Overview of antimicrobial hypersensitivity

It is common for patients to report a history of allergy to an antimicrobial – usually penicillin – and this can present a clinical dilemma. If this antimicrobial is administered to an allergic patient, a severe reaction can occur; however, it is known that many patients who report an allergy tolerate the drug if it is administered again. A history of antimicrobial allergy often dates back to a childhood reaction commonly described as a rash, with vague features not typical of an immediate immune-mediated (IgE) hypersensitivity reaction. In fact, few childhood reactions are reproducible in adulthood, and over 90% of reported penicillin allergies can be excluded by skin testing and oral provocationBourke, 2015Caubet, 2011Vezir, 2016.

Note: Over 90% of reported penicillin allergies can be excluded by antibiotic allergy testing.

Careful assessment and confirmation of antimicrobial hypersensitivity ensures that patients with serious infections are not unnecessarily denied the most effective treatment or treated unnecessarily with broad-spectrum antibiotics. Recent studies (including Australian data) found that when an antimicrobial allergy was recorded on a medication chart, patients were more likely to receive inappropriate antibiotic therapy and have inferior clinical and microbiological outcomesBlumenthal, 2018Bourke, 2015Knezevic, 2016Trubiano, 2016van Dijk, 2016; a significant increase in narrow-spectrum penicillin use and appropriate antibiotics has been reported when a documented antibiotic allergy is removedChua, 2021Trubiano, 2017. Similar impacts are also seen when ‘sulfur’ allergies are removed after testing or reconciliation, especially in patients with immune compromiseUrbancic, 2018.

Accurate and detailed information about antimicrobial hypersensitivity must be documented in the patient’s medical record. If a reported allergy is subsequently excluded, update the medical record and, to avoid relabelling, include information about how the allergy has been excluded.

Note: If a reported allergy is subsequently excluded, update the patient’s medical record accordingly.

Advise patients to wear a medical alert bracelet or necklace if they have a confirmed severe immediate hypersensitivity reaction (eg anaphylaxis, compromised airway, airway angioedema, hypotension, collapse) or delayed hypersensitivity reaction (eg drug rash with eosinophilia and systemic symptoms [DRESS], Stevens–Johnson syndrome / toxic epidermal necrolysis [SJS/TEN], severe blistering or desquamative rash, significant internal organ involvement).

For information on anaphylaxis, see Anaphylaxis.

Common misconceptions about antimicrobial allergy are clarified in Common misconceptions about antimicrobial allergy.

Figure 1. Common misconceptions about antimicrobial allergy

Misconception: Antimicrobial allergy is lifelong.

Antimicrobial allergy is likely to wane over time and many people who report an allergic reaction in childhood can tolerate the drug as an adult.

Misconception: All childhood rashes associated with beta-lactam antibiotics are due to allergy.

Childhood rashes are commonly caused by a viral infection or a drug–virus interaction, rather than drug allergy, and are often not reproducible upon a supervised challenge when the patient is well.

Misconception: Documented antimicrobial allergies are always true allergies.

In an Australian review of antimicrobial prescribing, up to 20% of documented ‘allergies’ were predictable non–immune-mediated adverse reactions (eg gastrointestinal intolerance) and could be removed without testingChua, 2021Knezevic, 2016Trubiano, 2017.

Misconception: Cephalosporin cross-reactivity in patients allergic to penicillin is around 10%.

Only 1 to 2% of patients with a confirmed penicillin allergy have a cephalosporin allergy (see Cross-reactivity between penicillins and cephalosporins).