Penicillin Allergy

Penicillin is an antibiotic originated from the Penicillium fungus, which belongs to the group of β-lactam antibiotics. There are different types of penicillins, but they all have a β-lactam nucleus.

Despite being very effective in fighting bacteria, some patients may have an allergy to penicillin. The classification of these allergies is based on the time interval between drug administration and the onset of the reaction. What else should you know about the topic?

Each type of penicillin acts against bacteria to different degrees. In addition to eliminating bacteria that cause different infections in our body, penicillin serves to prevent infections caused by gram-positive bacteria.

What happens if we are allergic to penicillin?

Allergy to beta-lactams is often related to morbidity and mortality. The diagnosis of penicillin allergy is made through medical history and skin tests.

Controlling the patient who is allergic to penicillin

The diagnosis of penicillin allergy is made through skin tests and analyzing the patient’s clinical history. Also, it should be considered that there are several types of allergic reactions.

Types of Allergic Reactions

The classification of allergic reactions to penicillin and, in general, to beta-lactam antibiotics is based on the time interval between administration of the drug and the onset of the reaction.

immediate allergic reactions

Are those reactions that occur within the first hour after administration of the drug. They are usually mediated by specific immunoglobulin E (IgE), which releases histamine and other inflammatory mediators very quickly.

How it manifests varies from mild reactions such as urticaria, angioedema and wheezing, to severe reactions such as anaphylactic shock.

Accelerated reactions

This type of reaction appears between two and seventy-two hours after antibiotic administration. Although its mechanism is not well described, reactions such as urticaria, angioedema, laryngeal edema and wheezing may occur.

Delayed Allergic Reactions

They are those that occur from seventy-two hours after the administration of the drug. They are usually mediated by T lymphocytes and manifest in very different ways.

Both accelerated and late reactions can be categorized as non-immediate reactions. Signs and symptoms of non-immediate reactions include the following:

Maculopapular or fixed drug eruption.
Urticaria.
Multiform erythema.
Stevens-Johnson syndrome.
Toxic epidermal necrolysis.
Exfoliative or contact dermatitis.
Hypersensitivity syndrome.
Lichenoid dermatosis.

However, on the positive side, the most common reactions are usually not serious and consist of maculopapular rash followed by urticaria.

How is a penicillin allergy diagnosed?

Allergy testing is essential if a penicillin allergy is suspected.

If hypersensitivity is suspected, penicillin allergy testing is essential. This is important as adverse reactions are often confused with allergic reactions.

The diagnosis is made based on the description of symptoms and the time elapsed between the ingestion of penicillin and the onset of the reaction, as well as the type of symptom.

Thus, the type of allergic reaction can be classified as immediate or non-immediate. In immediate allergic reactions, it has been found that the longer the time elapses between the initial reaction and the study, the less chance of a positive skin test result.

However, this loss of sensitivity will not necessarily be permanent. There is a possibility that the patient will be sensitized with these antibiotics after performing skin tests or after administering the drug again. On the other hand , in non-immediate reactions, the phenomenon of loss of sensitivity is not common.

Skin tests to diagnose penicillin allergy

For immediate reactions, a skin allergy skin test, also called a prick test or prick test , is first performed . One or more allergens can be used, and if the answer is negative, the next step is to perform an intradermal test.

Both are usually done on the forearm and the reading takes place after 15 to 20 minutes. However, in non-immediate reactions, intradermal tests can be started directly with readings in 20 minutes and in 48 and 72 hours.

During the performance of intradermal tests, systemic reactions may occur. This can happen if you use many substances at the same time.

desensitization

During desensitization, the antibiotic is administered again so that the therapeutic dose can be determined.

Desensitization consists of re-administering the antibiotic that caused an allergic reaction in progressive doses until reaching the therapeutic dose.

Desensitization is reversible and depends on the continued presence of the antibiotic in the body. However, it loses its effectiveness when the administration is suspended for a period of more than 48 hours.

Conclusion

The penicillin group of antibiotics is very frequently prescribed and, therefore, in sensitized people, allergic reactions that can be fatal occur.

Therefore, it is important to properly and timely diagnose true antibiotic allergies and differentiate them from pseudo-allergic reactions.