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Allergic to Penicillin? Which antibiotics can you take?

Medically reviewed by Sally Chao, MD. Last updated on July 5, 2021.

Official answer

by Drugs.com

If you think you have a penicillin allergy, chances are you probably don't. More than 90 percent of people who believe they are allergic to penicillin really aren't. It's also very likely that you have outgrown an allergy to penicillin, especially if the reaction happened more than 10 years ago. For a true allergy, there are other classes of antibiotics that you can take.

Penicillin was discovered in 1828. Today, the family of penicillin drugs includes more than 15 different antibiotics, such as:

These antibiotics can be given by mouth or injection to treat many types of bacterial infections. Amoxicillin, for example, is one of the most common oral penicillins. It is often the first choice to treat infections of the ear, nose, throat, lungs, sinuses and urinary tract.

How common is penicillin allergy?

According to the Centers for Disease Control and Prevention, less than 1 percent of people have a true penicillin allergy, even though about 10 percent of people tell their doctors they are allergic to penicillin.

Sometimes, a common reaction to penicillin (such as an upset stomach or diarrhea) is mistaken for an allergy. In other cases, a person may report a family history of penicillin allergy, but penicillin allergy is not passed down through families.

What are the signs of a penicillin allergic reaction?

You may have had an allergic reaction to penicillin if you:

  • Had the reaction within one hour of taking penicillin
  • Developed raised and itchy skin patches (hives)
  • Had swelling of your face, throat, hands or feet (angioedema)
  • Had wheezing, chest tightness or difficulty breathing
  • Had nausea and vomiting or diarrhea
  • Had sudden dizziness, weakness or loss of consciousness

Why not just avoid penicillin?

It is important to know for sure whether you are allergic to penicillin. Sometimes penicillin is the best drug to treat a certain infection. Using other drugs—called broad-spectrum antibiotics—instead of penicillin can be more expensive and less effective. These drugs are also more likely to cause antibiotic resistance and result in an infection that is very hard to treat.

Using a broad-spectrum antibiotic for an infection like strep throat (which responds quickly to penicillin) also increases the risk of developing a serious antibiotic-related condition. For example, the risk of a condition called methicillin-resistant Staphylococcus aureus (MRSA) is more than 50 percent higher. There is also a much higher (35 percent) risk of developing an intestinal infection called Clostridium difficile (C. diff). These infections are both serious and hard to treat.

What if you have a penicillin allergy and you need antibiotics?

If you have a true penicillin allergy, you should not take any antibiotics in the penicillin family. Not all bacterial infections are treated with penicillin, but if you have an infection that is usually treated by penicillin, you may be able to take a drug that is similar to penicillin called a cephalosporin. Over 95 percent of people with penicillin allergy can safely take cephalosporins, which are a bit structurally different from penicillins. There are also many broad-spectrum antibiotics that can be used in place of penicillin.

If you have a serious infection that is best treated by penicillin, it's also possible to have emergency desensitization treatment. This means you are given small doses of penicillin every 15 minutes over four hours. This will allow you to be treated safely with a large penicillin dose. This type of desensitization wears off, but it can be followed by allergy shots from an allergist that will give you long-lasting protection.

There are very few cases in which allergy testing or desensitization for penicillin is dangerous. These cases are called severe hypersensitivity syndromes. They are rare, but they include these syndromes:

  • Drug rash with eosinophilia and systemic syndrome (DRESS)
  • Stevens-Johnson syndrome
  • Serum sickness
  • Toxic epidermal necrolysis
  • Hemolytic anemia
  • Acute interstitial nephritis

Talking to your doctor

If you have had any signs of a penicillin allergy, or if you suspect a penicillin allergy for any other reason, talk to your doctor before you need an antibiotic. It will be important to let your doctor know what medication you were taking when you had a reaction and what the symptoms were. Your doctor will also ask how the reaction was treated and how long ago it happened. Based on these factors, you and your doctor can decide whether you should have testing for a penicillin allergy.

Skin testing at a doctor's office is the best way to find out for sure whether you are allergic to penicillin. You may be sent to an allergist for testing. Skin testing can be done on your back or your arm. It may be a tiny injection under your skin or a small scratch. If the test is positive, you may have some local swelling and itching, but this reaction will go away within an hour or so.

If you don't have a skin reaction to penicillin, there is a 95 percent chance you are not allergic. Your doctor will then do an oral challenge. That means you will get a dose of penicillin and be observed in the office. If you don't have a reaction to the oral challenge or the skin testing, there is almost a 100 percent chance you are not allergic.

Serious reactions to skin testing or an oral challenge are rare. Doctors who do this type of testing are prepared to manage any serious reaction.

Finding out you are not allergic to penicillin could mean better and safer treatment for you in the future. Tell any new health care provider about your allergy. You may also want to wear a penicillin allergy alert bracelet.

References
  1. McCullagh DJ, Chu DK. Penicillin allergy. Canadian Medical Association Journal. 2019 Feb 25;191(8):E231. https://dx.doi.org/10.1503%2Fcmaj.181117.
  2. Centers for Disease Control and Prevention (CDC). Evaluation and diagnosis of penicillin allergy for healthcare professionals. October 2017. Available at: https://www.cdc.gov/antibiotic-use/clinicians/Penicillin-Allergy.html. [Accessed May 31, 2021].
  3. StatPearls. Amoxicillin. August 2020. Available at: https://www.ncbi.nlm.nih.gov/books/NBK482250/. [Accessed May 31, 2021].
  4. American Academy of Allergy Asthma & Immunology (AAAAI). Penicillin allergy FAQ. September 2020. Available at: https://www.aaaai.org/Tools-for-the-Public/Conditions-Library/Allergies/Penicillin-Allergy-FAQ. [Accessed May 31, 2021].

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