Predictive factors of amoxicillin immediate hypersensitivity and validation of PEN-FAST clinical decision rule

Ann Allergy Asthma Immunol. 2022 Jan;128(1):27-32. doi: 10.1016/j.anai.2021.07.005. Epub 2021 Jul 13.


Background: The challenge of delabeling amoxicillin allergy is an important issue for patients and clinicians, especially when anaphylaxis is reported. A recent study has proposed a clinical decision rule, PEN-FAST, to identify low-risk penicillin allergies.

Objective: To validate the PEN-FAST clinical decision rule in a population with high risk of suspected immediate amoxicillin allergy and to identify clinical predictive factors of amoxicillin immediate hypersensitivity.

Methods: We retrospectively analyzed medical records of patients with a suspected immediate amoxicillin allergy who carried out an allergologic evaluation by a specialist in the Allergy Unit of Strasbourg University Hospital from 2015 to 2020.

Results: A total of 142 adult patients (88 women [62.0%]; median age, 52 [interquartile range, 40.3-62.0] years) were analyzed. Most of them reported anaphylaxis (68.8%). Internal validation of PEN-FAST score revealed a good discrimination with area under the curve of 0.86 (95% confidence interval, 0.79-0.92). A cutoff of less than 3 points for PEN-FAST was used to classify 29 from 142 patients at low risk of allergy, of whom only 2 (6.9%) received positive results of allergy testing. The negative predictive value for successful delabeling was 0.93 (95% confidence interval, 0.77-0.99). Predictive clinical features for immediate amoxicillin hypersensitivity were time since reaction (P < .001), time elapsed between drug intake and first symptom (P < .001), severity grade reaction (P < .001), and treatment or hospitalization required (P < .001).

Conclusion: PEN-FAST has been validated to identify low-risk penicillin allergies in our European cohort of patients mainly reporting anaphylaxis. This is the first reported external validation of a penicillin allergy clinical decision rule internationally.

Publication types

  • Validation Study

MeSH terms

  • Adult
  • Amoxicillin* / adverse effects
  • Anaphylaxis* / chemically induced
  • Anaphylaxis* / diagnosis
  • Anaphylaxis* / epidemiology
  • Anti-Bacterial Agents / adverse effects
  • Clinical Decision Rules*
  • Drug Hypersensitivity* / diagnosis
  • Drug Hypersensitivity* / epidemiology
  • Female
  • Humans
  • Hypersensitivity, Immediate*
  • Middle Aged
  • Penicillins / adverse effects
  • Retrospective Studies
  • Skin Tests


  • Anti-Bacterial Agents
  • Penicillins
  • Amoxicillin