Beta-lactam antibiotics are the most commonly prescribed class of antimicrobials and include penicillins, cephalosporins, carbapenems and monobactams
Due to similarities in their beta-lactam ring structure it has been widely accepted that penicillins, cephalosporins and carbapenems have significant cross-reactivity with other classes of beta-lactams
Historically it has been reported that approximately 10% of patients allergic to penicillins are also allergic to cephalosporins and up to 50% cross-reactivity has been reported between penicillins and carbapenems
Therefore, it has been commonly recommended that patients with a severe allergic reaction to one class of beta-lactam antibiotic should not receive any beta-lactam antibiotic
This historic over-estimation of cross-sensitivity between classes of beta-lactams is inaccurate and based on flawed methodologies
Studies have shown that physicians are more likely to prescribe antimicrobials from other classes when patients have a documented penicillin or cephalosporin allergy
Non beta-lactam alternatives may be: less effective, more toxic, broader spectrum, more expensive and more likely tolead to infection or colonization with resistant organisms
The inaccurate documentation of a penicillin allergy can lead to undesirable patient outcomes
For example, one study showed that patients with a documented penicillin allergy at admission spend more time in hospital and are more likely to be exposed to antibiotics associated with C. difficile and vancomycin resistant Enterococcus
In addition they had increased prevalence rates for infections secondary to C. difficile, vancomycin-resistant Enterococcus and methicillin-resistant Staphylococcus aureus
Practice is changing because allergies have been better defined and the role of the chemical structure on the likelihood of cross-reactivity is now better understood
Recent data shows that the rate of allergic cross-reactivity between penicillins and other beta-lactams is much lower than previous estimates
Determining the nature of the patient’s reaction is an important step in differentiating between an allergic reaction and an adverse drug reaction such as nausea, vomiting, diarrhea and headache
Immunologic reactions to medications are generally classified according to the Coombs and Gell classification of hypersensitivity reactions
The onset and presentation of the reaction can be used to help classify the reaction and determine whether or not a beta-lactam antibiotic may be used
Type-1, immediate hypersensitivity reactions, are immunoglobulin (Ig) E-mediated reactions and are the only true allergic reactions where the potential risk of cross-reactivity between beta-lactams should be considered
Type-1 immediate hypersensitivity reactions usually occur within 1 hour of exposure and typically manifest as anaphylaxis, bronchospasm, angioedema, stridor, wheezing, hypotension, urticaria or a pruritic rash
The incidence of these reactions is very low
Nonurticarial and nonpruritic rashes are almost certainly not IgE-mediated
Management of Penicillin and Beta-Lactam Allergy