Penicillin allergy checklist

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Is a patient allergic to penicillin?

This guide will help pharmacists and other healthcare professionals to diagnose if a patient is allergic to penicillin or not.

Go to the Checklist

The scale of the problem

• A 2019 study in England reported 5.9% of patients have a penicillin allergy recorded on their health record¹
• However, fewer than 10% of these patients are likely to have a true allergy to penicillin²
• In a 2014 US study, penicillin-allergic hospital patients were found to have 23.4% more C. difficile and 14.1% more MRSA infections than expected compared with control subjects³
• This means that up to four million people across the UK may have an incorrect allergy status record, putting them at increased risk of harm.

What is a true penicillin allergy?

• Anaphylactic reactions to penicillin are mediated by IgE⁴
• Rashes that involve hives (raised, intensely itchy spots that come and go over hours) or occur with other allergic symptoms like wheezing or swelling of the skin or throat suggest an IgE-mediated allergy⁵
• Rashes that are flat, blotchy, and spread over days but do not change by the hour are less likely to represent a dangerous allergy⁵
• Fatal anaphylaxis in patients treated with penicillin is rare: approximately 1 in 100,000 for parenteral exposure and 1 in 200,000 for oral exposure^{6, 7}
• Many people report an allergy, when they have actually experienced non-allergy adverse effects such as nausea, diarrhoea, or thrush.

What are the risks of a penicillin allergy?

• For patients with a true Type 1 IgE mediated penicillin allergy, another (non-beta-lactam) antibiotic should be used for treatment⁸
• The risk of cross-sensitivity to other beta-lactam antibiotics varies considerably, depending on the reaction to the index penicillin and the structure of the non-penicillin beta-lactam antibiotic⁴
• The lowest rate of anaphylaxis is for oral penicillins, with a UK study reporting one case of fatal anaphylaxis from oral amoxicillin in 35 years and 100 million treatment courses⁹
• In a 2019 US study involving 11.1 million patients, a recorded penicillin allergy was associated with a 14% increased risk of death¹⁰
• Once a penicillin allergy is recorded, patients receive less effective and/or more toxic antibiotics for subsequent infections^{11, 12}
• Hospitalized patients with documented beta-lactam allergies are more likely to experience inferior outcomes, treatment failures, adverse events, and healthcare-associated infections⁷
• In patients diagnosed with bacterial pneumonia, a penicillin allergy label is associated with an 11% increase in ICU admission and 8% increase in mortality compared to patients without a penicillin allergy label¹³
• Patients with a penicillin allergy record were six times more likely to be prescribed meropenem than patients without a penicillin allergy record, increasing the selection pressure for the emergence and spread of multiresistant bacteria¹⁴
• Most alternatives to penicillins, such as clarithromycin, doxycycline, fluoroquinolones, and linezolid have more extensive adverse effect profiles than penicillins
• More healthcare associated infections: alternatives to penicillins tend to be broader-spectrum antibiotics. This both increases the risk of multi-drug resistance developing and causes increased collateral damage to the microbiota of the skin and intestines, associated with higher rates of MRSA carriage and Clostridioides difficile infection in patients with a penicillin allergy label.^{15, 16, 17}