Accurately diagnosing antibiotic allergies

Accurately diagnosing antibiotic allergies

Source: Burger / Phanie / Science Photo Library

Antibiotic allergy testing should take place in a specialist allergy centre to ensure correct interpretation of results and management of the patient if a severe reaction occurs

Drug allergy, as defined by the British Society for Allergy and Clinical Immunology, is an adverse drug reaction with an established immunological mechanism. All forms of natural and semisynthetic penicillins or drugs with a similar structure, such as cephalosporins or carbapenems, can cause allergy. These drugs, which have a beta-lactam ring, are recognised as one of the most frequent causes of immediate (within 1 hour) and delayed (after 72 hours) drug reactions. 

Correct diagnosis can be difficult, but true allergy is more likely if the patient has recognised allergic symptoms (e.g. rash, rash involving hives, wheezing, or swelling of the skin or throat), or has previously experienced a similar reaction to the same agent or another agent in the same class. Gastrointestinal symptoms alone do not represent a true allergy and alternative biological or pharmacological explanation should be excluded before a diagnosis of allergy is made[2].



Adverse reactions to penicillin have been reported in 0.2–5.0% of individuals per course of treatment[3]. However, fewer than 10% of those believed to be allergic to penicillin are truly allergic[2]. As a result, antibiotics can be withheld unnecessarily, affecting clinical outcomes, increasing healthcare costs and potentially contributing to the development of drug-resistant bacteria[3]. Accurate diagnosis and antimicrobial stewardship practices are therefore key[2].

Delabelling — the removal of inappropriate patient allergy labels — allows first-line treatment options to be used. These are often more effective antibiotics with fewer side effects, have a narrower spectrum of activity and are more cost efficient[4]. Using effective narrow-spectrum agents where possible is one of the major aims of antimicrobial stewardship and ensures the right drug is being used for the right patient. Current practice of delabelling allergy status in the UK varies and may depend on whether there is an established local allergy service or whether pharmacists have the capacity to assess patients’ allergies on admission to hospital.

Pharmacists, working as part of the wider multidisciplinary team, are able to effectively manage infections in patients with antibiotic allergies by delabelling their inappropriate allergy status on admission[5] (see Box 1). The process of optimising medication on admission to hospital currently falls under the remit of doctors and pharmacists[6].

This article describes the possible consequences of labelling a patient with an antibiotic allergy; the subsequent impact on patient outcomes; how pharmacists can undertake appropriate investigations and delabel patients; and when to refer patients to specialist allergy services. This article complements a previous article on the identification and management of penicillin allergy[3].

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