Makindo Medical Notes

Background

Penicillin allergies are commonly reported, yet true allergic reactions are relatively rare. While about 10% of the population claims to have a penicillin allergy, less than 1% are truly allergic. Mislabelling patients as penicillin-allergic can lead to the use of less effective, more expensive antibiotics with a higher risk of adverse effects and antimicrobial resistance.

• Many patients may have experienced non-immune-mediated reactions such as nausea, vomiting, or exanthems (e.g., rash after taking amoxicillin during an Epstein-Barr virus infection), which are not true allergies.
• Penicillin allergies are not always lifelong. Approximately 50% of individuals lose their sensitivity over five years, and 80% over ten years.
• A reaction to penicillin during childhood is unlikely to indicate a persistent true allergy in adulthood.
• Only 1–2% of patients with a confirmed penicillin allergy are also allergic to cephalosporins. Cephalosporins can be a safe alternative for patients with a low risk of severe allergic reactions.
• Patients with a history of delayed, non-severe reactions (e.g., mild childhood rashes over 10 years ago) may be suitable candidates for an oral rechallenge with low-dose penicillin under medical supervision.
• With appropriate assessment and allergy testing, it may be possible to remove the penicillin allergy label from many patients.
• Allergic reactions to β-lactam antibiotics are the most frequently encountered immunologically mediated adverse drug reactions.
• Patients labeled as penicillin-allergic are more likely to receive alternative antibiotics that are more costly, have broader spectra, and carry higher risks of adverse reactions (including Clostridioides difficile infection) and antimicrobial resistance.

Taking a History of Penicillin Allergy

When assessing a patient with a reported penicillin allergy, consider asking the following questions:

• Previous Reactions: What antibiotics has the patient reacted to in the past?
• Tolerated Antibiotics: What antibiotics has the patient taken and tolerated since the allergy diagnosis, especially penicillins or cephalosporins?
• Timing: When did the reaction occur?
• Nature of Reaction: What were the symptoms (e.g., diarrhoea, rash, swelling, difficulty breathing)?
• Rash Details: If a rash was present, describe its nature (e.g., maculopapular, pustular, bullous, urticarial). Could it be related to an underlying condition (e.g., viral infection) or interaction with other medications?
• Onset After Medication: How long after starting the antibiotic did the reaction appear?
• Purpose of Antibiotic: Why was the patient taking the antibiotic?
• Severity: Did the reaction result in hospitalization or require intensive care?
• Resolution: Did the reaction resolve upon stopping the antibiotic?
• Information Sources: Gather details from the patient, caregivers, general practitioner, and medical records.

Assessment and Management

Understanding the classification of antibiotics and their relation to penicillin is crucial for safe prescribing. Antibiotics are often color-coded to help healthcare providers distinguish between them, especially concerning penicillin allergies.

• Penicillins (Red): These should not be given to patients with a known penicillin allergy.
• Other β-Lactams (Amber): Cephalosporins and carbapenems may be administered with caution to patients with minor penicillin allergies.
• Non-β-Lactam Antibiotics (Green): These can be safely given to penicillin-allergic patients regardless of the nature of the allergy.

The color-coding system aids in quickly identifying suitable antibiotics for patients with penicillin allergies.

References

• Penicillin Allergy: A Practical Guide for Clinicians
• Assessment and Management of a Patient Presenting with a History of Penicillin Allergy
• Penicillin Allergy: A Practical Approach to Assessment and Prescribing