A large proportion of people who believe they are allergic to penicillin, belonging to one of the most used families of antibiotics, beta-lactams, are ultimately not. For the 90% unfairly labeled “allergic”, this is not a detail: the resulting therapeutic exclusions increase the risk of infectious complications.
True allergies to penicillin and its beta-lactam derivatives are very rare but can be very severe. They do not depend on the dose of the antibiotic and are completely unpredictable. Some patients then present with edema of the face and mucous membranes, anaphylactic shock or drug addiction (a generalized skin reaction which can range from simple rashes to serious damage with peeling of the skin or organ damage). In these cases, after emergency treatment, the patient must be referred to a team specializing in drug allergies. Beta-lactams should not be prescribed subsequently, and this contraindication must be clearly mentioned in their medical file.
Only 10% of people said to be “allergic to penicillin” have a confirmed allergy!
Around 5 to 15% of people in developed countries are allergic to beta-lactams. This family, among the most used, then becomes banned… for life! However, several studies have shown that less than 10% of people who declare themselves or are labeled “allergic” actually are. Out of 100 people claiming to be allergic to penicillin, only 10 have a genuine allergy.
Why are so many people supposedly “allergic to penicillin”? This overvaluation can be explained by several reasons. According to Professor Annick Barbaud, head of the dermatology and allergology department at Tenon hospital (Paris), on the occasion of the Paris Dermatological Days (02-06/12/25), “In young children, a viral infection can cause a rash when taking penicillin antibiotics, such as amoxicillin. The doctor then sometimes notes ‘Allergy to penicillin’ in the health record.“. In adults, “certain side effects of antibiotics (nausea, vomiting, diarrhea or mycoses) can be confused with an allergy, when it is simply a question of digestive or skin tolerance, without contraindication, continues the specialist. Finally, “some people are assigned this allergy due to family history, although no genetic transmission exists for this type of reaction“.
How to know?
How can we distinguish people who are truly allergic to penicillin from those who are not? International recommendations recommend removing the often erroneous label of beta-lactam allergy through a thorough questioning and, if necessary, an allergological assessment to confirm or invalidate the diagnosis. The European Society of Allergology and Clinical Immunology has thus defined different approaches to remove this label when it is unjustified, with an algorithm intended to guide practitioners using several tools.
The doctor begins by asking the patient about the context of the allergy notification:
- If the patient reports digestive symptoms or fungal infections, or mentions a family allergy without a direct link to their own experience, the label must be removed;
- In the event of clinical signs suggesting an allergy after treatment with beta-lactams, the file must be analyzed: type of symptoms, intensity and duration. Simple small red patches lasting a few days (called “acute exanthema”) do not require allergy tests and the antibiotic can be readministered under supervision;
- If a rash occurred in childhood after taking penicillin, the file must be reviewed with the pediatrician to clarify the situation.
- In the event of more severe clinical signs after antibiotic treatment, allergological tests are carried out. They are mainly cutaneous because they allow detection of sensitization to beta-lactams. In children, these tests must be carried out quickly after the suspected allergic accident.
If the results are negative, it is possible to reintroduce the drug in question, first in a hospital setting. Certain scores help determine whether such reintroduction is appropriate. They take into account the age of the accident (the more time passes in the child, the more difficult it becomes to confirm a true allergy), the type of reaction (simple exanthema, rash, edema, anaphylactic shock, serious drug addiction) and the possible need for treatment or hospitalization to manage the accident.
A mistake with serious consequences
The question of whether this is a true penicillin allergy is very important. Indeed, having to do without this therapeutic class increases the risk of infection of the surgical site after a surgical procedure, because prevention by antibiotic therapy (or antibiotic prophylaxis) is not carried out. And in the event of a common infection, the inability to use penicillins lengthens the length of hospitalization and increases the cost of treatment, with alternatives being more expensive without being more effective.
In the event of infection in a patient truly allergic to penicillin, it is then necessary to determine whether the allergy concerns all beta-lactams. Because a true allergy to penicillin does not systematically lead to an allergy to all the other antibiotics in this family. Thus, the risk of “cross” allergy, for example to a cephalosporin of 3e generation remains very low, around 1%. This cephalosporin can therefore be prescribed, but under supervision, ideally for the first administration in hospital.
