EM Quick Hits Video on Penicillin Allergy with Matthew McArther
Penicillin allergy: Who can we safely provide a prescription or challenge dose to?
Allergic reactions to beta lactams are usually caused by the drug’s side chain structures, not the core beta lactam ring. Therefore, you should determine risk of cross reactivity using a cross-reactivity chart when prescribing beta lactams in a patient with known or suspected beta lactam allergy.
Prevalence and harms of erroneous penicillin allergy label
- About 90% of patients who report penicillin allergy can tolerate penicillin with no reaction
- The high rate of erroneous allergy label is due to many reasons
- Misattribution of infectious rashes to penicillin
- The strong tendency for penicillin allergy to fade with time
- Some may report allergy after side effects such as diarrhea
- Some may avoid penicillin due to a family history of penicillin allergy
- The high rate of erroneous allergy label is due to many reasons
- Penicillin allergy labels are harmful to patients
- Labeled patients receive less effective treatments and have higher rates of complications like MRSA and C. Diff, more expensive treatments, longer length of stays, and higher mortality.
Penicillin allergy de-labelling protocols
Patients at very low risk of allergy can be safely prescribed penicillin or offered a challenge dose using validated tools/calculators; very low risk: have never taken penicillin, have tolerated penicillin since the last adverse reaction.
- Point of Care Assessment Tool on dropthelabel.ca
- PEN-FAST Score for estimating risk of penicillin allergy, available on MD Calc: https://www.mdcalc.com/calc/10422/penicillin-allergy-decision-rule-pen-fast. More points = high risk
- F – less than five years since reaction
- A – anaphylaxis or angioedema
- S – severe cutaneous symptoms
- T – treatment required
Who can be safely offered an oral challenge dose or be prescribed penicillin?
- Adults receiving penicillin >10 years ago with an isolated cutaneous symptom without severe symptoms or need for resuscitation
- Children with delayed onset rashes (> 2 hours after a dose or lasting >24 hours) without serious or systemic symptoms
The risk of minor skin reaction using oral protocols is around 5%. The risk of serious reaction/anaphylaxis is extremely low and likely comparable to baseline risk.
Practical bottom line => Most penicillin allergies are erroneous and the label is potentially harmful to patients. You do not need to be an allergist to evaluate or de-label someone at low risk of penicillin allergy. De-labeling is a simple intervention which can improve patient outcomes and antimicrobial stewardship in your community.
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Our EM Quick Hits Video team is: Lara Murphy, Yajur Iyengar and Jonathan Whittall
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