After a antibiotic treatmentsome people see appearing patches or pimples on their skin and, therefore, think they are allergic.
Eight times out of ten, this is false, says Professor Pascal Demoly, a pneumo-allergist at the Montpellier University Hospital. The rash is often linked to the infection itself and not to the medication.
True allergies to antibiotics remain rare. Among suspected cases, only 17% of adults and 9% of children are confirmed by allergy tests.
What are the symptoms of an antibiotic allergy?
It manifests itself in different ways: from the hives outbreak (itchy red patches) to bronchospasm with breathing difficulties. When several organs are affected, it is theanaphylaxis with swelling of the throat (Quincke's edema) and, sometimes, a drop in blood pressure (anaphylactic shock). “Among deaths due to anaphylaxis, the drug cause is the most frequent,” notes Professor Demoly.
Allergic reaction to an antibiotic: how long after taking it?
There allergic reaction may occur within an hour of taking the medication or a few days after taking it. In some delayed severe forms, the skin becomes necrotic (Lyell syndrome, Stevens-Johnson syndrome, etc.). These serious forms are, fortunately, rare, of the order of 1 to 3 cases per million per year.
Penicillins (amoxicillin, etc.) top the list of allergies
Among the classes of potentially allergenic antibiotics:
- The family of penicillins (amoxicillinClamoxyl, Augmentin…) comes first;
- Followed by quinolones (ciprofloxacinCiflox, levofloxacin, etc.);
Allergy to macrolides (whoseazithromycin currently being tested against Covid-19) is rarer. When you are allergic to one of these products, it is exceptional to be allergic to the whole family.
How do you know if you are having an allergic reaction to an antibiotic medicine?
The diagnosis is based primarily on a skin testIn practice, an extract of the suspected antibiotic is placed on the patient's skin. If the skin reacts, the allergy is confirmed.
If the test remains negative, the hypothesis of an allergy is not ruled out. A second test, called “provocation”, is practiced. The antibiotic extract is then absorbed orally, in progressive stages, under hospital supervision.
Two thirds of people allergic to antibiotics react to the skin test, one third to the provocation test. This is why to establish a diagnosis, both tests must be carried out, in this order. Pr Pascal Demoly, pneumo-allergologist at the Montpellier University Hospital
The allergist advises anyone who thinks they are allergic to an antibiotic to dispel any doubt by carrying out these tests. To do this, simply contact your GP or a private allergist. They will be able to refer you to a specialist hospital unit. “It is important to check that the person is really allergic to an antibiotic because alternative solutions are sometimes more toxic and can induce resistance,” he stresses.
Antibiotic allergy: what to do? What treatment?
A desensitization treatment is possible in certain special cases, especially when the patient cannot do without the antibiotic to which he is allergic and there is no alternative solution. This is the case, for example, of children with cystic fibrosis or pregnant women suffering from syphilis, for whom penicillin is essential.
Desensitization involves gradually accustom the body to the allergen so that he doesn't reject it anymore.
Over the course of a day, a dozen doses of antibiotics are administered to the patient, starting with an infinitesimal amount and gradually increasing exposure. Desensitization is effective, but it must be repeated before each course of the offending antibiotic.