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A Patient's Guide to Penicillin Allergy

Published on Feb 26, 2019 and last reviewed on Jul 26, 2022   -  4 min read


Taking Penicillin may trigger IgE response in a few individuals resulting in allergic reactions like itching and hives. Read this article to know more.

A Patient's Guide to Penicillin Allergy


Penicillin antibiotics are one of the most frequently prescribed drugs. They are the preferred antibiotics for many infections because of their high efficacy, low cost, and good safety profile. Up to 25 % of patients report an allergy to at least one antibiotic. Penicillin is the most commonly reported drug allergy and likely the most inaccurately reported. Only 1 % of the general population is actually allergic to Penicillin while 10 % claim to be allergic, and 5 to 20 % of hospitalized patients are labeled as Penicillin allergic.

Only about 10 % with reported Penicillin allergy are truly allergic, and over 90 % will tolerate Penicillin after appropriate clinical evaluation. Penicillin allergy is often diagnosed early in life and persists in the patient's medical record for decades. Most allergy labels are probably assigned in primary care, as the majority of antibiotics are prescribed in primary care. Over 50 % of allergies may not be immunologic in origin, meaning that they are not true allergies from a medical standpoint.

What Types of Allergic Reactions Can Occur?

It is important to distinguish a side effect from an allergy.

From a medical standpoint, an allergy is more important to know about, but also tell your healthcare provider about any side effects you have experienced in the past. Just because one has experienced a side effect or allergy to a drug, it does not always mean it will happen again if they take it.

Why Are Penicillin Allergies Misdiagnosed?

Attributing a reaction to a drug can be difficult because there may be other factors involved that could have caused the reaction, but were overlooked. For example, in children who have mistakenly been prescribed Amoxicillin for mononucleosis, a rash may develop, not because of an allergy, but because mononucleosis itself leads to a rash.

Patient recall error can also lead to misdiagnosis, especially if the reaction was remote. Sometimes patients and clinicians call it an allergy, but it may be just a side effect, such as nausea. Allergies are often not verified or excluded by diagnostic testing. In one study, only 4 % of medical records have documentation detailing specific allergic reactions. Approximately 50 % and 80 % of patients with a true Penicillin allergy lose their sensitivity at five and ten years respectively, after their last reaction. Therefore, if a particular person has not had a reaction for many years, then it is very likely that they are no longer allergic anymore.

Why Should One Care About Penicillin Allergy?

The research has shown that if one has a false Penicillin allergy label, they are more likely to have treatment failure and complications when they are being treated for an infection. Doctors will prescribe antibiotics that may be less effective, more toxic, and more expensive. Therefore, if one thinks they have a Penicillin allergy, get a proper evaluation. Telling their doctor that they have a Penicillin allergy, when they actually do not, only hurts them.

Can an Individual Take Other Antibiotics That Are Similar to Penicillins?

Some of the best antibiotics are closely related to Penicillin. Amoxicillin, Ampicillin, and Piperacillin are like brothers or sisters of Penicillin, Cephalosporins such as Cephalexin, Cefuroxime, and Cefixime are like first cousins, and Carbapenems such as Ertapenem, Meropenem, and Imipenem are like second cousins. They all share a similar chemical structure, but as the drug becomes less related to Penicillin, it becomes more unlikely that they will have a reaction. Even if they have a true and severe allergic reaction to Penicillin, it is very unlikely that they will have an allergic reaction to its cousins.

How Does Someone Know They Are Allergic to Penicillin?

It is important to have a discussion with your healthcare provider to determine if they truly have an allergy to penicillin. The doctor will question the respective person to assess their risk of having a reaction to penicillin. Some examples are below:

If the history is unclear, they may be referred to an allergist to have a skin test done. If the skin test is negative, then they may receive an oral challenge of penicillin. If they have no reaction to the oral challenge, then they do not have an allergy to Penicillin. In most situations, they can bypass the skin test and go straight to the oral challenge if they are at low risk of having a reaction.

What if One Tests Positive for Penicillin Allergy?

The allergic ones can still safely take the cousins of Penicillins. If your reaction is minor (mild rash), then they can still take Penicillin if your doctor thinks it is the best antibiotic for their infection. Minor reactions can often be controlled with antihistamines such as Diphenhydramine. If they show reactions that are severe (throat closing, tongue swelling, low blood pressure), then it is best to avoid that drug completely and consider obtaining a medical alert bracelet engraved with that allergy.

What if One Tests Negative for Penicillin Allergy?

They can safely take any Penicillin antibiotics. It is important to always inform their existing and new healthcare providers that they are not allergic to Penicillin anymore because the label might still be in their medical records. Remember, that individual may have had this allergy label for many years, so all their medical records during that time period will likely have outdated information.


Penicillin allergy is a common condition. Thus, everyone should take an effort to get tested for Penicillin allergy as it can result in adverse reactions. If allergic to Penicillin, it is important to inform the doctors during consultation and be mentioned in all the medical files for future reference.


Frequently Asked Questions


What Happens if You Are Allergic to Penicillin?

If you are allergic to Penicillin, you will have rashes, itching, and hives. You might also note the following symptoms.
- Swelling.
- Fever.
- Wheezing.
- Shortness of breath.
- Runny nose.
- Anaphylaxis.
- Watery eyes.


What Drugs Should You Avoid if You Have Penicillin Allergy?

You should avoid the following drugs, if you have a Penicillin allergy.
- Amoxicillin-clavulanate.
- Amoxicillin.
- Ampicillin.
- Nafcillin.
- Piperacillin-Tazobactam.
- Dicloxacillin.


How Can You Develop a Penicillin Allergy?

An allergic reaction to Penicillin happens when the body overreacts to the drug. The body's normal response does not happen as the drug is considered a harmful substance for the body. The person had to be exposed at least once to get the Penicillin allergy.


Is Penicillin Allergy Hereditary?

There is no evidence to show that Penicillin allergy is hereditary. If you have a family member who is allergic to Penicillin, you can take a precautionary test. This will help you to overcome severe allergic reactions.


What Antibiotics Can I Take if I Am Allergic to Penicillin?

The following antibiotic drugs can be taken if you are allergic to Penicillin.
- Quinolones like Ciprofloxacin.
- Tetracyclines like Doxycycline.
- Aminoglycosides like Gentamicin.
- Macrolides like Clarithromycin.
- Glycopeptides like Vancomycin.


How Do I Know if I Am Allergic to Penicillin?

You can identify whether you have a Penicillin allergy or not with the help of the following symptoms.
- Hives.
- Skin rash.
- Fever.
- Itching.
- Swelling.
- Wheezing.
- Shortness of breath.
- Runny nose.
- Anaphylaxis.
- Itchy and watery eyes.


Does Penicillin Allergy Go Away?

Allergy to Penicillin is known to go away after a period of time. Medical reports suggest that nearly 20 percent of the people are known to be allergic to Penicillin for a prolonged period of time.


What Foods Are High in Penicillin?

Penicillin is high in the following foods.
- Wheat.
- Corn.
- Flour.
- Barley.
- Walnuts.


How Does Penicillin Allergy Rash Look?

The allergic reaction to Penicillin begins as a red spot in the body. It starts covering a large area of the skin. These reactions often occur within a few hours of taking the drugs. You should inform your doctor if you have a Penicillin allergy.


What Should You Not Take With Penicillin?

The following drugs should not be taken with Penicillin.
- Birth control pills.
- BCG.
- Cholera vaccine.
- Chloramphenicol.
- Erythromycin.
- Methotrexate.
- Fusidic acid.
- Mycophenolate.


How Do You Treat the Allergic Reaction to Penicillin?

The most common methods that are adapted for overcoming an allergic reaction are:
- Withdrawal of the drug. If you have a penicillin allergy, then the drug must be withdrawn as soon as possible.
- Antihistamines.
- Corticosteroids.
- Treatment should be given for an anaphylaxis reaction.


How Common Is Penicillin Allergy?

Medical reports suggest that ten percent of the American population are suffering from Penicillin allergy. It might vary according to the geographic population.


How Long Does a Penicillin Allergy Last?

The allergy to Penicillin usually goes away if a person avoids the drug for approximately ten years. It is necessary to get tested for Penicillin allergy after ten years. Penicillin allergy can happen within 30 minutes of administration of the drug. It can even occur a few hours or days later in some patients.


How Do You Test for Penicillin Allergy?

The testing for Penicillin allergy requires a skin test. An intradermal test is conducted that would involve a skin prick. It can indicate whether a test is positive or negative for Penicillin allergy. If the involved site of the examination does not have any changes, then the test would be concluded as negative.


What Foods Are Least Likely to Cause Allergic Reactions?

The following foods are least likely to cause allergic reactions.
- Lentils.
- Quinoa.
- Avocado.
- Sweet potato.
- Rice milk.
- Dulse.
- Figs.
- Salba seeds.

Article Resources

Last reviewed at:
26 Jul 2022  -  4 min read




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