Answer a short set of clinical questions about a reported penicillin allergy and get a structured risk tier with guidance on cephalosporin and carbapenem cross-reactivity.
Use the Penicillin Allergy Risk Stratifier
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Reaction Type
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Timing
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Severity
4
Re-exposure
5
Result
What type of reaction was reported?
Select the best description. If multiple reactions occurred, choose the most severe.
Please select a reaction type before continuing.
When did the reaction begin?
Timing relative to the first dose or re-dose of penicillin.
Please select a timing before continuing.
How severe was the reaction?
Based on what the patient experienced or what is documented in the chart.
Please select a severity before continuing.
Has the patient tolerated penicillin since?
Prior re-exposure without reaction is strong evidence against active sensitization.
Please select a re-exposure history before continuing.
Clinical Guidance
Cross-Reactivity Summary
Drug Class
Estimated Risk
Recommendation
Clinical decision aid only. This tool is not a substitute for clinical judgment, formal allergy evaluation, or institution-specific protocols. High-risk patients or those with ambiguous histories should be referred for penicillin skin testing or a supervised graded challenge. Always confirm allergy documentation and apply shared decision-making.
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Summary
Up to 10% of patients carry a penicillin allergy label, yet studies show fewer than 10–20% of those have a true IgE-mediated reaction on formal testing. Inaccurate labeling drives use of broader-spectrum, less effective, and more toxic alternatives. This tool walks through the clinical history — reaction type, timing, severity, and prior re-exposures — and assigns a risk tier (low, moderate, or high). It then provides practical cross-reactivity guidance for cephalosporins and carbapenems grounded in current AAAAI/ACAAI and IDSA evidence.
How it works
Answer each question about the reported penicillin reaction.
The tool assigns a risk tier (Low / Moderate / High) based on reaction characteristics.
Review the cross-reactivity summary for cephalosporins and carbapenems.
Use the output to inform shared decision-making or referral for allergy testing.
No data leaves your browser — all logic runs client-side.
Use cases
Evaluate a hospitalized patient with a charted penicillin allergy before choosing antibiotics.
Support antimicrobial stewardship delabeling workflows.
Quickly assess whether a cephalosporin can be used safely in a labeled patient.
Educate trainees on beta-lactam cross-reactivity evidence.
Pre-screen candidates for formal penicillin skin testing referral.
Frequently Asked Questions
Cross-reactivity is the risk that a patient allergic to penicillin will also react to another beta-lactam (e.g., a cephalosporin or carbapenem). Shared R1 side chains — not the beta-lactam ring itself — drive most clinically relevant cross-reactions. Overall cephalosporin cross-reactivity in truly penicillin-allergic patients is roughly 1–2%; carbapenems are even lower (~1%).
No. This tool is a clinical decision aid, not a diagnostic test. High-risk patients and those with ambiguous histories should be referred for formal penicillin skin testing (PST) or graded challenge under allergy supervision.
Immediate reactions occur within 1 hour of dosing (urticaria, angioedema, bronchospasm, anaphylaxis) and are most likely IgE-mediated. Delayed reactions occur after more than 1 hour — often days later — and include maculopapular rash, serum-sickness-like reactions, and, rarely, severe cutaneous adverse reactions (Stevens-Johnson syndrome, DRESS).
The highest-risk cephalosporins are those with an identical or similar R1 side chain to amoxicillin/ampicillin: cefadroxil, cefprozil, cefatrizine, and cefaclor. Cephalosporins with dissimilar side chains (ceftriaxone, cefazolin, ceftazidime, etc.) carry very low cross-reactivity risk even in high-risk patients.
Carbapenems (imipenem, meropenem, ertapenem) share the beta-lactam ring but have structurally distinct side chains. Large observational studies place the cross-reactivity rate at approximately 1% or less in penicillin-allergic patients. They are generally considered safe with appropriate monitoring in most risk tiers.
Delabeling is the process of removing an inaccurate or outdated allergy label from a patient's record after evaluation — typically involving history review, skin testing, and/or a supervised oral challenge. Successful delabeling improves antibiotic choices and patient outcomes.
