penicillin.”

Then there are people who never lose their penicillin allergy – because they never had one.

“The early penicillin derivatives weren’t as pure as the ones today,” LeBlanc said, “so impure elements may have been the real cause of an allergic reaction.”

And some people say they’re allergic to penicillin because it gives them diarrhea, Marshall said.

“But that’s a common side effect of all antibiotics.”

Because your well-being may be at stake, confirming or refuting a penicillin allergy in particular may be worth it for you. During the last decade or so, there has been a push to question an alleged allergy, LeBlanc said.

“We want to get it off the patient’s chart if it shouldn’t be there.”

This happens in stages, Marshall said. It starts with a patient history, a series of questions whose answers tell the provider if a reaction is real.

Next, an allergist can usually do a skin test. If a red, itchy bump appears on your skin after penicillin is applied, you are probably allergic. On the other hand, LeBlanc said, “a negative result is usually followed by a challenge to the drug to demonstrate tolerance definitively.”

If it’s safe to do so, the allergist administers several doses of the drug, with ever-increasing strengths. If you’re reaction-less after the strongest, you’re in the clear.

“We don’t do a challenge unless there is a good reason to do so,” Marshall said. “The potential benefit must be worth the risk.”

There are cases, though, when patients must take penicillin, even when they’re allergic.

“That’s when nothing else will work,” LeBlanc said. “One of those times is when syphilis is present during a pregnancy. That’s when you do a desensitization.”

A desensitization starts with small doses of penicillin.

“We increase them over short periods of time,” Marshall said, “until the body doesn’t respond to it anymore. But this is only temporary; after completing the medications, the patient will go back to being sensitive.”

While many people mistakenly believe they have an allergy, it’s also clear that more and more of us are becoming susceptible to one thing or the other.

“Something has changed in our environment,” Marshall said. “It’s becoming more allergic – there’s more pollution. And we don’t get out and get as much fresh air as we used to. We have more stress. The overall prevalence of allergic disease in the U.S. is almost 40 percent.

“And more and more people are becoming allergic as they get older. Thirty-five years ago, it was very uncommon to have to test older people. It was considered unethical, especially for people in their 70s or older because of the risks. But now, 10 to 20 percent of older people will have a positive allergic response, which is far more than it was 30 years ago.”

Because that response may involve penicillin, it’s important to know that many alternate drugs do work as well as that wonder drug, Marshall said.

“But penicillin is a fundamentally important antibiotic as a class. A lot of health care providers use it to treat a variety of infections. If you take it out as an option, at the very least, the cost of treatment goes up.

“There is a safety risk and a public health risk when people are led to believe they are allergic to penicillin and all of them are not.”

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