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NEED TO KNOW
Penicillin
• The most commonly reported antibiotic allergy , and associated with poor prescribing and patient health outcomes .
• Delabelling is the removal of a patient ’ s self-reported penicillin allergy via allergy testing or medical reconciliation .
Severe cutaneous adverse reactions
• Seek specialist advice immediately if a SCAR is suspected .
NSAID
• NSAID hypersensitivity can involve COX-mediated or allergic mechanisms .
• COX-mediated hypersensitivity will cross-react between medications that inhibit COX-1 , including paracetamol .
• Allergy-mediated hypersensitivity is specific to a single NSAID .
• Aspirin desensitisation can be helpful in NSAID-exacerbated respiratory disease .
Local anaesthetic
• Local anaesthetic allergies are rare .
• History of other agents ( including latex , skin wash , antibiotics ) used at the time of reaction is helpful .
Radiocontrast
• Reactions can occur to iodinated radiocontrast or gadolinium .
• Most reactions can be classed as physiological or allergic ( immediate or delayed ) reactions .
• Prescribe pre-medication to patients with previous allergic reactions to contrast and use an alternative agent ( if possible , an iso-molar agent ).
• Mast cell tryptase testing in the context of an acute contrast reaction is helpful diagnostically .
Dr Michaela Lucas ( left ) Clinical immunologist and immunopathologist , Sir Charles Gairdner Hospital and Perth Children ’ s Hospital , Perth ; Department of Immunology , PathWest Laboratory Medicine ; Medical School , University of Western Australia , Perth , Western Australia ; past president of the Australasian Society of Clinical Immunology and Allergy ( ASCIA ).
Dr Ana Copaescu ( right ) Allergist and immunologist at McGill University , Quebec , Canada ; Centre for Antibiotic Allergy and Research , Infectious Diseases Department , Austin Health , Melbourne ; PhD candidate with the University of Melbourne , Victoria .
Dr Adrian Buzynski ( left ) Paediatrician at Fiona Stanley Hospital ; immunology fellow , Department of Immunology , Perth Children ’ s Hospital , Perth , Western Australia .
Dr Jason Trubiano ( right ) Director of infectious diseases and the Drug and Antibiotic Allergy Service at Austin Health , and head of the Centre for Antibiotic Allergy and Research , Austin Health , Heidelberg ; The National Centre for Infections in Cancer , Peter MacCallum Cancer Centre , Melbourne ; Department of Infectious Diseases , University of Melbourne , at the Peter Doherty Institute for Infection and Immunity , Victoria , Australia .
Common drug allergies
INTRODUCTION
ADVERSE drug reactions ( ADRs ) are common . They are generally described as Type A reactions , predictable side effects of a drug based on its known pharmacological properties ; or Type B reaction , which are unpredictable ‘ idiosyncratic ’ adverse reactions . Type B reactions that are immune-mediated are referred to as drug allergies and , like other allergies , are grouped using the 1963 classification , published by British immunologists Robert Coombs and Philip Gell ( see table 1 ).
The most common types of drug allergies are Type 1 ( immediate and IgE-mediated reactions ) and Type 4 ( T-cell-mediated reactions that manifest as non-immediate delayed reactions ). The clinical presentations of Type 1 and 4 reactions vary based on the cells involved , dose of drug delivered and patient factors . The most severe immediate reaction is life-threatening anaphylaxis , whereas the most severe non-immediate allergic reactions are severe cutaneous adverse drug reactions ( SCAR reactions ). Once a severe T-cell-mediated reaction has occurred and is confirmed , lifelong avoidance of the culprit drug is essential , as people do not outgrow T-cell-mediated allergies . There are reports , however , that some may outgrow IgE-mediated allergies . Advise first-degree family members of patients who experience a SCAR to avoid the eliciting drugs , given the genetic associations of these reactions .
It is important in any drug reaction to capture details of the reaction , as this determines future drug use advice , helps to risk-stratify future testing and aids specialist ’ s triage ( see box 1 ).
Measurement of serum mast cell tryptase ( MCT ) in the acute setting of a drug reaction is helpful , as allergic reactions are sometimes difficult to distinguish from mimics . MCT , a serine protease , is released from mast cells and basophils into serum because of degranulation during an IgE Type 1 reaction . MCT rises steeply up to 90 minutes after the reaction ; to capture the peak of the increase , take serum for MCT testing 2-4 hours after the acute event . The peak of the MCT after the reaction is then compared with baseline
Box 1 . Minimum information to capture for current and drug reactions
• Drug and date prescribed .
• Dose , route , frequency of drug course .
• Reason for prescription ( eg , type of infection ).
• Reaction ( type , duration , management ).
• Concurrent other medication at time of reaction .
serum MCT , which requires a second blood test when the patient is well . A peak MCT should be greater than 1.2 baseline + 2mcg / L . A significant rise in MCT has a high specificity and positive predictive value for an IgE-mediated reaction , which may help guide future testing and management . 1 Note that serum MCT may not increase in some cases of Type 1 reactions to oral agents .
This How to Treat provides an updated overview of the most common drug allergies seen in the community , namely reactions to antibiotics , NSAIDs , local anaesthetics and radiocontrast . It covers the recognition and treatment of these allergic drug reactions , and aims to ensure that GP and non-allergy specialists are confident in managing these in the community .
ANTIBIOTIC ALLERGY
ANTIBIOTIC allergy is reported in 1-4 hospitalised patients , depending on the patient population studied ; for example , age group or underlying diagnosis . 2 , 3 Penicillin allergy is the most reported drug allergy , estimated in 1-9 patients internationally . 3-5 Other commonly encountered antibiotic allergies in hospitalised patients are cephalosporins ( 2.3 %), sulphonamides ( 2.1 %), macrolides ( 1.3 %),
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This information was correct at the time of publication : 15 September 2023