IgE-Mediated Reactions

Actual IgE-mediated penicillin reactions are rare. IgE-mediated symptoms typically cause:

• Acute urticaria

• Nausea

• Vomiting

• Respiratory distress

• Cardiovascular compromise

IgE-mediated penicillin reactions rarely lead to anaphylaxis

Approximately 1/10th of the population will self-report a penicillin allergy; when investigated, only 1/100th of the population will be confirmed to have an IgE-mediated reaction

Further, even if a patient has a history of an IgE-mediated reaction, 80% of these patient’s IgE antibodies to penicillin will fade over 10 years

Symptoms of IgE-mediated hypersensitivity reactions:

• Anaphylaxis

• Angioedema

• Bronchospasm

• Hypotension

• Urticarial rashes

Allergic reactions require prior courses of the same antimicrobial for sensitization to occur and therefore are less common in children

IgE-mediated reactions usually occur within 1 hour of intravenous administration or up to 2 hours after oral administration

In rare instances, IgE-mediated reactions may occur up to 72 hours after exposure

If the reaction is questionable or was very distant (greater than 10 years previously), a drug provocation test or cutaneous allergy testing in hospital following institutional protocols may be used

If the history is convincing, non-beta lactam antimicrobials can be used and referral to an allergist for skin-testing is recommended. If beta-lactam antimicrobials are required in the short term, desensitization may be performed in consultation with Pharmacy and Infectious Disease prior to administration.

Referral to an allergist is recommended if unable to perform drug provocation testing on-site or history is unconvincing.

Contrary to early studies, the cross-reactivity to cephalosporins in patients with a true IgE-mediated penicillin allergy is only about 1 to <3%

Additionally, cross reactivity between cephalosporins is very low

The risk of cross-reactivity between penicillins and cephalosporins is associated with similar side-chains rather than the beta-lactam ring itself, therefore patients with a penicillin allergy may safely use a structurally dissimilar beta-lactam such as:

• IV/PO cefuroxime

• IV cefazolin (not cephalexin)

• Or third-generation cephalosporins