With over 15 million prescriptions written yearly, amoxicillin is the most commonly prescribed antibiotic in the United States. While it is generally considered safe and effective, approximately 10% of the population is “labeled” as having an amoxicillin allergy. However, this estimate is considered high. It’s been found that 90-95% of people who are thought to be allergic can tolerate amoxicillin after seeing an allergist to get an allergy test. A true penicillin allergy (which can lead to death) is rare, with the estimated frequency of anaphylaxis at 1-5 per 10,000 cases of penicillin therapy.
Most amoxicillin allergies are associated with childhood. One of the more common adverse drug reactions is a rash, ranging from urticarial-like pruritic rash (hives) to maculopapular rash. In this article, we will explore the causes and symptoms of an amoxicillin-induced rash, view photos of two types of an amoxicillin rash, and provide guidance on identifying and managing it.
FUN FACT: Approximately 50 percent of people will outgrow a penicillin allergy within five years, and 80 percent will outgrow it within 10 years. (MayoClinic)
A quick history of amoxicillin
Penicillin was accidentally discovered in the 1920s by Dr. Alexander Fleming (labeled “father of amoxicillin"). Returning from vacation, he noticed that the mold growing on a Petri dish inhibited the growth of Staphylococcus bacteria. Ureka! Up until now, minor cuts could be a death sentence for people.
Sadly, the science community wasn’t very interested and it was another 10 years before the “Penicillin Project” was started just in time to save countless lives during WWII. By the mid-1940s, the age of antibiotics had begun, but so did antibiotic resistance.
By the late 1950s, amoxicillin had been created to battle antibiotic resistance. Adding an extra amino group to penicillin resulted in a broader range of coverage against bacteria than penicillin alone offered.
Allergy to amoxicillin: The Misconception
Many adults have grown up believing they are allergic to amoxicillin, but the statistics show otherwise. It’s easy to see why this happens. Let’s review some of the contributing misconceptions…
Misconception #1: The patient was told they had a “reaction” as a young child
Many adults report that they were told they were allergic to amoxicillin (penicillin) because they developed a rash as a child while taking it. The “allergic” rash experienced while taking amoxicillin in many cases is harmless as discussed later in the article. Also, the amoxicillin rash can be a symptom of the viral illness the amoxicillin was thought to be treating. Honest misunderstanding by a parent worried about their child...one could understand.
Misconception #2: Family history of penicillin allergy
The patient reports being told by their parents they are allergic to amoxicillin (penicillin) because it runs in the family. An amoxicillin allergy is not inherited. Let’s repeat this…amoxicillin allergies are not inherited.
Misconception #3: It’s a mystery
An adult was told they were allergic to amoxicillin (penicillin). The patient was a young child with sparse details if any, available.
The risk associated with mislabeling an amoxicillin (penicillin) allergy
According to the MayoClinic, “people who have a penicillin allergy listed in their medical records are more likely to…
- Experience treatment failure due to the use of a second-line antibiotic to treat their infection
- Develop a post-surgical infection due to the use of a second-line prophylactic antibiotic at the time of surgery
- Be treated with a more toxic or expensive antibiotic due to their listed penicillin allergy
- Be more likely to develop an infection with a resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) or Clostridium difficile.”
Amoxicillin (penicillin) allergy testing
An amoxicillin allergy can limit effective treatment options for many infections as it includes the entire class of penicillin known as “cillins” as well as certain drugs in the cephalosporin class of antibiotics. That’s a lot of critical antibiotic treatment options, so confirming or disproving an allergy to penicillin can benefit your health. A negative allergy test can allow for better treatment options, targeted therapy, and potentially better treatment outcomes.
The American Academy of Allergy, Asthma, and Immunology describes the process in the “Penicillin Allergy- what do you need to know?”
Understanding amoxicillin and its uses
What is Amoxicillin?
Amoxicillin is a broad-spectrum oral antibiotic used to treat various bacterial infections. It works by stopping the growth of bacteria and preventing it from reproducing. It is considered first-line treatment in pediatric-age patients for acute otitis media (ear infections), sinusitis (sinus infections), and pharyngitis (strep throat). Also, it can treat many other medical conditions in adults and children. These range from lower respiratory infections to dental abscesses, and it can even help treat stomach ulcers. Due to the broad range of conditions it can treat, knowing if you have an allergy is essential.
Amoxicillin “rash”
Most antibiotics can cause a rash, but amoxicillin causes a rash more frequently than other types of antibiotics. Amoxicillin rashes are thought to occur when the immune system reacts to the medication. It’s important to know that an amoxicillin rash can develop anytime during the course of treatment and can be a sign of an allergy. A person should consult a medical provider if a rash appears after starting amoxicillin.
With that said, not all amoxicillin rashes are created equal. An amoxicillin rash can present in various ways, and its appearance may vary from person to person. It can be mild or severe, depending on how sensitive the individual is to the medication. It can be harmless or potentially deadly. Let’s review some amoxicillin rash photos…
A type-I hypersensitivity reaction involves an IgE-mediated response in sensitized patients, inducing widespread histamine release. This is an allergic reaction to amoxicillin and is concerning. The symptoms of hives are typically as follows:
- intense itching is present
- can appear after only 1-2 doses of amoxicillin
- raised red and/or white bumps (welts or splotches)
- can come and go quickly and change location on the body
- this rash is more concerning for a “true” amoxicillin allergy
*Anyone who develops hives while taking amoxicillin should seek urgent medical advice. If breathing difficulties or swelling of the face/tongue occur alongside the rash, they should call the emergency services for immediate medical help.*
To learn more about hives, go to DermNet https://dermnetnz.org/topics/acute-urticaria
This type-IV hypersensitivity reaction is not mediated by histamine release. The symptoms of a maculopapular (morbilliform) rash are typical as follows:
- No itching to mild itching may be present
- usually appear 3-10 days into taking the amoxicillin
- The rash distribution/pattern is generally on both sides of the body
- pink-to-red flat/slightly raised bumps
- this rash is less concerning for an amoxicillin allergy and begins to fade after stopping the amoxicillin
To learn more about a morbilliform rash, go to DermNet: https://dermnetnz.org/topics/morbilliform-drug-reaction
Fun Fact: Almost all (80% to 100%) patients taking amoxicillin who are actively sick with infectious mononucleosis (also known as “mono” or the “kissing disease”) may develop a maculopapular rash attributed to a type IV–mediated hypersensitivity reaction.
Note: Photos of amoxicillin rashes can be helpful. However, it is important to note that individual reactions to amoxicillin can vary, and not all rashes will look the same. Consulting a healthcare professional is essential for an accurate diagnosis.
Over-the-counter (OTC) and home remedies to help the itch:
Itching can be very uncomfortable. From a little mosquito bite to a full-blown allergic reaction (hives) to amoxicillin. It’s not unusual for a person to scratch their skin until it bleeds to make it stop. Here are a few suggestions to help with the itching caused by an allergic reaction:
- applying a cold, wet cloth
- soaking in a lukewarm oatmeal bath (avoid hot baths as they can make the itching worse)
- stay hydrated
- avoid tight clothing
- avoid overheating/sweating
For additional recommendations, check out “How to Relieve Itchy Skin” from the American Academy of Dermatology.
When to seek medical attention
Rashes can be scary and confusing. Sometimes, a rash might be harmless, but other times it could indicate that you’re allergic to amoxicillin. Allergic reactions can escalate rapidly and pose serious health risks, even becoming life-threatening.
If you suspect you or your child is experiencing a reaction to amoxicillin, please seek medical advice/treatment. Consulting a healthcare professional for an accurate diagnosis and appropriate treatment is crucial. Additionally, seek immediate medical attention if you or your child experiences difficulty breathing, swelling of the face or tongue, or other severe symptoms.
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DISCLAIMER
The information provided on this medical blog is for educational and informational purposes only and is not intended as medical advice. While we strive for accuracy, medical knowledge constantly evolves, and individual health situations vary. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay seeking it because of something you have read on this blog. The authors and publishers of this blog are not responsible for any adverse effects or consequences resulting from using any suggestions, products, or procedures discussed in this blog.
REFERENCES
- https://www.mayoclinic.org/medical-professionals/pediatrics/news/5-common-misperceptions-about-penicillin-allergies/mqc-20440491
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4717649/
- https://www.ncbi.nlm.nih.gov/books/NBK482250/
- https://www.statista.com/statistics/782068/amoxicillin-prescriptions-number-in-the-us/#:~:text
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3255391/
- https://dermnetnz.org/topics/morbilliform-drug-reaction
- https://www.sciencemuseum.org.uk/objects-and-stories/how-was-penicillin-developed
