Cross reactivity between beta-lactams
- Allergy to all beta-lactams is unlikely to exist.
- Most patients are allergic to the side-chain of the drug rather than the beta-lactam ring; therefore, side chain homology determines cross-reactivity.
- Important cross-reactions include:
- Amoxicillin & 1st-generation cephalosporins (cefalexin/cefazolin)
- Ceftazidime & Aztreonam
- Cross-reactivity between penicillins and cephalosporins is ~2%, and mostly with 1st-generation cephalosporins; cross-reactivity with aztreonam/carbapenems is rare (<1%)
Reasons to delabel patients
- Allows you to use penicillin antibiotics for current infection (and all future infections)
- Avoiding use of beta-lactams is associated with worse outcomes and more side effects
- Patients with a penicillin allergy label are more likely to come to harm through drug toxicity and poor outcomes from using non-beta lactam antibiotics.
- Anaphylaxis/Angioedema: Delabelling these patients is high-risk, and not done as an inpatient.
- People with a history of a Severe Cutaneous Adverse Reaction (SCAR); these are type 4 hypersensitivity reactions,
- Steven-Johnson Syndrome/Toxic Epidermal Necrolysis
- Drug Reaction with Eosinophilia & Systemic Symptoms (DRESS)
- Acute Generalised Exanthematous Pustulosis (AGEP)